WELDING of STEEL

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Abstract:

Important Euronorm (EN) standards for welding filler metals are:

1. EN 12072 standard that covers classification of wire electrodes, wires and rods for gas shielded metal arc welding, gas tungsten arc welding, plasma arc welding and submerged arc welding of stainless and heat resisting steels.
2. EN 758 standard, which specifies classification of tubular cored electrodes, for metal arc welding, with or without a gas shield.
3. EN 499 standard, which covers electrodes and deposited metal in the as-welded condition for manual metal arc welding.

Standard EN 12072
The standard EN12072 specifies requirements for classification of wire electrodes, wires and rods for gas shielded metal arc welding, gas tungsten arc welding, plasma arc welding and submerged arc welding of stainless and heat resisting steels. The classification of the wire electrodes, wires and rods is based on their chemical composition.
For stainless steel welding consumables there is no unique relationship between the product form (wire electrode, wire or rod) and the welding process used (gas shielded metal arc welding, gas tungsten arc welding, plasma arc welding or submerged arc welding). For this reason the wire electrodes, wires or rods can be classified on the basis of any of the above product forms and can be used as appropriate, for more than on of the above processes.
A wire electrode, wire or rod is classified in accordance with its chemical composition. The classification is divided into two parts, as follows:

1. The first part gives a symbol indicating the product/process to be identified, as follows:
   G = Gas shielded metal arc welding.
   W = Gas tungsten arc welding.
   P = Plasma arc welding.
   S = Submerged arc welding.
    
2. The second part gives a symbol indicating the chemical composition of the wire electrode, wire or rod. This grade has the symbol 25 20 Mn and is a heat resisting type.

The influence of the shielding gas or flux on the chemical composition of the all-weld metal is considered. Differences between the chemical composition of the all-weld metal and the wire electrode, wire or rod can occur.
Proof and tensile strength of the weld metal made by this grade is expected to conform with the minimum requirements contained in the mechanical properties table. Elongation and impact properties of the weld metal can deviate from the minimum values specified for the corresponding parent metal as a result of variations in the microstructure.

Standard EN 758
This specification specifies the requirements for classification of tubular cored electrodes in the as-welded condition for metal arc welding, with or without a gas shield, of non alloy and fine grain steels with a minimum yield strength of up to 500 N/mm. One tubular cored electrode can be tested and classified with different gases.
The designation contains 6 compulsory and 2 optional parts.
Compulsory Section:
The first part, T, is a symbol denoting that it is a tubular cored electrode used in the metal arc welding process.
The second part, 50, is a symbol denoting the yield strength, tensile strength and elongation of the all-weld metal in the as-welded condition.
The third part is a symbol denoting the temperature at which minimum average impact energy of 47 J of all-weld metal can be achieved, as follows: 
Z = No requirement
A = +20°C
0 = 0°C
2 = -20°C
3 = -30°C
4 = -40°C
5 = -50°C
6 = -60°C
The fourth part, Z, is a symbol indicating the chemical composition of all-weld metal. The symbol Z denotes any agreed composition other than those grades already contained in the specification.
The fifth part is a symbol indicating the type of tubular cored electrode relative to its core composition and slag characteristics, as follows:
R = Rutile, slow freezing slag, single and multiple pass types of weld, requiring a shielding gas.
P = Rutile, fast freezing slag, single and multiple pass types of weld, requiring a shielding gas.
B = Basic, single and multiple pass types of weld, requiring a shielding gas.
M = Metal powder, single and multiple pass types of weld, requiring a shielding gas.
V = Rutile or basic/fluoride, single pass type of weld, not requiring a shielding gas.
W = Basic/fluoride, slow freezing slag, single and multiple pass types of weld, not requiring a shielding gas.
Y = Basic/fluoride, fast freezing slag, single and multiple pass types of weld, not requiring a shielding gas.
Z = Other types.
The sixth part is a symbol indicating the type of shielding gas as follows:
M = mixed gases: EN 439 - M2 but without helium.
C = EN 439 - C1, carbon dioxide
N = This symbol shall be used for tubular cored electrodes without a gas shield.
Optional Section (the next two parts have not been included in the designation for this grade):
The seventh part gives a symbol for the welding position as follows:
1 = all positions;
2 = all positions, except vertical down;
3 = flat butt weld, flat fillet weld, horizontal-vertical fillet weld;
4 = flat butt weld, flat fillet weld;
5 = vertical down and positions according to symbol 3.
The eighth part gives a symbol indicating the hydrogen content of deposited metal as follows:
Symbol Hydrogen content ml/100 g deposited metal
H5 5 maximum
H10 10 maximum
H15 15 maximum

Standard EN 499
This specification specifies the requirements for classification of covered electrodes and deposited metal in the as-welded condition for manual metal arc welding of non alloy and fine grain steels with a minimum yield strength of up to 500 N/mm in the welded condition.
The designation contains 5 compulsory and 3 optional parts.
Compulsory Section: The first part, E, is a symbol denoting that it is a covered electrode used in the manual metal arc welding process.
The second part, 38, is a symbol denoting the yield strength, tensile strength and elongation of the all-weld metal in the as-welded condition.
The third part is a symbol denoting the temperature at which minimum average impact energy of 47 J of all-weld metal can be achieved, as follows: 
Z = No requirement
A = +20°C
0 = 0°C
2 = -20°C
3 = -30°C
4 = -40°C
5 = -50°C
6 = -60°C
The fourth part, 1Ni, is a symbol indicating the chemical composition of all-weld metal.
The fifth part is a symbol indicating the type of electrode covering as follows: 
A = acid covering
C = cellulosic covering
R = rutile covering
RR = rutile thick covering
RC = rutile-cellulosic covering
RA = rutile-acid covering
RB = rutile-basic covering
B = basic covering
Optional Section (the next three parts have not been included in the designation for this grade):
The sixth part gives a symbol for the weld metal recovery and type of current as follows:
Symbol % weld metal recovery Type of current
1 less than or equal to 105 a.c. + d.c.
2 less than or equal to 105 d.c.
3 over 105 up to and inc.125 a.c. + d.c.
4 over 105 up to and inc.125 d.c.
5 over 125 up to and inc.160 a.c. + d.c.
6 over 125 up to and inc.160 d.c.
7 over 160 a.c. + d.c.
8 over 160 d.c.
The seventh part gives a symbol for welding position as follows:
1 = all positions
2 = all positions, except vertical down
3 = flat butt weld, flat fillet weld, horizontal vertical fillet weld
4 = flat butt weld, flat fillet weld
5 = vertical down and positions according to symbol 3
The eighth part gives a symbol indicating the hydrogen content of all-weld metal as follows:
Symbol Hydrogen content ml/100 g all-weld metal
H5 5 maximum
H10 10 maximum
H15 15 maximum

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Abstract:

Stainless steels or, more precisely, corrosion-resisting steels are a family of iron-base alloys having excellent resistance to corrosion. These steels do not rust and strongly resist attack by a great many liquids, gases, and chemicals. Many of the stainless steels have good low-temperature toughness and ductility. Most of them exhibit good strength properties and resistance to scaling at high temperatures. 
Stainless steels can be welded using several different procedures such as shielded metal arc welding, gas tungsten arc welding, and gas metal arc welding.

Stainless steels or, more precisely, corrosion-resisting steels are a family of iron-base alloys having excellent resistance to corrosion. These steels do not rust and strongly resist attack by a great many liquids, gases, and chemicals. Many of the stainless steels have good low-temperature toughness and ductility. Most of them exhibit good strength properties and resistance to scaling at high temperatures. All stainless steels contain iron as the main element and chromium in amounts ranging from about 11% to 30%. Chromium provides the basic corrosion resistance to stainless steels. There are about 15 types of straight chromium stainless steels.
Nickel is added to certain of the stainless steels, which are known as chromium-nickel stainless steel. The addition of nickel reduces the thermal conductivity and decreases the electrical conductivity. The chromium-nickel steels belong to AISI/SAE 300 series of stainless steels. They are nonmagnetic and have austenitic microstructure. These stainless steels contain small amounts of carbon because this element has tendency to make chromium carbides, which are not corrosion resistant. Carbon is undesirable particularly in the 18% chromium, 8% nickel group.
Manganese is added to some of the chromium-nickel alloys. Usually these steels contain slightly less nickel since the chromium-nickel-manganese alloys were developed originally to conserve nickel. In these alloys, a small portion of nickel is replaced by manganese, generally in a two-to-one relationship. The AISI/SAE 200 series of stainless steels are the chromium-nickel-manganese series. These steels have an austenitic microstructure and they are nonmagnetic.
Molybdenum is also included in some stainless steel alloys. Molybdenum is added to improve the creep resistance of the steel at elevated temperatures. It will also increase resistance to pitting and corrosion in many applications.
Stainless steels can be welded using several different procedures such as shielded metal arc welding, gas tungsten arc welding, and gas metal arc welding.
These steels are slightly more difficult to weld than mild carbon steels. The physical properties of stainless steel are different from mild steel and this makes it weld differently. These differences are:

• Lower melting temperature,
• Lower coefficient of thermal conductivity,
• Higher coefficient of thermal expansion,
• Higher electrical resistance.

The properties are not the same for all stainless steels, but they are the same for those having the same microstructure. Regarding this, stainless steels from the same metallurgical class have the similar welding characteristics and are grouped according to the metallurgical structure with respect to welding.
Austenitic Type. Manganese steels are not hardenable by heat treatment and are nonmagnetic in the annealed condition. They may become slightly magnetic when cold worked or welded. This helps to identify this class of stainless steels. All of the austenitic stainless steels are weldable with most of the welding processes, with the exception of Type 303, which contains high sulphur and Type 303Se, which contains selenium to improve machinability.
The austenitic stainless steels have about 45% higher thermal coefficient of expansion, higher electrical resistance, and lower thermal conductivity than mild-carbon steels. High travel speed welding is recommended, which will reduce heat input and carbide precipitation, and minimize distortion.
The melting point of austenitic stainless steels is slightly lower than melting point of mild-carbon steel. Because of lower melting temperature and lower thermal conductivity, welding current is usually lower. The higher thermal expansion dictates that special precautions should be taken with regard to warping and distortion. Tack welds should be twice as often as normal. Any of the distortion reducing techniques such as back-step welding, skip welding, and wandering sequence should be used. On thin materials it is very difficult to completely avoid buckling and distortion.
Ferritic Stainless Steels. The ferritic stainless steels are not hardenable by heat treatment and are magnetic. All of the ferritic types are considered weldable with the majority of the welding processes except for the free machining grade 430F, which contains high sulphur content. The coefficient of thermal expansion is lower than the austenitic types and is about the same as mild steel. Welding processes that tend to increase carbon pickup are not recommended. This would include the oxy-fuel gas process, carbon arc process, and gas metal arc welding with CO2 shielding gas.
The lower chromium types show tendencies toward hardening with a resulting martensitic type structure at grain boundaries of the weld area. This lowers the ductility, toughness, and corrosion resistance at the weld. For heavier sections preheat of 200°C is beneficial. To restore full corrosion resistance and improve ductility after welding, annealing at 760-820°C, followed by a water or air quench, is recommended. Large grain size will still prevail, however, and toughness may be impaired. Toughness can be improved only by cold working the weld.
If heat treating after welding is not possible and service demands impact resistance, an austenitic stainless steel filler metal should be used. Otherwise, the filler metal is selected to match the base metal.
Martensitic Stainless Steels. The martensitic stainless steels are hardenable by heat treatment and are magnetic. The low-carbon type can be welded without special precautions. The types with over 0.15% carbon tend to be air hardenable and, therefore, preheat and postheat of weldments are required. A preheat temperature range of 230-290°C is recommended. Postheating should immediately follow welding and be in the range of 650-760°C, followed by slow cooling.
If preheat and postheat are not possible, an austenitic stainless steel filler metal should be used. Type 416Se is the free-machining composition and should not be welded. Welding processes that tend to increase carbon pickup are not recommended. Increased carbon content increases crack sensitivity in the weld area.

Welding filler metals
The selection of the filler metal alloy for welding the stainless steels is based on the composition of the stainless steel. The various stainless steel filler metal alloys are normally available as covered electrodes and as bare solid wires. Recently flux-cored electrode wires have been developed for welding stainless steels.
Filler metal alloy for welding the various stainless steel base metals are: Cr-Ni-Mn (AISI No. 308); Cr-Ni-Austenitic (AISI No. 309, 310, 316, 317, 347); Cr-Martensitic (AISI No. 410, 430); Cr-Ferritic (AISI No. 410, 430, 309, 502). It is possible to weld several different stainless base metals with the same filler metal alloy.

Welding procedures
For shielded metal arc welding, there are two basic types of electrode coatings. These are the lime type indicated by the suffix 15 and the titanium type designated by the suffix 16. The lime type electrodes are used only with direct current electrode positive (reverse polarity). The titanium-coated electrode with the suffix 16 can be used with alternating current and with direct current electrode positive. Both coatings are of the low-hydrogen type and both are used in all positions. However, the type 16 is smoother, has more welder appeal, and operates better in the flat position. The lime type electrodes are more crack resistant and are slightly better for out-of-position welding. The width of weaving should be limited to two-and-one-half (2,5) times the diameter of the electrode core wire.
Covered electrodes for shielded metal arc welding must be stored at normal room temperatures in dry area. These electrode coatings, of low hydrogen type, are susceptible to moisture pickup. Once the electrode box has been opened, the electrodes should be kept in a dry box until used.
The gas tungsten arc welding process is widely used for thinner sections of stainless steel. The 2% tungsten is recommended and the electrode should be ground to a taper. Argon is normally used for gas shielding; however, argon-helium mixtures are sometimes used for automatic applications.
The gas metal arc welding process is widely used for thicker materials since it is a faster welding process. The spray transfer mode is used for flat position welding and this requires the use of argon for shielding with 2% or 5% oxygen or special mixtures. The oxygen helps producing better wetting action on the edges of the weld. The short-circuiting transfer can also be used on thinner materials. In this case, CO2 shielding or the 25% CO2 plus 75% argon mixture is used. The argon-oxygen mixture can also be used with small-diameter electrode wires. With extra low-carbon electrode wires and CO2shielding the amount of carbon pickup will increase slightly. This should be related to the service life of the weldment. If corrosion resistance is a major factor, the CO2 gas or the CO2-argon mixture should not be used.
For all welding operations, the weld area should be cleaned and free from all foreign material, oil, paint, dirt, etc. The welding arc should be as short as possible when using any of the arc processes.

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Abstract:

The term high-strength steel is often applied to all steels other than mild low-carbon steels. The steels which have yield strength over 560 MPa are sometimes called the ultra-high-strength steels or super alloys.
The groups of steels that fall into this category are:

• Medium-carbon low-alloy hardenable steels.
• Medium-alloy hardenable or tool and die steels.
• High-alloy hardenable steels.
• High-nickel maraging steels.
• Martensitic stainless steels.
• Semi austenitic precipitation-hardenable.

The term high-strength steel is often applied to all steels other than mild low-carbon steels. The steels which have yield strength over 560 MPa are sometimes called the ultra-high-strength steels or super alloys.
The groups of steels that fall into this category are:
Medium-carbon low-alloy hardenable steels

• Medium-alloy hardenable or tool and die steels
• High-alloy hardenable steels
• High-nickel maraging steels
• Martensitic stainless steels
• Semi austenitic precipitation-hardenable stainless steels

Medium-Carbon Low-Alloy Hardenable Steels
The best-known steels in this class are AISI 4130 and AISI 4140 steels. Also in this class are the higher-strength AISI 4340 steel and the AMS 6434steel. These steels obtain their high strength by heat treatment to a full martensitic microstructure, which is tempered to improve ductility and toughness.
Tempering temperatures greatly affect the strength levels of these steels. The carbon is in the medium range and as low as possible but sufficient to give the required strength. Impurities are kept to an absolute minimum because of high-quality melting and refining methods.
These steels are available as sheets, bars, tubing, and light plate. The steels in this group can be mechanically cut or flame cut. However, when they are flame cut they must be preheated to 316°C. Flame-cut parts should be annealed before additional operations in order to reduce the hardness of the flame-cut edges.
These steels are suitable for welding only when they are in the annealed or normalized condition. After welding, they have to be heat treated to obtain the desired strength. The gas tungsten arc, the gas metal arc, the shielded metal arc, and the gas welding process are all used for welding these steels. The composition of the filler metal is designed to produce a weld deposit that responds to a heat treatment in approximately the same manner as the base metal.
In order to avoid brittleness and the possibility of cracks during welding, relatively high preheat and interpass temperatures are used. Preheating is in the order of 316°C. Complex weldments are heat treated immediately after welding.
Aircraft engine parts, aircraft tubular frames, and racing car frames are made from AISI 4130 tubular sections. These types of structures are normally not heat treated after welding.

Medium-Alloy Hardenable Steels
These steels are used largely in the aircraft industry for ultra-high-strength structural applications. They have carbon in the low to medium range and possess good fracture toughness at high-strength levels. In addition, they are air hardened, which reduces the distortion that is encountered with more drastic quenching methods. Some of the steels in this group are known as hot work die steels and another grade has become known as 5Cr-Mo-V aircraft quality steel. These steels are available as forging billets, bars, sheet, strip, and plate.
There is another type of steel in this general class which is a medium-alloy quenched and tempered steel known as high-yield or HY 130/150. This type of steel is used for submarines, aerospace applications, and pressure vessels, and is normally available as plate. This steel has good notch toughness properties at 0°C and below. These types of steels have much lower carbon than the grades mentioned previously.
When flame cutting or welding the aircraft quality steels, preheating is absolutely necessary since the steels are air hardening. A preheating on 316°C is used before flame cutting and then annealed immediately after the flame-cutting operation. This will avoid a brittle layer at the flame-cut edge, which is susceptible to cracking.
These types of steel should only be welded in the annealed condition. The steel should be preheated to 316°C and this temperature must be maintained throughout the welding operation. After welding, the work must be cooled slowly. This can be done by post heating, or by furnace cooling. The weldment is then stress relieved at 704°C and air cooled to obtain a fully tempered microstructure suitable for additional operations. It is usually annealed, after all welding is done, prior to final heat treatment. The filler metal should be of the same com-position as the base metal. The gas tungsten arc and gas metal arc processes are most widely used. However, shielded metal arc welding, plasma arc, and electron beam welding processes can be used.
The medium-alloy quenched and tempered high-yield strength steels are usually welded with the shielded metal arc, gas metal arc, or the submerged arc welding process. The filler metal must provide deposited metal of a strength level equal to the base material. In all cases, a low-hydrogen or no-hydrogen process is required.
For shielded metal arc welding the low-hydrogen electrodes of the E-13018 type are recommended. Electrodes must be properly stored. In the case of the other processes, precautions should be taken to make sure that the gas is dry and that the submerged arc flux is dry. By employing the proper heat input-heat output procedure yield strength and toughness are maintained. Preheating should be at least at 38°C for thinner materials. For heavier materials preheating temperature has to be higher.
The heat input should be such that the adjacent base metal does not become overheated while the heat output is sufficient to maintain the proper microstructure in the heat-affected zone. There may be some softening in the intermixing zone. The properties of welded joints that are properly made will be in the same order as the base metal. Subsequent heat-treating is usually not required or desired.

High-Alloy Hardenable Steels
The steels in this group develop high strength by standard hardening and tempering heat treatments. The steels possess extremely high strength in the range of 1240 MPa yield and have a high degree of toughness. This is obtained with a minimum carbon content usually in the range of 0.20%; however, these steels contain relatively high amounts of nickel and cobalt, and they are sometimes called the 9 Ni-4 Co steels. These steels also contain small amounts of other alloying elements.
They are normally welded in the quenched and tempered condition by the gas tungsten arc welding process. No post-heat treatment is required. The filler metal must match the analysis of the base metal.

High-Nickel Maraging Steels
This type of steel has relatively high nickel, and low carbon content. It obtains its high strength from a special heat treatment called maraging. These steels possess an extraordinary combination of ultra-high-strength and fracture toughness and at the same time are formable, weldable, and easy to heat treat. There are three basic types: the steels with 18% nickel, 20% nickel, and 25% nickel. These steels are available in sheet, forging billets, bars, strip, and plate. Some are available as tubing.
The extra special properties of these steels are obtained by heating the steel to 482°C and allowing it to cool to room temperature. During this heat treatment all of the austenite transforms to martensite. The heating time at the 482°C temperature is extremely important and usually is in the range of three hours. The steels derive their strength while aging at this temperature in the martensitic condition and for this reason are known as maraging steels.
These steels are supplied in the soft or annealed condition. They can be cold worked in this condition and can be flame cut or plasma arc cut. Plasma arc cutting is preferred.
These steels are usually welded by the gas tungsten arc or the gas metal arc welding process. The shielded metal arc and submerged arc process can also be used with special electrode-flux combinations. The filler metal should have the same composition as the base metal. In addition, the filler metal must be of high purity with low carbon. Preheat or postheat is not required; however, the welding must be followed by the maraging heat treatment which produces weld joints of an extremely high strength.

Martensitic Stainless Steels
These steels are of the straight chromium type, such as AISI 420. They contain 12-14% chromium and up to 0.35% carbon. This composition combines stainlessness with high strength. Numerous variations of this basic composition are available, all of which are in the martensitic classification.
This type of steel has been used for compressor and turbine blades of jet engines and for other applications in which moderate corrosion resistance and high strength are required. The strength level of these steels is obtained by a quenching and tempering heat treatment. They can be obtained as sheet, strip, tubing, and plate. The compositions are also used for castings. These steels can be heat treated to strengths as high as 1750 MPa yield strength.
These stainless steels can be flame cut by the powder cutting system normally used for flame cutting stainless steels. They can also be cut with the oxy-arc process. Flame cutting should be done with the steel in the annealed condition. Most grades should be preheated to 316°C because they are air hardenable. They should be annealed after cutting to restore softness and ductility. These materials can also be cold worked in the annealed condition.
The martensitic stainless steels can be welded in the annealed or fully hardened condition, usually without preheat or postheat. The gas tungsten arc welding process is normally used. The filler metal must be of the same analysis as the base metal. Following welding the weldment should be annealed and then heat treated to the desired strength level.

Semiaustenitic Precipitation-Hardenable Stainless Steels
The steels in this group are chrome-nickel steels that are ductile in the annealed condition but can be hardened to high strength by proper heat treatment. In the annealed condition the steels are austenitic and can be readily cold worked. By special heat treatment the austenite is transformed to martensite and later a precipitant is formed in the martensite. The outstanding extra high strength is obtained by a combination of these two hardening processes.
The term semi austenitic type was given these steels to distinguish them from normal stainless steels. They are also called precipitation hardening steelsor PH steels. The heat treatment for these steels is based on heating the annealed material to a temperature between 927°C and 954°C, followed by a tempering or aging treatment in the range of 454-593°C. These steels are available as billets, sheets, tubing, and plates.
These steels are normally not flame cut. Welding is performed using the gas tungsten arc or the gas metal arc welding process. The shielded metal arc welding process is rarely used. The filler metal should have the same composition as the base metal. No preheat or postheat is required if the parts are welded in the annealed condition. After welding, the steel has to be heat-treated to develop optimum strength levels.
However, there is a loss of joint strength due to heating of the heat-affected zone above the aging temperature. In view of this, it is not possible to produce a 100% efficient joint. Extra reinforcing must be utilized to develop full-strength joints. These steels are also brazed using nickel alloy filler metal.
When welding on any of these high-strength steels, weld quality must be of the highest degree. Root fusion must be complete, and there should be no undercut or any type of stress risers. The weld metal should be free of porosity and any weld cracking is absolutely unacceptable. All precautions must be taken in order to produce the highest weld quality.

Abstract:

Repair welding and surfacing are both considered in the field of maintenance welding and are covered together since they are both done by the same welders. Often it is extremely difficult to separate what is considered repair welding from maintenance welding, and surfacing can be included in both situations. The same basic factors apply to both weld repair and surfacing. 
Repaired parts may be more serviceable than the original part, since they can be reinforced and the weaknesses of the original part corrected. It is often more economical to weld repair since the delay in obtaining the replacement part could be excessive and the cost of the new part would normally exceed the cost of repairing the damaged part.

The need for weld repair and surfacing
There are probably more welders employed doing maintenance and repair welding than there are in any other industry grouping. The work done in the primary metal industry is primarily maintenance and repair. This is true also of the utility services category and by combining these with repair services you find that approximately 18% of the welders are engaged in this type of work.
In addition, it has prime importance to welding since the earliest use of welding was for repair work. The most famous incident happened at the outbreak of World War I when German ships were interned in New York harbor. Their crews, hoping to make the ships inoperable, sabotaged the engines and machinery. However, by means of welding, repairs were quickly made and the ships were placed in transatlantic service to deliver material from the U.S. to Europe.
Repair welding and surfacing are both considered in the field of maintenance welding and are covered together since they are both done by the same welders. Often it is extremely difficult to separate what is considered repair welding from maintenance welding, and surfacing can be included in both situations. The same basic factors apply to both weld repair and surfacing.
Parts break and wear out continually. It may be impossible to obtain another part exactly like the one that broke or wore out. This is particularly true of older industrial machinery, construction machinery, agricultural machinery, machine tool parts, and even automobiles. Repaired parts may be more serviceable than the original part, since they can be reinforced and the weaknesses of the original part corrected. It is often more economical to weld repair since the delay in obtaining the replacement part could be excessive and the cost of the new part would normally exceed the cost of repairing the damaged part.
Weld repair is commonly used to improve, update, and rework parts so that they equal or exceed the usefulness of the original part. This is normally attained, with the possible exception of weld-repaired cast iron parts that are subjected to heating and cooling. Weld repairs on cast iron parts subjected to repetitive heating and cooling may or may not provide adequate service life. The problem is that cast iron parts subjected to high-temperature heating and cooling, such as machinery brakes, furnace sections, etc., fail originally from this type of service and due to metallurgical changes the weld may fail again without providing adequate service life. Except for emergency situations, it is not wise to repair cast iron parts of this type.
The metal that the part to be repaired is made of has a great influence on the service life of the repaired parts. Parts made of low-carbon and low-alloy steels can be repaired without adversely affecting the service life of the part. On the other hand, high-carbon steels may be weld repaired but must be properly heat treated if they are to provide adequate service life.
It is absolutely essential that we know the type, specification, or composition of the metal that we are planning to weld. As mentioned above, it may be unwise to weld repair certain metals. But we should not weld on any metal unless we know its composition.
The economics of weld repairing are usually very favorable and this applies to the smallest or the largest weld repair job. Some weld repair jobs may take only a few minutes and others may require weeks for proper preparation and welding. Even so, the money involved in a repair job may be less than the cost of a new part.
A part made of any metal that can be welded can be repair welded or surfaced. In fact, some of the metals that are not normally welded can be given special surfacing coatings by one process or another. All the arc welding processes are used for repair and maintenance work. In addition the brazing processes, the oxy-fuel gas welding processes, soldering, thermit welding, electro slag welding, electron beam welding, and laser beam welding are also used. The thermal spraying processes are all widely used for surfacing applications. In addition, the various thermal cutting processes are used for preparing parts for repair welding.
The selection of the appropriate preparation process and welding process depends on the same factors that are considered in selecting a welding or cutting process for the original manufacturing operation.
In the case of repair welding, there are usually limitations, such as the availability of equipment for a one-time job and the necessity of obtaining equipment quickly for emergency repair work. This limits the selection and it is for this reason that the shielded metal arc welding process, the gas metal arc welding process, the gas tungsten arc welding process, and oxyacetylene welding and torch brazing are most commonly used.
However, for many routine and continuous types of repair work some of the other welding processes may be the most economical. For example, submerged arc welding is widely used for building up the surface of worn parts. The electro slag process has been used to repair and resurface parts for hammer mills, for construction equipment, and for rebuilding rolls for steel mills. Thus there is a difference in the selection of the welding process for the routine, continuing types of repair and surfacing work versus the one-of-a-type or breakdown emergency repair job.

Analyze and develop rework procedure
The success of a repair or surfacing job depends on the thought and preparation prior to doing any actual work on the project. Many factors must be considered in making a thorough analysis. A thorough analysis as outlined may not be required in many situations. This is due to experience gained by welders and others in analyzing jobs, making repairs, and then checking on the service life of the repaired part. As experience is gained many short cuts can be taken, but it is the intent to provide a detailed method of analyzing jobs so that the repair will be as successful as possible.
One of the reasons for such an investigation is to establish the cause of the failure in the case of a broken part or the cause of wear or erosion in the case of a part to be surfaced. The four points outlined are:

• Make a detailed study of the actual parts that failed.
• Learn the background information concerning the specifications and design.
• Make an investigation of the materials used.
• Make a listing of all of the facts so that at the conclusion the reason of failure will be as accurate as possible.

There are certain situations and certain types of equipment for which repair welding may not be done or may be done only with prior approvals.
Certain types of containers and transportation equipment must not be weld repaired or may be welded only with special permission and approval. These include railroad locomotive and car wheels, high-alloy high-strength truck frames, and compressed gas cylinders. Most pieces of power-generating machinery, including turbines, generators, and large engines, are covered by casualty insurance. Weld repair on such machinery can be done only with the prior approval of the welding procedure by the insurance underwriters. In some cases, approval may not be granted. An example of this can be cast iron crankshafts in large stationary diesel engines. Certain weld repairs may be made but it is necessary to develop a written procedure which must be approved in writing by the underwriting company’s representative.
Repairs by welding to boilers and pressure vessels require special attention. Pressure vessels that carry an ASME stamp or are under the jurisdiction of any state or province or government agency must be repaired in accordance with the National regulations issued by responsible authorities.
Repairs by welding are limited to steels having known weldable quality. It provides a maximum carbon content of 0.35% for carbon steels and a carbon content of 0.25% for low-alloy steels.
For welding high-alloy materials and nonferrous materials the work must be done in accordance with the ASME code. Welders making such repairs must be qualified based on the thickness of the material and the type of material being welded. Full-penetration welds are required with welding recommended from both sides. Permissible welded repairs are defined as cracks, corroded surfaces, and seal welding, patches, and the replacement of stays.
A repair is the work necessary to return a boiler or pressure vessel to a safe and satisfactory operating condition. Alterations are also permitted and this is a change in a boiler or pressure vessel that substantially alters the original design and in this case work can be done only by a manufacturer possessing a valid certificate authorization from ASME. All alterations must comply with the section of code to which the original boiler or pressure vessel was constructed.
A written repair procedure is required for doing either repair work or alterations. In the case of an alteration a record must be made and all alteration work must be approved. These records must be filed with the inspection agency or the jurisdictional agency, the National Board of Boiler and Pressure Vessel Inspectors, and all work must be inspected.
Alterations on bridges, large steel frame buildings, and ships may be done only with special authorization. The alteration work must be designed and approved. The welders must be qualified according to the code used and the work must be inspected. Written welding procedures are required.
Once the decision has been made to make a weld repair it is then necessary to establish why the part failed or wore out. This relates to the type of repair job since it also determines whether reinforcing may be required. Reasons for the part to fail or wear out can be among the following:

• Accident
• Misapplication
• Abuse
• Overload.

If the part failed because of an accident or an overload, it may be returned to service with the weld repair made to bring it back to its original strength. The same consideration applies if the part has been abused or misapplied. It may be necessary to reinforce the part so that it will stand temporary overloads, misapplication, or abuse. This decision should be made prior to the weld repair.
In the case of poor workmanship, poor design, or incorrect material the weld repair should eliminate the poor workmanship that was responsible for the failure. In this case, the part would be returned to its original design. If failure is due to poor design, design changes may be required and reinforcement may be added. In a case of wrong material it will be assumed that the material was of a lower strength level which contributed to the failure. In this case reinforcing would be required. If the repair or alteration job is to modify the part, it is necessary that the modification be designed by competent designers who have the knowledge of the design conditions of the original part. This may require reinforcing to make sure the modification or alteration is satisfactory.
Another important factor that must be considered is what results are expected of the repaired or reworked part. Should it be reinforced or should it be redesigned and altered to provide necessary service life? Finally, in the case of surfacing, what better surface could be provided to withstand the service that caused the premature wear or failure? 
Rework Procedure
A written repair procedure is required for all but the most simple jobs. It is absolutely necessary that the type of material being welded is known. This can be found in several ways. If possible, refer to the drawing of the part and the specifications that are shown for the part or parts to be welded.
If this is not possible, particularly in the field or at the maintenance shop, look for clues as to the type of metal involved. Analyze the application of the metal, for clues. For example, an automobile engine block is normally cast iron except for some which might be cast aluminum. Aluminum and iron are easily distinguishable. The spring of an automobile or truck would normally be high-carbon steel. The body structure of a car or truck would be mild steel. The appearance often helps provide clues.
As a final resort it may be necessary to obtain a laboratory analysis of the metal. Filings or a piece of the metal must be sent to a laboratory capable of making such determinations.
The normal method of selecting the welding process will be followed once the material to be welded has been identified. This involves the type of metal, the thickness of the metal, the position of welding, etc. This also leads into the question of filler metal to be used. After this, the normal method of filler metal selection is followed. This involves matching base metal composition, matching the base metal properties, particularly strength, and providing weld metal that will withstand the service involved.
In surfacing, the surface characteristics desired for the finished job depend entirely on the service to which the surface will be exposed. This is based on knowledge and experience and on the fact that the surface has deteriorated to the point that it needs to be reworked or resurfaced. When wear is involved, surfaces can be rebuilt many times without reducing the strength of the part and the service life will be greatly extended.
The repair procedure should be very similar to a procedure developed for welding a critical part. It should include the process and filler metal and the technique to be used in making welds.

Abstract:

There are three most important set of operations for repair welding:

1. Preparation for welding
2. Repair welding
3. Postweld operations

This article introduces actions and procedures for repair welding and surfacing.

There are three most important set of operations for repair welding:

1. Preparation for welding
2. Repair welding
3. Postweld operation

This article introduces actions and procedures for repair welding and surfacing.
Preparation for Welding
A large number of factors should be considered and decisions made before starting to weld.
Safety. The repair welding location or area must be surveyed and all safety considerations satisfied. This can include the posting of the area required by certain regulations, removal of all combustible materials from the area, the draining of fuel tanks of construction equipment, aircraft, boats, trucks, etc. Other precautions include the elimination of toxic materials such as thick coats of lead paint, plastic coverings of metals, etc.
Cleaning. The immediate work area must be clean from all contaminants and this includes removal of dirt, grease, oil, rust, paint, plastic coverings, etc., from the surface of the parts being welded. The method of cleaning depends on the material to be removed and the location of the work piece. For most construction and production equipment, steam cleaning is recommended. When this is not possible solvent cleaning can be used. Blast cleaning with abrasives is also used. For small parts pickling or solvent dip cleaning can be used and, finally, power tool cleaning with brushes, grinding wheels, disc grinding, etc., can be employed. The time spent cleaning a weld repair area will pay off in the long run.
Disassembly. Except for the simplest repair jobs disassembly may be required. This can be related to items mentioned above but also applies to lubrication lines, instrument tubing, wiring, etc. Sometimes it is necessary to disassemble major components such as machinery from machinery frames, etc.
Protection of adjacent machinery and machined surfaces. When repair welding is done on machinery many parts that are not removed should be protected from weld spatter, flame cutting sparks, and other foreign material generated by the repair process. Sheet metal guards or baffles are used to protect adjacent machinery. For machined surfaces, asbestos cloth can be employed. It is wise to secure protective material with wire, clamps, or other temporary bracing. Machined surfaces within five feet of the welding operation should be protected.
Bracing and clamping. On complex repair jobs bracing or clamping may be required. This is because of the heavy weight of parts or the fact that loads may be exerted on the part being weld repaired. If main structural members are to be cut the load must be carried by temporary braces. The braces can be temporarily welded to the structure being repaired.
Lay out repair work. In most repair jobs it is necessary to remove metal so that a full-penetration weld can be made. A layout should be made to show the metal that is to be removed by cutting or gouging to prepare the part for welding. The minimum amount of metal should be removed to obtain a full-penetration weld. The layout should be selected so that welding can be balanced, if possible, and that the bulk of the welding can be made from the more comfortable welding position.
Preheating. The preheating and flame cutting or gouging are parts of the preparation for welding but can be considered part of the welding operation. When flame cutting or gouging is required, preheating should be the same as when welding. It might not be quite as important since stresses are much smaller; however, the thermal shock on the metal can occur in gouging as well as in welding.
Cutting and gouging. The oxygen fuel gas-cutting torch is most often used for this application. Special gouging tips are available and they should be selected based on the particular geometry of the joint preparation. It is possible, by closely watching the cut surface, to find and follow cracks during the flame gouging operation. The edges of the cracks will show since they become slightly hotter. The air carbon arc cutting and gouging process is also widely used for weld repair preparation. Proper power sources and carbons should be selected for the volume of metal to be removed. The technique should be selected to avoid carbon deposit on the prepared metal surface. For some metals the torch or carbon arc might not be appropriate and in these cases mechanical chipping and grinding may be employed.
Grinding and cleaning. The resulting surfaces may not be as smooth as desired and may include burned areas, oxide, etc. Grind the surfaces to clean bright metal prior to starting to weld. For critical work or where there is a suspicion of additional cracks it is wise to check the surface by magnetic particle inspection to make sure that all cracks and defects have been removed.
The above nine steps constitute a listing of steps for weld preparation. Some of these may be eliminated but they should all be considered to properly prepare the joint for welding. 
Repair Welding
Successful repair welding also involves following a logical sequence to make sure that all factors are considered and adequately provided.
Welding procedure. The welding procedure must be available for the use of the welders. It must include the process to be used, the specific filler metals, the preheat required, and any other specific information concerning the welding joint technique.
Welding equipment. Sufficient welding equipment should be available so that there will be no delays. Standby equipment might also be required. This not only includes welding equipment but includes sufficient electrode holders, grinders, wire feeders if required, cables, etc.
Materials. Sufficient materials must also be available for the entire job. This includes the filler metals stored properly for use on the repair. It also includes materials such as insert pieces, reinforcing pieces, etc. Materials also include fuel for maintaining preheat and interpass temperature, shielding gases if used, and fuel for engine powered welding machines.
Alignment markers. Prior to making the weld alignment markers are sometimes used. These can be nothing more than center punch marks made across the joint in various locations.
Welding sequences. The welding sequence should be well described in the welding procedure and can include block welding, back-step sequence welding, wandering sequence welding, and peeling. 
Safety. Finally, safety cannot be overlooked throughout the welding operation. For example, ventilation must be provided when fuel gases are used for preheating, etc.
Weld Quality. The quality of the weld should be continually checked. The final weld should be smooth, there should be no notches, and reinforcing, if used, should fair smoothly into the existing structure. If necessary, grinding should be done to maintain smooth flowing contours.

Postweld Operation
After the weld has been completed, it should be allowed to slow cool. It should not be exposed to winds or drafts, nor should the machinery loads be placed on the repaired part until the temperature has returned to the normal ambient temperature.
Inspection. The finished weld should be inspected for smoothness and quality. This can include nondestructive testing such as magnetic particle, ultrasonic, or X-ray. The repair weld should be of high quality since it is replacing original metal of high quality.
Clean up operation. This includes the removal of strong backs and the smooth grinding of the points where they were attached. It also involves the removal of other bracing and protective covers, etc. In addition, all weld stubs, weld spatter, weld slag, and other residue should be removed from the repair area to make it cleaner than it was originally. Grinding dust is particularly troublesome and every effort should be made to remove it entirely since it is abrasive and can get into working joints, bearings, etc., and create future problems.
Repainting. After the weld and adjacent repair area has been cleaned it should be repainted and other areas should be re-greased in preparation for the re-operation of the machinery.
Reassembly. After cleaning and painting, etc., the pieces of machinery that were taken away are returned. This involves the reassembly of machinery.
Rebuilding and overlaying
Rebuilding and overlaying with weld metal or spray metal are both considered surfacing operations. Surfacing is the deposition of filler metal on a base metal to obtain desired dimensions or properties. Overlay is considered to be a weld or spray metal deposit that has specific properties sometimes unlike the original surface properties.
Rebuilding is used to bring parts back to their original dimensions and properties, such as the rebuilding of worn shafts, repair of parts that were machined undersize, etc. Overlay surfacing is used to return the part to original dimensions but with weld metal having particular properties to reduce wear, erosion, corrosion, etc.
Rebuilding and overlay, or the all-embracing term, surfacing, can be done by many of the welding processes and by the thermal spraying processes. The selection of the process is based on the same factors that are used to select a welding process for fabricating or repairing.
There are some situations in which the thermal spray processes should be selected. The thermal spray processes do not introduce as much heat into the work as the welding processes. Where this is an important requirement, the thermal spray method should be used. It is possible to thermal spray certain materials that cannot be deposited with the welding processes. This applies particularly to the ceramic sprayed coatings or other nonmetallic materials.

Selection of the welding process
The selection of the welding process and the welding procedure and technique is as important as the selection of the deposit alloy. Almost all the arc welding processes and several others can be used for the application of hard facing weld metal.
The shielded metal arc welding process is probably the most commonly used of any of the welding processes for hard facing. It can be used in the field and in the shop and can be applied to small and large parts in any position.
Submerged arc welding is also used for many applications but it is restricted to welding in the flat position. Most often it is used for plant operations and not used in the field. It is often used for repeating applications when the same part is surfaced on a routine basis.
Flux-cored arc welding with and without shielding gas is a popular semiautomatic welding process. It can be used in the field or in the shop and is not restricted to the flat position.
The gas tungsten arc welding process is used for many smaller applications, usually for shop work in which the part can be brought to the shop and manipulated and moved for ease of welding. Gas tungsten arc can be used manually or in an automatic mode with automatic wire feeders, oscillators, etc. It is more expensive than the other processes and for this reason is restricted to the more technical type jobs.
Plasma arc welding is also used much in the same manner as gas tungsten arc. It does have a higher temperature and for this reason can be used in certain cases where gas tungsten arc welding is not applicable. It is again restricted to the smaller types of jobs.
The electroslag welding process is also used for certain special applications. It has been widely used for rebuilding crusher hammers. These can be rebuilt with special fixturing and done quite rapidly with the electroslag process.
Oxyacetylene welding is also used for certain applications. It is widely used for application of specialized cobalt alloys on relatively thin edges.
In general, the process is selected based on normal process selection factors and modified by some of the above comments. Once the process is selected, the next requirement is the selection of the deposited metal to provide the necessary properties.

Abstract:

The deterioration of surfaces is a very real problem in many industries. Wear is the result of impact, erosion, metal-to-metal contact, abrasion, oxidation, and corrosion, or a combination of these. The effects of wear, which are extremely expensive, can be repaired by means of welding. Surfacing with specialized welding filler metals using the normal welding processes is used to replace worn metal with metal that can provide more satisfactory wear than the original. Hardfacing applies a coating for the purpose of reducing wear or loss of material by abrasion, impact, erosion, oxidation, cavitations, etc. 
In order to properly select a hard facing alloy for a specific requirement it is necessary to understand the wear that has occurred and what caused the metal deterioration. The various types of wear can be categrized and defined as follows...

Wear
The deterioration of surfaces is a very real problem in many industries. Wear is the result of impact, erosion, metal-to-metal contact, abrasion, oxidation, and corrosion, or a combination of these. The effects of wear, which are extremely expensive, can be repaired by means of welding. Surfacing with specialized welding filler metals using the normal welding processes is used to replace worn metal with metal that can provide more satisfactory wear than the original. Hardfacing applies a coating for the purpose of reducing wear or loss of material by abrasion, impact, erosion, oxidation, cavitations, etc.
In order to properly select a hard facing alloy for a specific requirement it is necessary to understand the wear that has occurred and what caused the metal deterioration. The various types of wear can be categorized and defined as follows:
Impact wear is the striking of one object against another. It is a battering, pounding type of wear that breaks, splits, or deforms metal surfaces. It is a slamming contact of metal surfaces with other hard surfaces or objects. A good example is the impact encountered by a shovel dipper lip or tamper.
Abrasion is the wearing away of surfaces by rubbing, grinding, or other types of friction. It usually occurs when a hard material is used on a softer material. It is a scraping or grinding wear that rubs away metal surfaces. It is usually caused by the scouring action of sand, gravel, slag, earth, and other gritty material.
Erosion is the wearing away or destruction of metals and other materials by the abrasive action of water, steam or slurries that carry abrasive materials. Pump parts are subject to this type of wear.
Compression is a deformation type of wear caused by heavy static loads or by slowly increasing pressure on metal surfaces. Compression wear causes metal to move and lose its dimensional accuracy. This can be damaging when parts must maintain close dimensional tolerances.
Cavitation wear results from turbulent flow of liquids, which may carry small suspended abrasive particles.
Metal-to-metal wear is a seizing and galling type of wear that rips and tears out portions of metal surfaces. It is often caused by metal parts seizing together because of lack of lubrication. It usually occurs when the metals moving together are of the same hardness. Frictional heat helps create this type of wear.
Corrosion wear is the gradual eating away or deterioration of unprotected metal surfaces by the effects of the atmosphere, acids, gases, alkalies, etc. This type of wear creates pits and perforations and may eventually dissolve metal parts.
Oxidation is a special type of wear indicated by the flaking off or crumbling of metal surfaces, which takes place when unprotected metal is exposed to a combination of heat, air, moisture. Rust is an example of oxidation.
Corrosion (erosion) wear takes place at the same time. This can happen when corrosive liquids flow over unprotected surfaces.
Thermal shock is a problem indicated by cracking or splintering, which is caused by rapid heating and cooling cycles. While not exactly a wear problem it is a deterioration problem and is thus considered here.
Many of the above types of wear occur in combination with one another. It is wise to consider not only one factor, but to look for a combination of factors that create the wear problem in order to best determine the type of hard facing material to apply. This is done by studying the worn part, the job it does, how it works with other parts of the equipment and the environment in which it works. With these factors in mind it is then possible to make a hardfacing alloy selection.

Hardfacing Alloy Selection
Unfortunately, there is no standardized method of classifying and specifying the different surfacing weld rods and electrodes. Many of the hard facing electrodes commercially available are not covered by any of most used specifications. Various filler metal suppliers provide data setting forth classes of service and have categorized their own products within these classes. Many suppliers also provide complete information for using their specific products for various applications and for different industries such as quarrying, steel mills, foundries, etc.
The best system of classification has been established by the American Society for Metals Committee on Hardfacing. In this system, there are five major groups classed according to total alloy content other than iron, with subdivisions based on the major alloying elements. Most of these alloys are available as solid bare filler rod in straightened lengths or in coils or covered electrodes. Some of the materials are available as powder for special applications.
The following is a brief description of the five major groups, what they contain as alloys, and where they are recommended.
Group 1 is the low-alloy steels that, with few exceptions, contain chromium as the principal alloying element. The subgroup 1A has alloy content 2-6% including carbon. These alloys are often used as buildup materials under higher-alloy hard facing materials. The Group 1B is similar except that they have a higher alloy content, ranging from 6-12%. Several alloys in the group have higher carbon content exceeding 2%, and include several alloy cast irons.
The alloys of Group 1 have the greatest impact resistance of all hardfacing alloys except the austenitic manganese steels (Group 2D) and have better wear resistance than low or medium carbon steels. They are the least expensive of the alloy surfacing materials and are extremely popular. They are machinable and have a moderate improvement over the wear properties of the base metal to which they are welded. They have a high compressive strength and fair resistance to erosion and scratch abrasion.
Group 2 contains higher alloyed steels. Group 2A has chromium (Cr) as the chief alloying element with total alloy content of 12-25%. Many of these alloys also contain molybdenum. Those with over 1.75% carbon are medium-alloy cast irons. Group 2B has molybdenum (Mo) as the principal alloying element but many of these also contain appreciable amounts of chromium. The hardfacing alloys of Groups 2A and 2B are more wear resistant, less shock resistant, and more expensive than those in Group 1.
Groups 2A and 2B are quite strong and have relatively high compressive strengths. They are effective for rebuilding severely worn parts and are used for buildup prior to using higher alloy facing materials. They provide high impact resistance and good abrasion resistance at normal temperatures.
Group 2C contains tungsten and modified high-speed tool steels. They are excellent choices at service temperatures up to 590°C (1100°F) and when good resistance coupled with toughness is required. They are not considered as good high abrasion-resistant types but are resistant to hot abrasion up to 590°C (1100°F) and exhibit good metal-to-metal wear at elevated temperatures.
Group 2D are the austenitic manganese steels, which contain either nickel or molybdenum as stabilizers. The alloys in Group 2D are highly shock resistant but have limited wear resistance unless subjected to work hardening. The total alloy content ranges from 12-25%. This group is excellent for metal-to-metal wear and impact when the deposit is work hardened in use. The as-welded deposit hardness is low, from 70 to 230 BHN, but will work harden to 450-550 BHN. The deposit may deform under battering but it will not crack. The deposit should not be heated to above 260°C (500°F), which would cause embrittlement.
Group 3 contains higher-alloyed compositions ranging from 25-50% total alloy. They are all high-chromium alloys and some contain nickel, molybdenum, or both. The carbon can range from slightly under 2% to over 4%. The alloys in this group exhibit better impact, erosion resistance, metal-to-metal wear, and shock resistance than the previous groups. The 3B grouping will withstand elevated temperatures of up to 540°C (1000°F). The 3C group is high in cobalt which improves high-temperature properties. The Group 3 alloys are more expensive than Groups 1 and 2.
The compositions within Group 4 are nonferrous alloys either cobalt base or nickel base with total content of nonferrous metals from 50 to 99%.
The Group 4A alloys are the high-cobalt-based alloys with high percentage of chromium. These alloys are used exclusively for applications subjected to a combination of heat, corrosion, erosion, and oxidation. They are considered the most versatile of the hard facing materials. The alloys with higher carbon are used for applications requiring high hardness and abrasion resistance but when impact is not as important. These alloys are excellent when service temperatures are above 650°C (1200°F). They resist oxidation temperatures of up to 980°C (1800°F).
The Group 4B alloys are the nickel-based alloys which contain relatively high percentages of chromium. This group of alloys is excellent for metal-to-metal resistance, exhibits good scratch abrasion resistance, and corrosion resistance. They will retain hardness to 540°C (1000°F). The alloys with higher carbon content provide higher hardnesses but are more difficult to machine and provide for less toughness. These alloys show good oxidation resistance up to 950°C (1750°F).
The Group 4C alloys are the chrome-nickel cobalt alloys and all are recommended for elevated temperatures. The high-nickel alloy has excellent resistance to hot impact, abrasion, and corrosion and moderate resistance to wear and deformation at elevated temperatures. The medium-nickel alloy has high-temperature wear resistance and impact resistance. It also provides resistance to erosion, corrosion, and oxidation. The low-nickel alloy is used for moderate high temperatures and provides good edge strength, corrosion resistance, and moderate strength.
The Group 5 alloys provide a tungsten carbide weld deposit. This deposit consists of tungsten carbide particles distributed in a metal matrix. The matrix metals include iron, carbon steel, nickel-based alloys, cobalt-based alloys, and copper-based alloys. The tungsten carbide particles are crushed to mesh sizes varying from 8 to 10 down to 100 and have excellent resistance to abrasion and corrosion, and moderate resistance to impact. The matrix material determines the resistance to corrosion and high-temperature resistance. The finish of the deposit depends on the tungsten carbide particle size: the finer the particles the smoother the finish. The deposits are not machinable and are very difficult to grind.

Abstract:

For the successful hard surfacing or overlaying operation a welding procedure should be established. The procedure should be related to the particular part being surfaced and the composition or analysis of the part. It should specify the welding process to be used, the method of application, the prewelding operations such as cleaning, undercutting, etc. 
The welding procedure should also give the preheat and interpass temperature and any special techniques that should be employed, such as the pattern of hardsurfacing, the method of welding whether beading or weaving, the interface between adjacent beads, and finally, any postwelding operations such as peening and the method of cooling. When a properly developed procedure is followed the service life of the job will be predictable.

For the successful hard surfacing or overlaying operation a welding procedure should be established. The procedure should be related to the particular part being surfaced and the composition or analysis of the part. It should specify the welding process to be used, the method of application, the prewelding operations such as cleaning, undercutting, etc.
The welding procedure should also give the preheat and interpass temperature and any special techniques that should be employed, such as the pattern of hardsurfacing, the method of welding whether beading or weaving, the interface between adjacent beads, and finally, any postwelding operations such as peening and the method of cooling. When a properly developed procedure is followed the service life of the job will be predictable.
The selection of the surfacing alloy was discussed. In many cases two separate materials may be required: the buildup alloy, which is used when the part is to be reclaimed or is excessively worn, and the hardfacing alloy. In general, over three layers of hardfacing alloys are not deposited. The hardfacing alloys are considerably more expensive than buildup alloys. The hard-surfacing should be replaced when the hardfacing alloy is worn away.
When deposit exceeds three layers other problems may be encountered such as cracking, etc., which will influence the service life of the deposit. The other factor to be considered is dilution. This is the diluting of the hardfacing alloy with base metal. Excessive dilution will reduce the effectiveness of the hard-facing material. Excessive penetration and poor tie-in of adjacent beads should be avoided.
In common with all welding operations, fabrication, repair, or surfacing, the base metal to be welded must be clean. Shot blasting, grinding, machining, and brushing are all methods for cleaning the base metal prior to welding. A major consideration is the location of finished surface with respect to the worn surface. In many cases, the first layer of surfacing may have sufficient dilution of base metal so that it is unsuitable for the desired service.
In this case, the worn surface should be further removed so that there is sufficient room for two layers of surfacing metal. This will provide a better service life. There are other situations in which the part is to be re-machined after surfacing and it is not recommended that the machining surface be at the interface between weld surfacing metal and the base metal. Here again, pre-machining may be required. This is particularly important when the base metal is of hardenable material.
Preheating, interpass temperature, and cooling of the part being surfaced are as important in surfacing as they are in repair welding or in original fabrication. The factors that apply to the welding of the base metal in normal fabrication should be followed when overlaying with surfacing weld metal. Preheating is used to minimize distortion, to avoid thermal shock, and to prevent surfacing cracking. The temperature of preheat depends on at least two factors, the carbon and the alloy content of the base metal and the mass of the part being surfaced.
A soak type preheat should be used and sufficient time must be allowed for the preheat temperature to stabilize throughout the part. If it is extremely complex in shape, preheat should be increased. If the ambient temperature is low, preheat should also be increased. Any part that is preheated should be maintained at that temperature throughout the entire welding operation and should then be allowed to slow cool.
The base metal composition must be known in order to provide proper preheat temperatures. Certain materials such as austenitic manganese steel should be treated in accordance with the requirements of the steel. In this case preheat should not exceed 260°C (500 °F). Cast iron should be given sufficient preheat. Cast iron is crack sensitive and normally it is not hardsurfaced because it is relatively inexpensive compared to the cost of surfacing metal and it may be more economical to replace the part than to surface it.
The thickness of the surfacing deposit is extremely important. If the deposit is too heavy, problems can be encountered. Hardfacing alloys should be restricted to two layers. The first will include dilution from the base metal, but the second layer should provide the properties expected. Some types of alloys can be used in three layers.
Surfacing for corrosion resistance and others are recommended for use of one layer only. When edges are being built up with surfacing material make sure that sufficient material is removed so that the edge has at least two layers of surfacing metal prior to re-machining or grinding. Consult the manufacturer’s data for the particular product involved.
A weaving technique is recommended instead of stringer bead welding. In addition, the pass thickness or layer thickness should not exceed 5 mm. The adjacent beads must fair into the previous bead to provide as smooth a surface as possible.
There is considerable controversy concerning the exact pattern of welds that should be made when applying the surfacing deposits. In general, the direction of welding should not be transverse to the load on the part. This can create stress concentrations and may affect service life of the part. Diagonally-shaped welds have an advantage in this regard. In certain types of metal, peening is recommended but this is based on the metal. The manufacturer’s instructions should be followed.
Hardfacing by welding is an excellent method of reclaiming parts and will save considerable time and money. It will often reduce downtime of equipment and may keep equipment going without as much downtime. It is considerably cheaper than replacing original parts and should be used whenever possible. It is now becoming popular for original equipment manufacturers to actually hardface wear parts on new equipment to provide better service life of the equipment.
The corrosion of metals is one of the less known but more expensive of the factors that cause premature failures of many things. These range from automobile bodies to chemical plant equipment to ship hulls. The cost of corrosion is difficult to measure but should include the loss of efficiency of operating equipment such as pumps, mixers, valves, etc., as well as total failures. Fortunately, corrosion can be prevented or at least substantially reduced so that metal parts will have a longer life cycle.
One of the best ways to reduce corrosion is to protect the metal with an overlay or surface of a material less susceptible to corrosion in a specific environment. Coated metals such as galvanized steel and clad metals with nonferrous facings have long been used to reduce the effect of corrosion. In more and more applications, surfaces that are sprayed or welded are contributing to longer service life of parts exposed to corrosive atmospheres.
It was mentioned previously that the deterioration of metal surfaces is caused by the combination of factors, such as corrosion and oxidation, corrosion and erosion, or cavitation.
In repairing corroded or deteriorated surfaces it is necessary to analyze the reason for the deterioration. These factors should be considered in designing new surfaces for specific types of service. That is, consideration should be made in selecting a material for overlays to prevent corrosion.
There is considerable confusion in this field concerning the proper terms to use for the weld surface that is applied. The general term surfacing is sometimes used but more often the term cladding is used. The terms weld buildup and buttering have no official status; however, the term corrosion-resistant weld-overlay cladding does provide an understanding of what is being covered in this section.
Cladding of this type is applied for many reasons:

1. to produce a corrosion-resistant surface as on the inside of a nuclear pressurized vessel,
2. to produce a corrosion-resistant material to replace a higher-priced or unavailable high-alloy material,
3. to produce a metallurgical structural composition that is more weldable,
4. to deposit weld metal which would later be used as a filler metal such as in a tube-to-tube sheet weld, or
5. to produce a wear- or erosion-resistant surface.

Various methods or techniques can be used to provide these surfaces, such as explosive clad metal, roll bond clad, and loose cladding liners, plug and seam welded to the inside of a vessel or tank. Many of the welding processes can be used for applying liners. When attaching liner plates or sheets to carbon mild steel the problems of welding dissimilar metals must be considered. This involves the metallurgical requirements of the clad material and the compatibility of the two materials.
When the solid solubility, that is, ability of one element to be dissolved in another, is exceeded, cracking may occur. In addition, the effects of elements such as sulfur and phosphorous from dilution can be a source of trouble. The welding technique and procedure involving the selection of filler metals, coatings, fluxes, etc., must be considered as with any dissimilar welding operations. These same factors apply whether the material is being applied as a weld surfacing or as separate sheets or plates welded to the carbon steel structure.
There are a number of alloys that are used for overlays or clads for corrosion and oxidation resistance. These are usually standardized compositions commonly used by themselves for the same requirements. These are summarized as follows.
The copper-based alloys are used for certain corrosion requirements. The copper silicon alloys and the copper tin alloys are used for certain corrosion-resistance requirements.
The austenitic stainless steels, which include the standard alloy types 308, 309, 310, 316, and 347, are all used for corrosion-resistant surfaces. These alloys exhibit moderate resistance to high-stress abrasion and have excellent oxidation-resistance and impact properties.
The nickel-base alloys are also used for this purpose. This includes 100% nickel, the Monel (67 Ni-30 Cu) and Inconel (72 Ni-7 Fe-16 Cr). These alloys are frequently used as overlays on carbon and low-alloy steels for cladding of tanks and vessels.
The high-cobalt chromium alloys are used for specific overlays when corrosion is a major problem. These are used quite often in refineries where high pressures, high temperatures, and corrosive materials are pumped and stored. These alloys can be applied in several ways; as a powder applied by the plasma process, as a cold wire, or by covered electrodes with the shielded metal arc welding process. The selection of the overlay is based entirely on the requirements of the materials to which the product is exposed. The selection must be based on normal metallurgical factors.
A unique but rather typical application of weld overlay is used in the repairing of digesters used in pulp and paper mills. Digesters are tanks or pressure vessels ranging in height from 25-50 ft and in diameter from 8-12 ft. They are used for the first chemical processing step of converting wood chips into pulp for paper manufacturing, primarily in the sulphate or kraft paper process.
The wood chips are placed in the digester and are cooked in a highly corrosive alkaline solution. The mixture of wood chips and alkaline liquor is under pressure and operates at a relatively high temperature. The digester is made of carbon steel of from 1 to 2 inches thick. The internal surfaces of digesters corrode at a high rate at the surface of the liquor due to the corrosive action of the alkaline solution. The steel walls of the vessel will gradually deteriorate until they become so thin that pressures and temperatures must be reduced for safety. Unless the metal is replaced by welding the digester will eventually become unsafe and will have to be abandoned.
Welding has been employed to repair the pitted or corroded areas and to rebuild wall thickness to original dimension. Originally, carbon steel weld metal was used. It was found, however, that stainless steel electrodes provide a surface that is less subject to the corrosive action. Tests revealed that stainless overlay outlasts the original carbon steel many times.
Recently the gas metal arc welding (GMAW) process has been used for this overlaying operation. Automatic methods have been used to make the overlay welds more rapidly than with manual application. The automatic application will deposit weld metal in horizontal beads on the vertical inside circumference of the tank. The automatic welding heads are mounted on a boom that rotates about the centerline of the tank and deposits metal as it revolves inside the tank. It is possible to utilize two or even three automatic heads that automatically travel around the inside circumference of the tank. This work is done starting at the lower portion to be welded and moves upwards as it revolves. The most popular procedure uses either 316 or 310 stainless alloy in the 0.035-in. diameter electrode wire with argon for shielding.
In normal applications the inside diameter of the digester is prepared for welding by grit blasting the entire surface to be welded. This may be followed by an acid wash and water rinse. The welding operation, once it is begun, is usually continuous to eliminate any voids in the surface. Each pass must fair smoothly into the previous one and the depth of the surface should be from 1/8 to 3/16 of an inch thick.
This technique is used occasionally for new digesters to reduce the rate of corrosion and the length of time between maintenance repair work. Penetration must be closely controlled so that dilution will not appreciably lower the alloy content of the deposit.
Other procedures for accomplishing an overlay on the inside diameter of smaller tanks are done by rotating the tank and doing the welding in the flat position. In this case, the welding is done by the submerged arc process using one or more electrode wires. There are some situations in which the strip overlay method is used. The submerged arc welding process increases the speed of making the overlay. In some cases the gas tungsten arc welding (GTAW) or plasma hot wire process is used. The process should be selected which is most appropriate for the position and the job to be done.
Normally single layers are used; however, for certain applications such as pump linings and wear areas a second layer of surfacing is applied. The second layer can be made with an electrode of lower alloy content since the dilution factor is drastically reduced.

Abstract:

Selection of a welding process is determined primarily by the characteristics of the joint, the materials involved, their shape and thickness, and joint design. Additionally, production requirements, such as rate and quality, must also be considered. 
Only after the process has been determined can the proper power supply and accessory equipment be chosen. The process is the primary factor in their selection.

Selection of a welding process is determined primarily by the characteristics of the joint, the materials involved, their shape and thickness, and joint design. Additionally, production requirements, such as rate and quality, must also be considered. Only after the process has been determined can the proper power supply and accessory equipment be chosen. The process is the primary factor in their selection.
It is our purpose in this article to provide a guide to the selection of power supplies for some of the welding processes, which have come into maturity during the past decade. Once thought of primarily as special processes or processes designed primarily for mass production operations, they are now found in virtually every area of metal fabrication. The increase in the fabrication of once difficult-to-weld metals and the economic and qualitative advantages of the more advanced welding processes are today recognized by even the smallest metal fabricating shops.
Power and control requirements for these processes are somewhat more sophisticated than for conventional shielded metal arc or stick electrode welding. But since the average metallurgist or welding engineer isn’t an electrical expert, the selection of proper power supply and the reasons for it can be confusing. The purpose of this article is to eliminate some of this mystery through the examination of the power requirements of production welding processes.
The basic types of power supplies are:

• constant current and
• constant voltage.

Constant Current Power Supply
The conventional stick electrode welder is sometimes called a ’constant current machine’. It is also called a ’dropper’ because its voltage drops as welding current increases, thus its volt- ampere output curve ’droops’.
With the machine turned on but with no arc, and hence no current flowing, it has a relatively high open circuit voltage of 70-80 volts. Generally speaking welding is done at the steeper portions of the curve and this is ideal for manual stick electrode welding.
Arc voltage depends upon the physical length of the arc between the electrode and the work and this can never be held completely constant in manual welding. But, since rate of burn off of filler metal is determined by the amount of current, burn off stays substantially constant if current doesn’t vary.
There are many variations of this type of machine based upon power input (single or three phase), output (ac, dc, or ac/dc), and the type of output control (mechanical or electrical).

Constant Voltage Power Supply
The other basic type of arc welding power supply produces a constant voltage. Thus at any voltage setting current may vary from zero to an extremely high short circuit current. Such a machine is designed specifically for gas shielded metal arc welding and is not generally suitable for stick electrode welding.
Actually, no welding machine can produce a truly constant voltage. In practice, voltage drops at least 1 volt for each 100 amp output. Nevertheless, short circuit currents may be as high as several thousand amperes.
Normally, constant voltage machines have lower open circuit voltages than the constant current machines, about 50 volts maximum as compared to 80 volts. As a means of obtaining the desired arc voltage, the operator sets open circuit voltage, rather than current, at the machine. Settings may range from 10 to 48 volts.
Welding current can reach several thousand amperes at short circuit. Current adjusts itself to burn off filler metal at a rate sufficient to maintain the arc length required by the present voltage and is thus determined by the rate of electrode feed.

Duty Cycle
All welding machines are rated according to their duty cycle. Understanding this term is of utmost importance and it is often misunderstood. Duty cycle is based upon a ten minute time period. At rated voltage, a power supply with a 100% duty cycle rating can operate continuously at or below its rated current.
A 60% duty cycle does not mean that it can operate 60% of an indeterminate time at rated current and voltage. It means that the welder should operate only 6 out of every 10 minutes at that current and voltage. It should be allowed to idle 4 out of every 10 minutes for cooling. Machines rated for less than 100% duty cycle can be used continuously by decreasing their current rating.

Tungsten Arc Welding
Tungsten arc welding, using inert shielding gases, is hardly a new process. Nevertheless, it should be covered in any survey of advanced welding processes because of its particular applicability to difficult welding problems. This includes joining hard-to-weld and exotic materials such as the stainless steels, aluminum, magnesium, copper, beryllium copper, Hastelloy, Inconel, Invar and Kovar, especially in very thin cross sections.
Essentially, TIG welding calls for the same type of power source as shielded metal arc, or stick electrode welding, that is one with a drooping volt-ampere output curve. However, the process does present some problems which make a machine especially designed for the process much more suitable.
It should be noted that a conventional AC power source not specifically designed for TIG welding must be derated for AC TIG service. This is because partial rectification occurring at the arc introduces a DC component, which causes overheating of the main transformer. Other problems associated with TIG welding which are more acute than in conventional metallic arc work include arc starting, arc stabilization, and, of course, as the work becomes more delicate, control of all welding variables.

Gas Metal Arc Processes
Gas metal arc welding, in which a consumable wire electrode is fed continuously to a gas shielded arc zone, has replaced non-consumable tungsten inert gas welding and conventional shielded metal arc (stick electrode) welding in many applications. The main reason is its speed. Where it can be used, it is usually several times faster than other processes.
Other advantages include: cleaner welds, because the shielding gas greatly reduces and often prevents oxide formation; electrode savings through the virtual elimination of stub losses; excellent weld metallurgical and physical characteristics: and simplicity of operation which increases weld quality and reproducibility and generally reduces the human variable.

Arc Spot Welding
Arc spot welding has become very popular in recent decades. Its chief advantage is the ability to spot weld from one side of the work. In addition, it is a fast method of producing multiple spot welds with a high degree of reproducibility.

TIG Spot Welding
Arc spot welding may be performed either by tungsten inert gas or gas shielded metal arc processes. For tungsten spot welding the same type of power supply used for regular TIG welding may be employed. However, it requires a special spot welding gun and controls.
TIG spot welding involves the fusion of the parent metal only. Filler wire is not used. Generally TIG spot welding is performed on cold rolled and stainless steels.
MIG Spot Welding
Gas shielded metal arc spot welding is characterized by high amperages. Machines designed for this purpose normally have higher volts. Welding currents with smaller diameter wires up to about 1/16 in. may reach 500 amp. Wires 1/16 in. diameter and larger call for welding currents up to 750 amp. As in TIG spot welding, special controls are required. These are normally incorporated in a special wire drive and control unit.
Plasma Arc Welding
An extension of the commercially accepted plasma cutting technique and similar in some respects to the tungsten inert gas process, it has fewer limitations than such methods as electron beam, laser and ultrasonic welding and at far less initial cost.
Like tungsten inert gas welding, plasma welding is normally a fusion process although cold filler wire may also be employed, depending on the job. The electrode is tungsten coated and water cooled because of the high temperatures involved. The process differs from TIG welding in that, in addition to a shielding gas, a plasma forming gas is also involved. The plasma ’flame’, sometimes in combination with an electric arc can produce extremely high temperatures. The flow of the plasma can be focused by the design of the torch and as a result can be highly concentrated to produce deep, narrow penetration.

Abstract:

Most clad metals are composites of a cladding metal such as stainless steel, nickel and nickel alloys, and copper and copper alloys welded to a backing material of either carbon or alloy steel. The two metals are welded together at a mill in a roll under heat and pressure. The clad composite plates are usually specified in a thickness of the cladding which ranges from 5% to 20% of the total composite thickness. The advantage of composite material is to provide at relatively low cost the benefits of an expensive material which can provide corrosion resistance, abrasion resistance, and other benefits with the strength of the backing metal.

Most clad metals are composites of a cladding metal such as stainless steel, nickel and nickel alloys, and copper and copper alloys welded to a backing material of either carbon or alloy steel. The two metals are welded together at a mill in a roll under heat and pressure. The clad composite plates are usually specified in a thickness of the cladding which ranges from 5% to 20% of the total composite thickness. The advantage of composite material is to provide at relatively low cost the benefits of an expensive material which can provide corrosion resistance, abrasion resistance, and other benefits with the strength of the backing metal.
Clad metals were developed in the early 1930s and one of the first to be used was nickel bonded to carbon steel. This composite was used in the construction of tank cars. Other products made of clad steels are heat exchangers, tanks, processing vessels, materials-handling equipment, storage equipment, etc.
Clad or composites can be made by several different welding manufacturing methods. The most widely used process is roll welding which employs heat and roll pressure to weld the clad to the backing steel. Explosive welding is also used and weld surfacing or overlay is another method of producing a composite material.
Clad steels can have as the cladding material chromium steel in the 12-15% range, stainless steels primarily of the 18/8 and 25/12 analysis, nickel base alloys such as Monel and Inconel, copper-nickel, and copper. The backing material is usually high-quality steel of the ASTM-A285, A212, or similar grade. The tensile strength of clad material depends on the tensile strength of its components and their ratio to its thickness. The clad thickness is uniform throughout the cross section, and the weld between the two metals is continuous throughout.
A slightly different procedure is used for oxygen cutting of clad steel. All of the clad metals mentioned above can be oxygen flame cut with the exception of the copper-clad composite material. The normal limit of clad plate cutting is when the clad material does not exceed 30% of the total thickness. However, higher percentage of cladding may be cut in thicknesses of 12 mm and over. The oxygen pressure is lower when cutting clad steel; however, larger cutting tips are used.
The quality of the cut is very similar to the quality of the cut of carbon steel. When flame cutting clad material the cladding material must be on the underside so that the flame will first cut the carbon steel. The addition of iron powder to the flame will assist the cutting operation.
Schedules of flame cutting are provided by clad steel producers as well as flame-cutting equipment producers. For oxygen flame cutting copper and copper-nickel clad steels the copper clad surface must be removed and the backing steel cut in the same fashion as bare carbon steel.
Copper and brass clad plate can be cut using iron powder cutting. Clad steels can be fabricated by bending and rolling, shearing, punching, and machining in the same manner as the equivalent carbon steels. Clad materials can be preheated and given stress relief heat treatment in the same manner as carbon steels. However, stress relieving temperatures should be verified by consulting with the manufacturer of the clad material.
Clad materials can be successfully welded by adopting special joint details and following specific welding procedures. Special joint details and welding procedures are established in order to maintain uniform characteristic of the clad material. Inasmuch as the clad material is utilized to provide special properties it is important that the weld joint retain these same properties. It is also important that the structural strength of the joint be obtained with the quality welds of the backing metal.
The normal procedure for making a butt joint in clad plate is to weld the backing or steel side first with a welding procedure suitable for the carbon steel base material being welded. Then the clad side is welded with the suitable procedure for the material being joined. This sequence is preferable in order to avoid the possibility of producing hard brittle deposits, which might occur if carbon steel weld metal is deposited on the clad material.
Different joint preparations can be used to avoid the possible pickup of carbon steel in the clad alloy weld. Any weld joint made on clad material should be a full-penetration joint. When designing the joint details it is wise to make the root of the weld the clad side of the composite plate. This may not always be possible; however, it is more economical since most of the weld metal can be of the less expensive carbon steel rather than the expensive alloy clad metal.
The selection of the welding process or processes to be used would be based on that normally used for welding the material in question in the thickness and position required. Shielded metal arc welding is probably used more often; however, submerged arc welding is used for fabricating large thick vessels and the gas metal arc welding process is used for medium thicknesses; the flux-cored arc welding process is used for the steel side, and gas tungsten arc welding is sometimes used for the thinner materials, particularly the clad side.
The selection of process should be based on all factors normally considered. It is important to select a process that will avoid penetrating from one material into the other. The welding procedure should be designed so that the clad side is joined using the appropriate process and filler metal to be used with the clad metal and the backing side should be welded with the appropriate process and filler metal recommended for the backing metal. For code work the welding procedure must be qualified in accordance with the specification requirements.
The normal procedure, assuming that the material is properly prepared and fitted is as follows. The backing side or steel side would be welded first. The depth of penetration of the root pass must be closely controlled by selecting the proper procedure and filler metal. It is desirable to produce a root pass which will penetrate through the root of the backing metal weld joint into the root face area yet not come in contact with the clad metal.
A low-hydrogen deposit is recommended. If penetration is excessive and the root bead melts into the clad material because of poor fitup or any other reason the deposit will be brittle. If this occurs the weld will have to be removed and remade. However, if the penetration of the backing steel root bead is insufficient the amount of back gouging will be excessive and larger amounts of the clad material weld metal will be required. The steel side of the joint should be welded at least half way prior to making any of the weld on the clad side. If warpage is not a factor, the steel side weld can be completed before welding is started on the clad side.
The clad side of the joint is prepared by gouging to sound metal or into the root pass made from the backing steel side. This can be done by air carbon arc gouging or by chipping. The gouging should be sufficient to penetrate into the root pass so that a full penetration of the joint will result. This will determine the depth of the gouging operation. It is also a measure of the depth of penetration of the root pass. Grinding is not recommended since it tends to wander from the root of the joint and may also cover up an unfused root by smearing the metal. If the depth of gouging is excessive, weld passes made with the steel electrode may be required to avoid using an excessive amount of clad metal electrode.
On thin materials the gas tungsten arc welding process may be used, on thicker materials the shielded metal arc welding process or the gas metal arc process may be used. The filler metal must be selected to be compatible with the clad metal analysis.
There is always the likelihood of diluting the clad metal deposit by too much penetration into the steel backing metal. Special technique should be used to minimize penetration into the steel backing material. This is done by directing the arc on the molten puddle instead of on the base metal.
When welding copper or copper nickel clad steels a high nickel electrode is recommended for the first pass (ECuNi or ENi-1). The remaining passes of the joint in the clad metal should be welded so that the copper or copper nickel electrode matches the composition of the clad metal.
When the clad metal is stainless steel the initial pass which might fuse into the carbon steel backing should be of a richer analysis of alloying elements than necessary to match the stainless cladding. This same principle is used when the clad material is Inconel or Monel. The remaining portion of the clad side weld should be made with the electrode compatible with or having the same analysis as the clad metal. The procedure should be designed so that the final weld layer will have the same composition as the clad metal.
On heavier thicknesses where the weld of the backing steel is made from both sides it is important to avoid allowing the steel weld metal to come in contact or to fuse with the clad metal. This will cause a contamination of the deposit which may result in a brittle weld.
When welding thinner gauge clad plate and inside clad pipe it may be more economical to make the complete weld using the alloy weld metal compatible with the clad metal instead of using two types of filler metal. The alloy filler metal must be compatible with the steel backing metal. The expense of the welding filler metal may be higher, but the total weld joint may be less expensive because of the more straightforward procedure. Joint preparation may also be less extensive using this procedure.
For medium thickness, the joint preparation is a single vee or bevel without a large root face. The root face is obtained by grinding the feather edge to provide a small root face. If possible the face of the weld will be the steel or backing side of the joint. The backing side or steel side is welded first using the small diameter electrode for the root pass to insure complete penetration.
If the composite is a pipe or if it must be welded from one side, the buttering technique should be used. In this case the filler metal must provide an analysis equal to the clad metal and be compatible with the backing steel. Weld passes are made on the edge of the composite to butter the clad and backing metal. The buttering pass must be smoothed to the design dimensions prior to fitup. The same electrode can be used to make the joint.
When welding heavy, thick composite plate the U groove weld joint design is recommended instead of the vee groove in order to minimize the amount of weld metal. The same principles mentioned previously are used.
When the submerged arc welding process is used for the steel side of the clad plate caution must be exercised to avoid penetrating into the clad metal. This same caution applies to automatic flux-cored arc welding or gas metal arc welding. A larger root face is required and fitup must be very accurate in order to control root bead penetration.
The submerged arc process can also be used on the clad side when welding stainless alloys. However, caution must be exercised to minimize dilution of a high-alloy material with the carbon steel backing metal. The proper filler metal and flux must be utilized. To minimize admixture of the final pass it is recommended that the clad side be welded with at least two passes so that dilution would be minimized in the final pass.
Special quality control precautions must be established when welding clad metals so that undercut, incomplete penetration, lack of fusion, etc., are not allowed. In addition, special inspection techniques must be incorporated to detect cracks or other defects in the weld joints. This is particularly important with respect to the clad side which may be exposed to a corrosive environment.

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Abstract:

Besides basics on special steels, this article describes techniques applicable for welding special steels, such as
  abrasion-resisting steel
  free machining steels
  manganese steels and
  silicon steels.

Abrasion-Resisting Steel
Abrasion-resisting steel (AR) is carbon steel usually with a high-carbon analysis used as liners in material-moving systems and for construction equipment where severe abrasion and sharp hard materials are encountered. Abrasion-resisting steels are often used to line dump truck bodies for quarry service, for lining conveyors, chutes, bins, etc.
Normally the abrasion-resisting steel is not used for structural strength purposes, but only to provide lining materials for wear resistance. Various steel companies make different proprietary alloys that all have similar properties and, in general, similar compositions. Most AR steels are high-carbon steel in the 0.80-0.90% carbon range; however some are low carbon with multiple alloying elements.
These steels are strong and have hardness up to 40 HRc or 375 BHN. Abrasion-resisting bars or plates are welded to the structures and as they wear they are removed by oxygen cutting or air carbon arc and new plates installed by welding.
Low-hydrogen welding processes are required for welding abrasion-resisting steels. Local preheat of 400°F (204°C) is advisable to avoid underbead cracking of the base metal or cracking of the weld. In some cases this can be avoided by using a preheat weld bead on the carbon steel structure and filling in between the bead and the abrasion-resisting steel with a second bead in the groove provided. The first bead tends to locally preheat the abrasion-resisting steel to avoid cracking and the second bead is made having a full throat. Intermittent welds are usually made since continuous or full-length welds are usually not required. Efforts should be made to avoid deep weld penetration into the abrasion-resisting steel so as not to pick up too much carbon in the weld metal deposit. If too much carbon is picked up the weld bead will have a tendency to crack.
When using the shielded metal arc welding process the E-XX15, E-XX16, or E-XXX8 type electrodes are used. When using gas metal arc welding the low penetrating type shielding gases such as the 15% argon-25% CO2 mixture should be used. The flux-cored arc welding process is used and the self-shielding version is preferred since it does not have the deep penetrating quality as the CO2 shielded version.
During cold weather applications, it is recommended that the abrasion-resistant steel be brought up to 100°F (38°C) temperature prior to welding.

Free Machining Steels
The term free machining can apply to many metals but it is normally associated with steel and brass. Free machining is the property that makes machining easy because small cutting chips are formed. This characteristic is given to steel by sulfur and in some cases by lead. It is given to brass by lead.
Sulfur and lead are not considered alloying elements. In general, they are considered impurities in the steel. The specifications for steel show a maximum amount of sulfur as 0.040% with the actual sulfur content running lower, in the neighborhood of 0.030%. Lead is usually not mentioned in steel specifications since it is not expected and is considered a "tramp" element. Lead is sometimes purposely added to steel to give it free-machining properties.
Free-machining steels are usually specified for parts that require a considerable amount of machine tool work. The addition of the sulfur makes the steel easier to turn, drill, mill, etc., even though the hardness is the same as a steel of the same composition without the sulfur.
The sulfur content of free-machining steels will range from 0.07-0.12% as high as 0.24-0.33%. The amount of sulfur is specified in the AISI or other specifications for carbon steels. Sulfur is not added to any of the alloy steels. Leaded grades comparable to 12L14 and 11L18 are available.
Unless the correct welding procedure is used, the weld deposits on free-machining steel will always be porous and will not provide properties normally expected of a steel of the analysis but without the sulfur or lead.
The basis for establishing a welding procedure for free-machining steels is the same as that required for carbon steels of the same analysis. These steels usually run from 0.010% carbon to as high as 1.0% carbon. They may also contain manganese ranging from 0.30% to as high as 1.65%. Therefore, the procedure is based on these elements. If the steels are free-machining and contain a high percentage of sulfur the only change in procedure is to change to a low-hydrogen type weld deposit.
In the case of shielded metal arc welding this means the use of low-hydrogen type electrode of the E-XX15, E-XX16, or the E-XXX8 classification. In the case of gas metal arc welding or flux-cored arc welding the same type of filler metal is specified as is normally used since these are no-hydrogen welding processes.
Submerged arc welding would not normally be used on free-machining steels. Gas tungsten arc welding is not normally used since free-machining steels are used in thicker sections which are not usually welded with the GTAW process.

Manganese Steel
Manganese steel is sometimes called austenitic manganese steel because of its metallurgical structure. It is also called Hadfield manganese steel after its inventor. It is an extremely tough, nonmagnetic alloy. It has an extremely high tensile strength, a high percentage of ductility, and excellent wear resistance. It also has a high resistance to impact and is practically impossible to machine.
Hadfield manganese steel is probably more widely used as castings but is also available as rolled shapes. Manganese steel is popular for impact wear resistance. It is used for railroad frogs, for steel mill coupling housings, pinions, spindles, and for dipper lips of power shovels operating in quarries. It is also used for power shovel track pads, drive tumblers, and dipper racks and pinions.
The composition of austenitic manganese is from 12-14% manganese and 1-1.4% carbon. The composition of cast manganese steel would be 12% manganese and 1.2% carbon. Nickel is oftentimes added to the composition of the rolled manganese steel.
A special heat treatment is required to provide the superior properties of manganese steel. This involves heating to 1850°F (1008°C) followed by quenching in water. In view of this type of heat treatment and the material toughness, special attention must be given to welding and to any reheating of manganese steel.
Manganese steel can be welded to itself and defects can be weld repaired in manganese castings. Manganese steel can also be welded to carbon and alloy steels and weld surfacing deposits can be made on manganese steels.
Manganese steel can be prepared for welding by flame cutting; however, every effort should be made to keep the base metal as cool as possible. If the mass of the part to be cut is sufficiently large it is doubtful if much heat will build up in the part sufficient to cause embrittlement. However, if the part is small it is recommended that it be frequently cooled in water or, if possible, partially submerged in water during the flame cutting operation. For removal of cracks the air carbon arc process can be used. The base metal must be kept cool. Cracks should be completely removed to sound metal prior to rewelding. Grinding can be employed to smooth up these surfaces.
There are two types of manganese steel electrodes available. Both are similar in analysis to the base metal but with the addition of elements which maintain the toughness of the weld deposit without quenching. The EFeMn-A electrode is known as the nickel manganese electrode and contains from 3-5% nickel in addition to the 12-14% manganese. The carbon is lower than normal manganese ranging from 0.50 to 0.90%. The weld deposits of this electrode on large manganese castings will result in a tough deposit due to the rapid cooling of the weld metal.
The other electrode used is a molybdenum-manganese steel type EFeMn-B. This electrode contains 0.6-1.4% molybdenum instead of the nickel. This electrode is less often used for repair welding of manganese steel or for joining manganese steel itself or to carbon steel. The manganese nickel steel is more often used as a buildup deposit to maintain the characteristics of manganese steel when surfacing is required.
Stainless steel electrodes can also be used for welding manganese steels and for welding them to carbon and low-alloy steels. The 18-8 chrome-nickel types are popular; however, in some cases when welding to alloy steels the 29-9 nickel is sometimes used. These electrodes are considerably more expensive than the manganese steel electrode and for this reason are not popular.

Silicon Steels
Silicon steels or, as they are sometimes called, electrical steels, are steels that contain from 0.5% to almost 5% silicon but with low carbon and low sulfur and phosphorous. Silicon steel is primarily provided as sheet or strip so that it can be punched or stamped to make laminations for electrical machinery.
The silicon steels are designed to have lower hysteresis and eddy current losses than plain steel when used in magnetic circuits. This is a particular advantage when used in alternating magnetic fields. Their magnetic properties make silicon steels useful in direct current fields for most applications.
Silicon steel stampings are used in the laminations of electric motor armatures, rotors, and generators. They are widely used in transformers for the electrical power industry and for transformers, chokes, and other components in the electronics industry.
Welding is important to silicon steels since many of which are welded together. Welds are made on the edge of each sheet to hold the stack together. Welding is done instead of punching holes and riveting the laminations in order to reduce manufacturing costs. Almost all of the arc welding processes are used, submerged arc, shielded metal arc, gas metal arc, gas tungsten arc and plasma arc welding. The more popular processes are gas metal arc using CO2 for gas shielding and the gas tungsten arc process. The plasma arc process is used for some of the smaller assemblies.
When the consumable electrode processes are used the stampings are usually indented to allow for deposition of filler metal. For gas tungsten arc and plasma arc the filler metals are not used and the edges are fused. The size of the weld bead should be kept at minimum so that eddy currents are not conducted between laminations in the electrical stack.
One precaution that should be taken in welding silicon steel laminations is to make sure that the laminations are tightly pressed together and that all of the oil used for protection and used in manufacturing is at a minimum. Oil can cause porosity in the welds which might be detrimental to the lamination assembly.

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Abstract:

Tools and dies do wear and are damaged but by means of welding they can be repaired and reworked and returned to service. In addition, certain kinds of tools and dies can be fabricated by welding. 

In tool and die welding it is not always necessary for the electrode used to provide a deposited weld metal that exactly matches the analysis of the tool steel being welded. It is necessary, however, that the weld metal deposited match the heat treatment of the tool or die steel as closely as possible. Thus, selection of the proper electrode is based on matching the heat treatment of the tool or die steel.

Abstract:

The term cast iron is a rather broad description of many types of irons which are castings but which may have different properties and serve different purposes.
In most welding processes the heating and cooling cycle creates expansion and contraction, which sets up tensile stresses during the contraction period. For this reason, gray cast iron is difficult to weld without special precautions. On the other hand, the ductile cast irons such as malleable iron, ductile iron, and nodular iron can be successfully welded. For best results, these types of cast irons should be welded in the annealed condition.

The term cast iron is a rather broad description of many types of irons which are castings but which may have different properties and serve different purposes. In general, a cast iron is an alloy of iron, carbon, and silicon in which more carbon is present than can be retained in solid solution in austenite at the Eutectic temperature.
The amount of carbon is usually more than 1.7% and less than 4.5%. There are many types of cast iron; in fact, pig iron, which is the product of the blast furnace, can be considered cast iron since it is iron cast into pigs or ingots for later remelting and casting into the final form. The most widely used type of cast iron is known as gray iron. Its tonnage production exceeds that of any other cast metal.
Gray iron has a variety of compositions but it is usually such that the matrix structure is primarily pearlite with many graphite flakes dispersed throughout. Gray cast iron is used in the automotive industry for: engine blocks and heads, automatic transmission housings, differential housing, water pump housing, brake drums, and engine pistons. There are exceptions to this but the exceptions are usually aluminum, which is readily identifiable from cast iron.
There are also alloy cast irons which contain small amounts of chromium, nickel, molybdenum, copper, or other elements added to provide specific properties. These usually provide higher strength cast irons. One of the major uses for the higher strength irons is casting automotive crankshafts. These are sometimes called semisteel or proprietary names.
Another alloy iron is the austenitic cast iron which is modified by additions of nickel and other elements to reduce the transformation temperature so that the structure is austenitic at room or normal temperatures. Austenitic cast irons have a high degree of corrosion resistance.
White cast iron is another type of iron, in which almost all the carbon is in the combined form. This provides a cast iron with higher hardness which is used for abrasion resistance.
Another class of cast iron is called malleable iron. This is made by giving white cast iron a special annealing heat treatment to change the structure of the carbon in the iron. By so doing, the structure is changed to pearlitic or ferritic which increases its ductility.
There are two other classes of cast iron which are more ductile than gray cast iron. These are known as nodular iron and ductile cast iron. These are made by the addition of magnesium or aluminum which will either tie up the carbon in a combined state or will give the free carbon a spherical or nodular shape rather than the normal flake shape in gray cast iron. This structure provides a greater degree of ductility or malleability of the casting.
The gray cast iron has a very low ability to bend and low ductility. Possibly a maximum of 2% ductility will be obtained in the extreme low carbon range. The low ductility is due to the presence of the graphite flakes which act as discontinuities.
In most welding processes the heating and cooling cycle creates expansion and contraction, which sets up tensile stresses during the contraction period. For this reason, gray cast iron is difficult to weld without special precautions. On the other hand, the ductile cast irons such as malleable iron, ductile iron, and nodular iron can be successfully welded. For best results, these types of cast irons should be welded in the annealed condition.

Preparation for Welding
In preparing the casting for welding it is necessary to remove all surface materials to completely clean the casting in the area of the weld. This means removing paint, grease, oil, and other foreign material from the weld zone. It is desirable to heat the weld area for a short time to remove entrapped gas from the weld zone of the base metal.
Where grooves are involved a V groove from a 60-90° included angle should be used. Complete penetration welds should always be used since a crack or defect not completely removed may quickly reappear under service conditions.
Preheating is desirable for welding with any of the welding processes. It can be reduced when using extremely ductile filler metal. Preheating will reduce the thermal gradient between the weld and the remainder of the case iron. Preheat temperatures should be related to the welding process, the filler metal type, the mass and the complexity of the casting.

Arc Welding
The shielded metal arc welding process can be utilized for welding cast iron. There are four types of filler metals that may be used: cast iron covered electrodes, covered copper base alloy electrodes, covered nickel base alloy electrodes and mild steel covered electrodes. There are reasons for using each of the different specific types of electrodes as follows: the machinability of the deposit, the color match of the deposit, the strength of the deposit, and the ductility of the final weld.
When arc welding with the cast iron electrodes, preheat to between 120° and 425°C is necessary, depending on the size and complexity of the casting and the need to machine the deposit and adjacent areas. In general, it is best to use small-size electrodes and a relatively low current setting. A medium arc length should be used and if at all possible welding should be done in the flat position.
There are two types of copper-base electrodes, the copper tin alloy (ECuSn-A and C) and the copper aluminum (ECuAl-A2) types. The copper zinc alloys cannot be used for arc welding electrodes because of the low boiling temperature of zinc. Zinc will volatilize in the arc and will cause weld metal porosity. The copper tin electrodes will produce a braze weld having good ductility. The ECuSn-A has less amount of tin. It is more of a general purpose electrode. The ECuSn-C provides a stronger deposit with higher hardness.
The copper aluminum alloy electrode (ECuAl-A2) provides much stronger welds and is used on the higher strength alloy cast irons.
When the copper base electrodes are used, a preheat of 120-200°C is recommended and small electrodes and low current should be used. The welding technique should be to direct the arc against the deposited metal or puddle to avoid penetration and mixing the base metal with the weld metal. Slow cooling is recommended after welding. The copper-base electrodes do not provide a good color match.
There are three types of nickel electrodes used for welding cast iron. The ENiFe-CI contains approximately 50% nickel with iron, the ENiCI contains about 85% nickel and the ENiCu type contains nickel and copper. The ENiFeCI electrode is less expensive and provides results approximately equal to the high-nickel electrode. These electrodes can be used without preheat; however, heating to 40°C is recommended. The nickel and nickel iron deposits are extremely ductile and will not become brittle with the carbon pickup. The hardness of the heat-affected zone can be minimized by reducing penetration into the cast iron base metal. The copper nickel type comes in two grades; the ENiCu-A with 55% nickel and 40% copper and the ENiCu-B with 65% nickel and 30% copper. Either of these electrodes can be used in the same manner as the nickel or nickel iron electrode with about the same technique and results. The deposits of these electrodes do not provide a color match.
Mild steel electrodes (E St) are not recommended for welding cast iron if the deposit is to be machined. The mild steel deposit will pick up sufficient carbon to make a high-carbon deposit which is impossible to machine. Additionally, the mild steel deposit will have a reduced level of ductility as a result of increased carbon content. This type of electrode should be used only for small repairs and should not be used when machining is required.
Minimum preheat is possible for small repair jobs. Here again, small electrodes at low current are recommended to minimize dilution, and to avoid the concentration of shrinkage stresses. Short welds using a wandering sequence should be used and the weld should be peened as quickly as possible after welding. The mild steel electrode deposit provides a fair color match.

Oxy-Fuel Gas Welding
The oxy-fuel gas process is often used for welding cast iron. Most of the fuel gases can be used. The flame should be neutral to slightly reducing. Flux should be used. Two types of filler metals are available: The cast iron rods (RCI and A and B) and the copper zinc rods (RCuZn-B and C).
Welds made with the proper cast iron electrode will be as strong as the base metal. The RCI classification is used for ordinary gray cast iron. The RCI-A has small amounts of alloy and is used for the high strength alloy cast irons and the RCI-B is used for welding malleable and nodular cast iron. Good color match is provided by all of these welding rods. The optimum welding procedure should be used with regard to joint preparation, preheat, and post heat.
The copper zinc rods produce braze welds. There are two classifications: RCuZn-B, which is a manganese bronze and RCuZn-C, which is a low-fuming bronze. The deposited bronze has relatively high ductility but will not provide a color match.

Gas Metal Arc Welding
The gas metal arc welding process can be used for making welds between malleable iron and carbon steels. Several types of electrode wires can be used, including:

• Mild Steel (E70S-3) using 75% Argon + 25% CO2 for shielding.
• Nickel Copper (ENiCu-B) using 100% Argon for shielding.
• Silicon Bronze (ECuZn-C) using 50% Argon +50% Helium for shielding.

In all cases small diameter electrode wire should be used at low current. With the mild steel electrode wire the Argon-CO2 shielding gas mixture is used to minimize penetration. In the case of the nickel base filler metal and the copper base filler metal the deposited filler metal is extremely ductile. The mild steel provides a fair color match. A higher preheat is usually required to reduce residual stresses and cracking tendencies.

Flux-Cored Arc Welding
This process has recently been used for welding cast irons. The more successful application has been using a nickel base flux-cored wire which produces a weld metal deposit very similar to the 50% nickel deposit provided by the ENiFe-CI covered electrode. This electrode wire is normally operated with CO2 shielding gas but when lower mechanical properties are not objectionable it can be operated without external shielding gas. The minimum preheat temperatures can be used. The technique should minimize penetration into the cast iron base metal. Postheating is normally not required. A color match is not obtained.
Flux-cored self-shielding electrode wires (E60T-7), operating with electrode negative (straight polarity), have also been used for certain cast iron to mild steel applications. In this case, a minimum penetration type weld is obtained and by the proper technique penetration should be kept to a minimum. It is not recommended for deposits that must be machined.

Other Processes
Other welding processes can also be used for cast iron. Thermit welding has been used for repairing certain types of cast iron machine tool parts. The procedure is identical to that used for welding steel except that a special thermit mixture is required.
Soldering can be used for joining cast iron and is sometimes used for repairing small defects in small castings. Soldering is done with an iron or with a torch. Flash welding can also be used for welding cast iron.

Abstract:

Welding, which is one of the newer metalworking trades, can trace its historic development back to ancient times.
The earliest example comes from the Bronze Age. Small gold circular boxes were made apparently by pressure welding lap joints together. It is estimated that these boxes were made more than 2,000 years ago and are presently on exhibit at the National Museum in Dublin, Ireland.

Welding, which is one of the newer metalworking trades, can trace its historic development back to ancient times. The earliest example comes from the Bronze Age. Small gold circular boxes were made apparently by pressure welding lap joints together. It is estimated that these boxes were made more than 2,000 years ago and are presently on exhibit at the National Museum in Dublin, Ireland.
During the Iron Age it appears that the Egyptians and other people in the Eastern Mediterranean area learned to weld pieces of iron together. Many tools and weapons have been found which were apparently made approximately 1000 B.C. Items of this type are on exhibit in the British Museum in London. Other examples of early welded art are displayed in the museums of Philadelphia and Toronto. Items of iron and bronze that exhibit intricate forging and forge welding operations have been found in the pyramids of Egypt.
During the Middle Ages the art of blacksmithing was developed to a high degree and many items of iron were produced which were welded by hammering. One of the largest welds from this period was the Iron Pillar of Delhi in India, which was erected about the year 310 A.D.
Sir Humphrey Davies of England is credited with providing a foundation for modern welding with two of his discoveries. One was the discovery of acetylene and the second was the production of an arc between two carbon electrodes using a battery. In the mid-1800s, the electric generator was invented and arc lighting became popular.
The period of 1877 to 1903 provided a great number of discoveries and inventions pertaining to welding. During this period gas welding and cutting were developed. Arc welding with the carbon arc and metal arc was developed and resistance welding, much as it is known today, became a practical joining process.
This work was the actual beginning of arc welding or at least carbon arc welding. Benardos’ efforts were apparently all restricted to carbon arc welding, although he was able to weld iron as well as lead. Carbon arc welding became increasingly popular during the late 1890s and early 1900s.
Apparently Benardos was not successful with a metallic electrode, and in 1892 C.L. Coffin of Detroit was awarded the first U.S. patent for an arc welding process using a metal electrode. This was the first record of the metal melted from the electrode actually carried across the arc to deposit filler metal in the joint to make a weld. At about the same time, N. G. Slavianoff, a Russian, presented the same idea of transferring metal across an arc, but to cast metal in a mold.
In about 1900 Strohmeyer introduced a coated metal electrode in Great Britain. There was a thin wash coating of clay or lime, but it did provide a more stable arc. Meanwhile, the resistance welding processes were developed, including spot welding, seam welding, projection welding, and flash butt welding. Professor Elihu Thompson is given credit for originating resistance welding. Thermit welding was invented by a German named Goldschmidt in 1903 and was used to weld railroad rail.
Gas welding and cutting were also perfected in this same period. The production of oxygen, and later the liquefying of air, along with the introduction in 1887 of a blow pipe or torch, helped the development of both welding and cutting. Before 1900 hydrogen and coal gas were used with oxygen. However, in about 1900 a torch suitable for use with low-pressure acetylene was developed and the oxyacetylene gas welding and cutting processes were launched.
During the period of about 1900 to 1918, the oxyacetylene welding and cutting process plus the carbon arc welding and metal arc welding process with lightly covered electrodes were used primarily for repair and maintenance work.
World War I brought a tremendous demand for metal material production, and welding was pressed into service. Many companies sprang up in America and in Europe to manufacture various types of welding machines and electrodes to meet this requirement.
Immediately after the war, in 1919, twenty members of the Wartime Welding Committee of the Emergency Fleet Corporation, under the leadership of Comfort Avery Adams, founded the American Welding Society. It was founded as a nonprofit organization dedicated to the advancement of welding and allied processes.
In 1920, automatic welding was introduced. It utilized bare electrode wire operated on direct current and utilized arc voltage as the basis of regulating the feed rate of the electrode wire. It was used to build up worn motor shafts and worn crane wheels. It was also used by the automobile industry to produce rear axle housings.
During the 1920s various different grades and types of welding electrodes were developed and made available. Mild steel or low carbon steel, usually with a carbon of 0.20% or less, was used for welding practically all grades of rolled steel. Higher carbon electrodes and alloy steel electrodes were also developed. Copper alloy rods were developed for carbon arc welding and brazing.
There was considerable controversy during the 1920s about the advantage of the heavy-coated rods versus light- or wash-coated rods. Heavy-coated rods made by dipping were more expensive. Coating applied by extrusion on the rod was less expensive.
During the 1920s there was considerable interest in shielding the arc and weld area by externally applied gases. It was realized that the atmosphere of oxygen and nitrogen in contact with the molten weld metal caused brittle and sometimes porous welds. In view of this, research work was done to utilize gas-shielding techniques. They utilized two electrodes starting with carbon electrodes but later changing to tungsten electrodes.
The hydrogen was changed to atomic hydrogen in the arc. It was then blown out of the arc forming an intensely hot flame of atomic hydrogen burning to the molecular form and liberating heat. This arc produced half again as much heat as an oxyacetylene flame. This was named the atomic hydrogen welding process. Atomic hydrogen never became extremely popular but was used during the 1930s and 1940s for special applications of welding and later on for welding of tool steels.
The covered electrode became the mainstay of the welding industry, even though it was applied manually. At the same time many efforts were made to improve automatic welding utilizing bare wire. Such efforts included the use of a covering on electrodes which were then coiled and at the welding point the coating was milled away to introduce welding current to the core wire.
One of the more specialized welding processes was developed in 1930 at the New York Navy Yard. This process, known as stud welding, was developed specifically for attaching wood decking over a metal surface. The process welded studs, screws, etc., to the base metal by means of a special gun, which automatically controlled the arc. Fluxing elements on the end of the stud improved the properties of the weld. Stud welding became popular in the shipbuilding and construction industries and in manufacturing.
The automatic process that became extremely popular was the submerged arc welding process. This "under powder" or smothered arc welding process was developed by the National Tube Company for a new pipe mill at McKeesport, Pennsylvania. It was designed to make the longitudinal seams in the pipe. Submerged arc welding was used during the defense buildup in the late 1930s and early 1940s in both the shipyards and in ordnance factories. It is one of the most productive welding processes and remains popular today.
Gas tungsten arc welding had its beginnings from an idea by C.L. Coffin to weld in a nonoxidizing gas atmosphere, which he patented in 1890. The concept was further refined in the late 1920s by Hobart, when he used helium for shielding, and Devers, who used argon.
The other concept invented by Hobart and Devers was the gas shielded metal arc welding process successfully developed at Battelle Memorial Institute in 1948 under the sponsorship of the Air Reduction Company. This development utilized the gas-shielded arc similar to the gas tungsten arc, but replaced the tungsten electrode with a continuously fed electrode wire.
In 1953 Lyubavskii and Novoshilov announced the use of welding with consumable electrodes in an atmosphere of CO2 gas. The CO2 welding process immediately gained favor since it utilized equipment developed for inert gas metal arc welding but could now be used for economically welding steels. The CO2 arc is a hot arc and the larger electrode wires required fairly high currents. Efforts were made to make the process more acceptable for the welder and this in turn led to smaller diameter electrode wires and refined power supplies.
Another variation was the use of inert gas with small amounts of oxygen which provided the spray-type arc transfer. This variation became popular in the early 1960s for welding agricultural equipment. The latest variation of gas metal arc welding is the use of pulsed current.
Soon after the introduction of the CO2 welding process a variation utilizing a special electrode wire was developed. This wire, described as an inside-outside electrode, was tubular in cross section with the fluxing agents on the inside. These wires could be used in the same equipment as the gas metal arc welding process.
The plasma arc welding process, which is very similar to gas tungsten arc welding, was invented by Robert Gage in 1957. Plasma arc welding uses a constricted arc or an arc through an orifice, which creates an arc plasma that has a higher temperature than the tungsten arc. It is also used for metal spraying and for cutting. As a cutting process it became popular for nonferrous metals. It is used for spraying both wires and powders. Plasma arc welding is popular for low-current welding and is becoming increasingly popular in higher-current applications.
The electron beam welding process, which uses a focused beam of electrons as a heat source in a vacuum chamber, was developed in Germany and France. The Zeiss Company and the French Atomic Energy Commission are credited with developing the process in the late 1940s. In the last few years the process has gained widespread acceptance for welding. Its popularity is increasing since recent developments have allowed it to be taken out of the vacuum chamber which was its major disadvantage. More and more applications are being found for this process, which should grow in popularity in the future.
Friction welding, which uses high rotational speeds and upset pressure to provide friction heat, was developed in the Soviet Union, but additional work was done in Great Britain and the USA. It is a specialized process and has applications only where a sufficient volume of similar parts are to be welded because of the initial expense of equipment and tooling. This process, also called inertia welding, will find more uses and will become more popular.
A more recent welding process is laser welding. The laser originally developed at the Bell Telephone Laboratories was used as a communications device. Because of the tremendous concentration of energy in a small space it proved to be a powerful heat source. It has been used for cutting metals and other materials. The early problems involved short pulses of energy; however, today continuous pulse type equipment is available. The equipment is still extremely expensive and bulky, but in time it should be reduced in cost and size. The laser is now finding welding applications in routine metalworking operations.
There are many other variations of these processes, which are not specifically processes themselves. These will be discussed along with the basic process. Undoubtedly, additional welding processes and methods will be developed and as the need arises they will be adapted to metalworking requirements.

Abstract:

Concrete reinforcing bars, or as they are more technically known, deformed steel reinforcing bars, are used in reinforced concrete construction. This includes buildings, bridges, highways, locks, dams, docks, piers, etc.
Welding is finding increasing importance for splicing concrete reinforcing bars. Three welding processes are used for the majority of welding splices; however, several of the other processes can be used.

Concrete reinforcing bars, or as they are more technically known, deformed steel reinforcing bars, are used in reinforced concrete construction. This includes buildings, bridges, highways, locks, dams, docks, piers, etc. The principle applications of reinforcing bars include reinforcement of columns, girders, beams, slabs, pavements, as well as precast and prestressed concrete structures.
Concrete is strong in compression and shear but is weak in tension. By using deformed steel reinforcing bars imbedded in the concrete, tensile stresses can be accommodated, thus reinforced concrete provides compression strength of concrete and tensile strength of steel.
It is necessary, however, that the concrete and steel work together. This is accomplished by means of a bond between the bar and the concrete which is achieved by means of deformations which are rolled into the bars. These deformations keep the bars from slipping through the concrete.
Concrete reinforcing bars come in different sizes which are designated by a series of numbers. The numbers assigned to bars are based on the number of 1/8 inches included in the nominal diameter. The nominal diameter of a deformed reinforcement bar is equivalent to the diameter of a plain steel bar having the same weight per foot as the deformed bar.
There are three ASTM specifications for reinforcing bars:
 
  A 615, plain billet steel bars;
  A 616, rail steel reinforcing bars; and
  A 617, axle steel reinforcement bars.
All of the reinforcing bars produced in the USA are identified by markings rolled into the bar. These markings will show, by means of raised letters, the code for the manufacturer of the steel bar. This is then followed by the letter identifying the specific steel mill where the bar was produced, based on standard designations. The next symbol indicates the bar size by the bar number. The next symbol indicates the type of steel as follows: N indicates new billet steel, A indicates axle steel, and the third symbol which is a cross section of a railroad rail indicates that the bar was rerolled from used railroad rails.
The next identification symbol is a number indicating the grade of the steel. If there is no number it normally means it is the minimum grade within the specification. Grades are also identified by a single or double continuous longitudinal line through at least five spaces offset from the center of the bar. A single line indicates the middle-strength grade and a double line indicates the highest-strength grade. It is important to determine the type of steel and the grade since this will be valuable information in establishing the welding procedure.
The specifications do not include chemical requirements for the different classes; however, when bars are purchased from the mill, the mill will provide a chemical analysis report of the bars, if requested. The grade number is the indication of the strength of the bars and the numbers indicate the yield point in thousand pounds per square inch minimum.
It is necessary to splice concrete reinforcing bars in all but the most simple concrete structures. In the past, splicing was done by overlapping the bars from 20 to 40 diameters and wiring them together and relying on the surrounding concrete to transmit the load from one bar to the other. This method is wasteful of the steel and is sometimes impractical. An example of this occurs when splices must be made in heavily reinforced columns. The close spacing of the bars makes lap splicing particularly difficult and often requires a larger column diameter to provide sufficient concrete between bars and covering the bars.
Welding is thus finding increasing importance for splicing concrete reinforcing bars. Three welding processes are used for the majority of welding splices; however, several of the other processes can be used. There is a mechanical splice similar to welding which utilizes medium-strength metal cast metallic grout around the ends of the bars enclosed within a steel sleeve having internal grooves.
The welding processes most commonly used are the shielded metal arc welding process, the gas metal arc welding process, and the thermit welding process.
There are no chemistry requirements for the three ASTM specifications. However, the reinforcing bars of specification A 616 rail steel are produced from used railroad rails which were originally made to specification A 1. Old railroad rails are salvaged and heated and cut into three parts, the flange, the web, and the head. The heads are then rolled into the deformed reinforcing bars. ASTM specification A 1 has chemical requirements for steel rails and they contain relatively high amounts of carbon and manganese.
The reinforcing bars made to specification A 617 are made from salvaged carbon steel axles used for railroad cars. These axles when originally produced were made to specification A 21. In this ASTM specification the carbon and manganese is relatively high. These are both considered in the hard-to-weld category of steels.
The bars produced to A 615 have only a maximum for phosphorous content; however, based on the strength level of steels the alloy content should not be too high. For quality welding it is best to assume that they, too, are in the hard-to-weld category. If at all possible, the analysis of the reinforcing bars should be determined from mill reports. If this is not possible the bars could be analyzed for exact composition. It is recommended that the bars be considered to have a carbon equivalent of 0.75, thus in the hard-to-weld category.
The American Welding Society has provided a specification entitled, "Reinforcing Steel Welding Code". This code provides a table of carbon equivalents which relates to the bar size and then presents recommended preheat and interpass temperature. The standard formula for the determination of carbon equivalent is used. There are six carbon equivalents which can only be calculated if the analysis of the reinforcing bars are known.
The code also provides joint design information for making direct butt splices, for making indirect butt splices, and for making lap splices. A butt splice is a direct end-to-end splice of bars with their axis approximately in line and of approximately the same size. An indirect butt splice is one in which an intermediary piece such as a steel plate or rolled angle is used with each reinforcing bar welded directly to the same piece.
The lap welded splice is made by overlapping the two bars alongside each other and welding together. For butt splices when the bars are in the horizontal position the single groove weld is most often used with a 45° to 60° included angle. Double groove welds can be made in the larger size bars. When the bars are to be welded with the axis vertical a single or double bevel groove weld is used with the flat side or horizontal side on the lower bar. On occasion, the reinforcing bar may need to be welded to other steel members and a variety of weld joints can be used.
This code provides filler metal selection information based on the grade number of the steel. When welding using the shielded metal arc welding process, Grade 40, the AWS E-7018 would be recommended, for Grade 50 the AWS E-8018 would be recommended, for Grade 60 and the low-alloy A706 the AWS E-9018 electrode is recommended, and for the Grade 75 the AWS E-10018 electrode would be recommended.
If the XXI8 is not available the XX15 or XX16 can be used. In the case of gas metal arc welding, the E-70S electrode would be used and for flux-cored arc welding the E70T type would be used when welding Grade 40 bars. There are no filler metal specifications for the higher levels of gas metal arc welding electrodes or flux-cored arc welding electrodes at this time. If these processes are to be used the filler metal would need to meet the same mechanical properties as the equivalent shielded metal arc welding electrode mentioned.
The code also provides minimum preheat and inner-pass temperatures based on the carbon equivalent of the reinforcing bars. It also relates to the size of the bar. It is therefore important to determine the composition of the bar so that carbon equivalent can be determined. In the case of large bars and if the carbon equivalent is not known the 500° preheat would be recommended.
The code further requires that joint welding procedures should be established based on the welding process, filler metal type and size, and welding technique, which involves position, joint detail, etc.
Welders must be qualified. A direct butt splice or indirect butt splice specimen is used. The gas metal arc welding process will make the weld in approximately one-half the time required for shielded metal arc covered electrodes. In either case, however, or with the flux-cored arc welding process, the welds will develop strengths equal or exceeding the specified yield strength of the reinforcing steel bars.
Welding is highly recommended as the way to splice reinforcing bars since the concrete will fail at values substantially below the yield strength of the reinforcing bars. This means that the strength of the welds will exceed the requirements for most applications. In any case, the welded splices will exceed the strength of lapped and wired splices. It will also exceed a strength level of the cast metal splices which are sufficiently strong to withstand the strength level of the reinforced concrete composite structure.

Abstract:

Welding of zinc-coated steel can be done, but specific precautions should be taken. When galvanized steel is arc welded the heat of the welding arc vaporizes the zinc coating in the weld area. This is because the boiling point of zinc is below the melting point of steel. The zinc volatilizes and leaves the base metal adjacent to the weld.
When galvanized sheet is resistance welded, the welding heat causes less disturbance of the zinc coating than the arc processes. Resistance welding of galvanized steel is, however, more of a problem than arc welding.

There are many types of coated steels and some of them are welded. For example, tern plate steel, which is tin-lead coated, and aluminized steel. Steels coated with tin, cadmium, copper, and lead may be soldered.
Galvanized steel is widely used and is becoming increasingly important. Manufacturers of many items such as truck bodies, buses, and automobiles are increasingly concerned with the effects of corrosion particularly when chemicals are used on roads for ice control. Galvanized metal is also used in many appliances such as household washing machines and driers and in many industrial products such as air conditioning housings, processing tanks, etc. Other uses for galvanized products are for high tension electrical transmission towers, highway sign standards, and protective items.
There are two basic methods of galvanizing steel. One is by coating sheet metal and the other is by hot dipping the individual item. The coated sheet metal is produced by the continuous hot dip process, but traffic control devices, high-tension transmission tower parts, etc., are made by dipping each item. The continuous hot dip or zinc coated sheet comes in eight classes based on the thickness of the zinc coating.
Welding of zinc-coated steel can be done, but specific precautions should be taken. When galvanized steel is arc welded the heat of the welding arc vaporizes the zinc coating in the weld area. This is because the boiling point of zinc (1600°F, 871°C) is below the melting point of steel (2800°F, 1538°C). The zinc volatilizes and leaves the base metal adjacent to the weld. The extent to which the coating is disturbed depends on the heat input of the arc and the heat loss from the base metal. The disturbed area is greater with the slower welding speed processes such as oxyacetylene welding or gas tungsten arc welding.
When galvanized sheet is resistance welded, the welding heat causes less disturbance of the zinc coating than the arc processes. The resistance to corrosion or rather the protection by the zinc is not disturbed since the zinc forced from the spot weld will solidify adjacent to the spot weld and protect the weld nugget. Resistance welding of galvanized steel is, however, more of a problem than arc welding.

Weld Quality
The low boiling temperature of the zinc of the coating causes it to volatilize in the heat produced by an arc or by an oxyacetylene flame. The zinc in the gaseous state may become entrapped in the molten weld metal as it solidifies. If this occurs there will be porosity in the weld metal and if sufficient zinc is available it will cause large voids in the surface of the deposit.
The presence of the zinc in stressed welds can cause cracking and it may also cause delayed cracking due to stress corrosion. To eliminate this, the weld joint must be designed to allow the zinc vapor to completely escape from the joint. Fixturing, backing straps, etc., should be arranged to allow for the zinc to completely escape. Other ways to avoid zinc entrapment in weld metal is to use sufficient heat input when making the weld.
It is also important to secure complete and full penetration of the joint. The ultimate precaution would be to remove the zinc from the area to be welded.
When welding on galvanized steel or any coated steel, particularly those with coatings that produce noxious fumes, positive ventilation must be provided. Positive ventilation involves the use of a suction hose at the weld area. When using the gas metal arc process or the flux-cored arc process, the suction type gun nozzles should be used. Welding on zinc or other coated steels should never be done in confined areas.
For corrosion resistance of the weld it is sometimes advisable to use a corrosion-resistant weld metal. This can be done by using a bronze deposit such as a copper-zinc alloy, or a stainless steel electrode. In any case, when arc or oxyacetylene welding is used the area adjacent to the weld will lose the protective zinc coating which must be repaired.

Arc Welding
When using covered electrodes, the electrode selection should be based on the thickness of metal and the position that will be used when welding galvanized steel. The E-XX12 or 13 will be used for welding thinner material, the E-XX10 or 11 will be used for welding galvanized pipe and for welding hot-dipped galvanized parts of heavier thickness. The low-hydrogen electrodes can also be used on heavier thicknesses.
The welding technique should utilize slow travel speed to permit degassing of the molten metal. The electrode should point forward to force the zinc vapor ahead of the arc. The quality of welds will be equal to those of bare metal, assuming the weldability of the steel is equal.
The gas metal arc welding process is becoming more widely used for joining galvanized steel. For the thinner gauges the fine-wire short-circuiting method is recommended. In this case, the technique would be similar to that used for bare metal. The shielding gas can be 100% CO2 or the 75% argon and 25% CO2 mixture. The selection is dependent primarily on the material thickness and position of welding.
For certain applications, the argon-oxygen mixture is used. The amount of spatter produced when welding galvanized steel is slightly greater than when welding bare steel. The flux-cored arc welding process can be used as easily as gas metal arc welding for galvanized steel. It is recommended for the heavy gauges and on hot-dipped galvanized parts. The highly deoxidized type of welding electrode should be used.
The gas tungsten arc welding process is not popular for welding galvanized steel, since it is one of the slower welding processes and does cause a larger area of zinc adjacent to the weld to be destroyed. In addition, the volatilized zinc is apt to contaminate the tungsten electrode and require frequent redressing of the electrode.
In an effort to overcome this, extra high gas flow rates are sometimes used, which can be expensive. Other techniques may be used as well. If a filler rod is used it may be of either the highly deoxidized steel type or of the bronze type previously mentioned. In this case the arc is played on the filler rod and zinc contamination of the tungsten electrode is avoided.
The carbon arc welding process has been widely used for welding galvanized steel. Both the single carbon torch and twin carbon torch can be used. The twin carbon torch is used as a source of heat much the same as the oxyacetylene flame; however, when the single carbon is used the carbon can be played on the filler rod and extremely high rates of speed can be accomplished. Normally in this situation the filler rod, Type RBCuZn-A (60% Cu-40% Zn). By directing the arc on the filler rod it melts and sufficient heat is produced in the base metal for fusion but not sufficient to destroy the zinc coating. This process and technique is widely used in the sheet metal duct work industry.

Torch Brazing
The oxyacetylene torch is also widely used for brazing galvanized steel. The technique is similar to that mentioned with the carbon arc. The torch is directed toward the filler rod which melts and then fills the weld joint. A generous quantity of brazing flux is used and this helps reduce the zinc loss adjacent to the weld.

Repairing the Zinc Coating
The area adjacent to the arc or gas weld will be free of zinc because of the high temperature of the weld. To produce a corrosion-resistant joint, the zinc must be replaced in this area and on the weld itself unless the nonferrous filler metal was used.
There are several ways of replacing the zinc. One is by the use of zinc base paste sticks sometimes called zinc sticks or galvanized sticks sold under different proprietary names. These sticks are wiped on the heated bare metal. With practice a very good coating can be placed which will blend with the original zinc coating. This coating will be thicker than the original coating, however.
Another way of replacing the depleted zinc coating is by means of flame spraying using a zinc spray filler material. This is a faster method and is used if there is sufficient zinc coating to be replaced. The coating should be two to two-and-one-half times as thick as the original coating for proper corrosion protection.

Other Coated Metals
One other coated metal that is often welded is known as tern plate. This is sheet steel hot dipped with a coating of a lead-tin alloy. The tern alloy is specified in thicknesses based on the weight of tern coating per square foot of sheet metal. Tern plate is often used for making gasoline tanks for automobiles. It is thus welded most often by the resistance welding process. If it is arc welded or oxyacetylene welded the tern plating is destroyed adjacent to the weld and it must be replaced. This can be done similar to soldering.
Aluminized steel is also widely used in the automotive industry particularly for exhaust mufflers. In this case, a high silicon-aluminum alloy is coated to both sides of the sheet steel by the hot dip method. There are two common weights of coating, the regular is 0.40 ounces per square foot and the lightweight coating is 0.25 ounces per square foot based on coating both sides of the sheet steel. Here again, if an arc or gas weld is made on aluminum-coated steel the aluminum coating is destroyed. It is relatively difficult to replace the aluminum coating and, therefore, painting is most often used.

Abstract:

Shielded metal-arc welding with the transformer welding machine depends upon this fundamental fact: that when one side of the welding circuit is attached to a piece of steel, a welding electrode connected to the other side and the two brought into contact, an arc will be established. If the arc is properly controlled, the metal from the electrode will pass through the arc and be deposited on the steel. When the electrode is moved along the steel at the correct speed, the metal will deposit in a uniform layer called a bead.

Shielded metal-arc welding with the transformer welding machine depends upon this fundamental fact: that when one side of the welding circuit is attached to a piece of steel, a welding electrode connected to the other side and the two brought into contact, an arc will be established. If the arc is properly controlled, the metal from the electrode will pass through the arc and be deposited on the steel. When the electrode is moved along the steel at the correct speed, the metal will deposit in a uniform layer called a bead.
The electrodes used in welding are carefully manufactured to produce strong, sound welds. They consist of a core of steel wire, usually called mild since it contains a low (0.10-0.14) percentage of carbon. Around this core is applied a special coating which assists in creating the arc and at the same time protects the molten steel as it transfers across the arc.
In order to utilize these principles in metal-arc welding, some means of controlling the power is essential. The power in a welding circuit is measured by the voltage and current. However, the voltage is governed by the arc length and in turn depends on the electrode diameter. Therefore, the practical measure of the power, or, heat, is in terms of the current, generally measured in amperes. Obviously a small electrode requires less current than a large one. To simplify operations the scale on the front of the welding machine is marked off for the various current values.
The exact current selected for a job depends upon the size of the pieces to be welded and the position of welding. Generally a lower current will be sufficient for welding on a small part than would be necessary to weld on a large piece of the same thickness. Similarly with a given size of electrode a lower current should be used on thin metals than on the heavier sections.

Striking the Arc - Running Beads
In learning to weld there are certain fundamental steps which must be mastered before one can attempt to weld on actual work. Preparatory to the actual striking of an arc, it is necessary to insert the electrode in the holder. In this method the striking end of the electrode is dragged across the work in a manner much the same as striking a match. When the electrode touches the work, the welding current starts. If held in this position, the electrode would "freeze" or weld itself to the work and to overcome this, the electrode is withdrawn from the work immediately after contact has been made.
The amount that the electrode is withdrawn is small and depends on the diameter; this distance is known as the arc length. If in striking an arc, the electrode freezes, it may be freed by a quick twist of the wrist.
Another method of establishing the arc is available. In this the electrode in the holder is brought straight down on the work and immediately after contact, is withdrawn to the proper arc length. Practice striking the arc using both methods. Generally the scratching method is preferred for a-c welding.
Determination of the correct arc length is difficult since there is no ready means of measuring it. As a preliminary guide, use about 1/16" arc length on 1/16" and 3/32" electrode; for 1/8" and 5/32" electrodes use about 1/8" arc length. When skill is acquired, the sound of the arc will be a good guide. A short arc with correct current will give a sharp, crackling sound. Examination of the deposited bead will give a further check.
Once the knack of starting and holding an arc has been learned, turn next to depositing weld metal. In the beginning it is best to run beads of weld metal on flat plates using a full electrode. Practice moving from left to right and from right to left. The electrode should be held more or less perpendicular to the work, except that tilting it ahead, in the direction of travel will prove helpful.

Weaving
When it is necessary to cover a wider area in one pass of the electrode, a method known as weaving is employed. In this the electrode is moved or oscillated from side to side in a set pattern. In order to be sure of uniform deposits, it is necessary to use a definite pattern. While weaving is helpful, particularly when building up metal, it should be limited to weaves not exceeding 2-1/2 times the diameter of the electrode.

Butt Joints
Up to this point the discussion has covered only the deposit of beads on the flat plates. While such operations are helpful in building up worn parts or applying hard-facing materials, they do not help in learning to weld pieces together. In making bead welds, previously described, it was probably noted that the depositing of weld metal on one side of the plate caused it to "curl" up towards the weld; this is called distortion and will almost always be found when heat is applied locally to a metal plate. Similarly in making a butt weld distortion will cause the edges of the plate to draw together ahead of welding. This is caused by the contraction of the deposited weld metal on cooling. It may be overcome by spreading the edges apart on a long taper of about 1/8" per foot.
In making welds in a butt joint, preparation of the edges may be necessary to insure good results. In metal arc welding it is common practice to weld thin materials up to 3/16" thick without any special preparation using the square groove butt joint. For thickness of 3/16" and over the "V" groove either single or double is employed. Generally the single "V" groove will be satisfactory on thicknesses up to3/4" and in those cases, regardless of thickness, where one can work on the weld from one side only.

Beveling
The best means for beveling steel for welding is by means of the oxyacetylene cutting torch. The work may be done with a hand guided torch or special oxyacetylene cutting machine. However, in performing this cutting, a scale will adhere to the plates. This must be removed by grinding or chipping before welding as it is likely to become entrapped and thus produce an unsound weld. Where oxyacetylene cutting equipment is not available, grinding will probably be the best means of preparing bevels. The angles of these bevels should be about 30 degrees and the bottom edge may be left square for a distance of about 1/16".
Practice making butt welds starting on thin material about 1/8" thick. Avoid very thin material (around 1/16" thick) in the beginning as this requires a fair degree of skill. Separate the squared edges of the 1/8" material about 1/16" and make a butt weld all the way through with a 1/8" electrode.
Probably the first attempts will fail to penetrate the sheet or may burn through. Keep trying by adjusting the current within the recommended range; also vary the travel speed to give the desired weld. Having mastered the 1/8", proceed to a similar exercise on 1/4". This time however deposit a bead on each side of the joint and try to fuse one to the other. Since the weld from one side is in effect on 1/8" thickness, no bevel is needed.
When making practice butt welds it is wise to check the results occasionally. When elaborate testing equipment is not available, this may be done with a hammer and vise. Grip a short, welding piece with the weld just above the jaws. A good weld will not break under this test but will bend over.

Tee and Lap Joints
The other basic type of weld, the fillet weld, is used for making tee and lap joints. For this type of welding no special preparation other than squared edges is necessary.
Considering the tee joint first, it will be seen immediately that the different locations of the pieces creates a problem. The method of holding the electrode for butt welds will not be satisfactory. This will provide fusion into the corner and a fillet, the sides of which will be approximately equal.
For maximum strength a fillet weld should be deposited on each side of the upright the lap joint, while involving the same fundamental weld type, the fillet has metal distributed differently and therefore requires still another technique.

Welding Vertically, Horizontally and Overhead
The importance of welding in the flat position whenever possible cannot be stressed too strongly. The quality of the weld is better, the operation easier and faster. However, occasions will arise when it is necessary to work on parts fixed in position under which condition welds must be deposited horizontally, vertically and overhead. It must be realized at the very beginning that welding in these positions is difficult and will require constant practice to develop skill.
As in the case of welding in the flat position, it is best to start practicing by first running bead welds in the various positions. Then as facility is gained on these operations practice may be continued on butt and fillet welds (tee and lap joints) in these positions.
One of the first facts noted when welding in these positions is that the force of gravity tends to cause the molten metal to drip (fall) down. The technique used, therefore must be designed to overcome this and since it is difficult it is best to approach this by steps. To accomplish this, start by making horizontal bead welds on plates inclined at 45 degrees. When this has been mastered so that uniform beads can be made consistently, practice on welding vertically may be started. Again begin with an easy operation such as running beads vertically on plates set at 45 degrees.
To progress with this practice it is necessary now to move the plates into vertical position. Welding vertically may be performed either by carrying the weld upward or starting from the top and welding down. It is generally conceded that working upward is easier and therefore, bead welds in this manner should be practiced. Since bead welds are of limited practical value, this experience must be extended by practicing on butt welds in the vertical and horizontal patterns.
In use, the beveled plate edges should be spaced on the backing strip and the strip tack welded to the plates on the reverse side.

Conclusion
It may be appreciated that no printed instruction can impart to the beginner the skill necessary for successful welding. Personal instruction by an experienced welding operator is the best means devised to date for accomplishing this end. Therefore, an effort should be made to secure some facility for instruction and practice under competent supervision. In any event the beginner should at least secure the benefit of criticism of finished welds by a qualified welder.

Abstract:

The arc welding segment of the industry seems to be growing the fastest with recent years showing maximum growth. The growth of the welding industry has been approximately 6% per year. Conventional electric arc welding equipment and filler metals represent over two-thirds of this total. Each segment of the industry and each welding process has its own growth patterns. In order to make a projection we must determine the past historic growth patterns, determine the present position, and consider those factors that will have an impact on the growth in the future.

Welding is now the universally accepted method of permanently joining all metals. In some respects, it might be considered a mature industry but it is still a growing industry. The true impact of welding on the metalworking industry should be measured in the value of the parts produced by welding, the amount of money saved by the use of welding over other metal fabrication processes, and in the value of products made possible by welding.
Historical data are available that record the growth of the welding equipment and materials industry, which in turn gives an indication of the projected growth for the future.
The arc welding segment of the industry seems to be growing the fastest with recent years showing maximum growth. The growth of the welding industry has been approximately 6% per year. Conventional electric arc welding equipment and filler metals represent over two-thirds of this total. Each segment of the industry and each welding process has its own growth patterns.
In order to make a projection we must determine the past historic growth patterns, determine the present position, and consider those factors that will have an impact on the growth in the future. Future growth of the arc welding processes depends on factors that may have an impact on the industries served by welding.
The future of these industries will largely determine the future of welding. It is possible to estimate the amount of each type of arc welding that is being done in the U.S.A. and how it is being applied. The most suitable approach for this analysis is to divide filler metals sold into the following categories:

• Covered electrodes (stick electrodes) all types
• Submerged arc welding electrode wire [solid steel larger than 1/16 in. (1.6mm) in diameter]
• Gas metal arc welding electrode wire [solid steel wire 1/16 in. (1.6mm) and smaller]
• Flux-cored arc welding electrode wire

At this point we can project into the future. This is done by charting the bar graph information into line charts and extending these lines for five years. This shows that based on the percentage of the total:

• Covered electrodes have been decreasing steadily for the last 14 years dropping from 81% to 59% and projected to 45%.
• Submerged arc welding has remained constant at about 5% to 7%.
• Gas metal arc welding has almost doubled, rising from 10% to 20%, and is projected to double again in the next ten years.
• Flux-cored welding is increasing, but at a slower rate.

This information shows that semiautomatic welding will greatly increase, machine and automatic welding will increase modestly, but manual welding is decreasing at least as a percentage of the total.
After analyzing recent trends in welding and manufacturing it becomes evident that the following must be considered with regard to the future of welding:

1. There will be continuing need to reduce manufacturing costs and to improve productivity, since (a) wage rates for the people in manufacturing industries will continue to increase, (b) the cost of metals for producing weldments and filler metals will also continue to be more expensive, and (c) energy and fuel costs will increase and shortages may occur.
2. There will be a continuing trend towards the use of higher-strength materials, particularly in the steels and lighter-weight materials.
3. There will be more use of welding by manufacturing industries, probably decreasing the use of castings.
4. There will be a trend towards higher levels of reliability and higher-quality requirements.
5. The trend towards automatic welding and automation in welding will accelerate.

Productivity is considered the amount of welding that can be done by a welder in a day. This is determined by several factors, the most important of which is the operator factor or duty cycle. Operator factor for a welder is the number of minutes per eight-hour period that is spent actually welding.
The different methods of welding have different average duty cycles. Manual welding has the lowest operator factor with semiautomatic welding approximately double and machine welding the next highest, with automatic welding approaching 100%. Efforts will be made to utilize those processes that have the highest-duty cycles. The expected trend will be away from manual welding towards semiautomatic welding and to machine or automatic welding when possible.
Another factor affecting productivity of welders relates to the deposition rate of the welding process. The higher current processes have the highest deposition rates, thus the submerged arc welding process and the electroslag welding process will remain important as costs must be reduced.
The next factor deals with increasing material costs. It is imperative to obtain the maximum utilization of filler metals. The cold wire type processes, gas tungsten arc and plasma arc, can actually deposit 100% of the filler metal purchased. Submerged arc welding, when the electrode only is considered, approaches 100% as does electroslag welding. Gas metal arc welding will give about 95% utilization. Flux-cored welding is the lowest of the continuous wire processes, normally in the 80% plus range. Covered electrodes have the lowest utilization because of the stub end and coating loss that results in approximately 65% of the weight of the filler metals purchased actually being deposited in the weld joint.
Another factor closely related to filler metal efficiency and operator factor is the total deposit of weld metal to produce a given weldment. If the amount of weld metal can be reduced to make a weld it is an economic savings, thus there is an advantage to methods such as narrow gap welding. The higher penetration characteristics of CO2 welding gives it an advantage over shielded metal arc welding because fillet weld sizes can be reduced and the same weld strength retained.
In forecasting the arc welding field, we will consider each process separately since each has its own historical development and utilization and will have a different future. However, the arc welding processes will continue to dominate the welding industry.
The shielded metal arc welding process is the oldest of the current arc welding processes but is losing ground in the total arc welding market. This trend will continue and manual electrode welding in the near future may represent only a third of arc welding.
The percentage of filler metal used by submerged arc welding has remained almost constant through the years. It is impossible to differentiate between filler metal used for electroslag welding and submerged arc welding; however, both processes will increase modestly.
Gas metal arc welding will continue to accelerate since it is being substituted for shielded metal arc, gas welding, brazing, and resistance welding. This process, since it is a continuous wire process with high filler metal utilization, will continue to rise at the highest rate.
The flux-cored arc welding process started from a lower base and has been gaining modestly. This trend will continue; however, lower filler metal utilization and higher filler metal cost will keep it from growing as fast as gas metal arc welding.
Gas tungsten arc welding will grow as fast or faster than the total welding market. There are three reasons; it is adaptable to automation, it is being used on high quality work, and for welding newer thin specialty metals.
Plasma arc welding will grow faster than gas tungsten arc as soon as its capabilities are better known.
Special automated fixtures will become increasingly important. It is expected that fixtures will soon be specified by the type of work and the size of work they are expected to perform, thus we will have automatic machines for seamers, for tank making, for pipe welding, for attaching spuds, for overlaying, and for other special applications. Automatic and computer-controlled machines will become more common place in the years ahead. Every effort will be made to reduce the amount of manual labor involved in making welds.
Some of the newer processes and some which are of a more specialized nature will grow quite rapidly; however, they will never become large segments of the total welding industry. These include electron beam welding, laser beam welding, friction welding, ultrasonic welding, diffusion welding, and cold welding.
With increased emphasis on welding as a basic manufacturing technology the growth rate in the future will approximate 8% per year and welding equipment shipments are expected to more than double in the next five years. Growth rate is expected to be shared by all of the different welding processes. However, the more conventional arc welding processes may not grow as fast as the more exotic processes primarily because of a larger base.