(1) When metal-arc welding low carbon steels, the bare, thin coated or heavy coated shielded arc types of electrodes may be used. These electrodes are of low carbon type (0.10 to 0.14 percent).

(2) Low carbon sheet or plate materials that have been exposed to low temperatures should be preheated slightly to room temperature before welding.

(3) In welding sheet metal up to 1/8 in. (3.2 mm) in thickness, the plain square butt joint type of edge preparation may be used. When long seams are to be welded in these materials, the edges should be spaced to allow for shrinkage, because the deposited metal tends to pull the plates together. This shrinkage is less severe in arc welding than in gas welding, and spacing of approximately 1/8 in. (3.2 mm) will be sufficient.

(4) The backstep, or skip, welding technique should be used for short seams that are fixed in place. This will prevent warpage or distortion, and will minimize residual stresses.

(5) Heavy plates should be beveled to provide an included angle of up to 60 degrees, depending on the thickness. The parts should be tack welded in place at short intervals along the seam. The first, or root, bead should be made with an electrode small enough in diameter to obtain good penetration and fusion at the base of the joint. A 1/8 or 5/32 in. (3.2 or 4.0 mm) electrode is suitable for this purpose. The first bead should be thoroughly cleaned by chipping and wire brushing before additional layers of weld metal are deposited. Additional passes of the filler metal should be made with a 5/32 or 3/16 in. (4.0 or 4.8 mm) electrode. The passes should be made with a weaving motion for flat, horizontal, or vertical positions. When overhead welding, the best results are obtained by using string beads throughout the weld.

(6) When welding heavy sections that have been beveled from both sides, the weave beads should be deposited alternately on one side and then the other. This will reduce the amount of distortion in the welded structure. Each bead should be cleaned thoroughly to remove all scale, oxides, and slag before additional metal is deposited. The motion of the electrode should be controlled so as to make the bead uniform in thickness and to prevent undercutting and overlap at the edges of the weld. All slag and oxides must be removed from the surface of the completed weld to prevent rusting.

(1) The plates should be prepared for welding in a manner similar to that used for welding low carbon steels. When welding with low carbon steel electrodes, the welding heat should be carefully controlled to avoid overheating the weld metal and excessive penetration into the side walls of the joint. This control is accomplished by directing the electrode more toward the previously deposited filler metal adjacent to the side walls than toward the side walls directly. By using this procedure, the weld metal is caused to wash up against the side of the joint and fuse with it without deep or excessive penetration.

(2) High welding heats will cause large areas of the base metal in the fusion zone adjacent to the welds to become hard and brittle. The area of these hard zones in the base metal can be kept to a minimum by making the weld with a series of small string or weave beads, which will limit the heat input. Each bead or layer of weld metal will refine the grain in the weld immediately beneath it, and will anneal and lessen the hardness produced in the base metal by the previous bead.

(3) When possible, the finished joint should be heat treated after welding. Stress relieving is normally used when joining mild steel, and high carbon alloys should be annealed.

(4) In welding medium carbon steels with stainless steel electrodes, the metal should be deposited in string beads in order to prevent cracking of the weld metal in the fusion zone. When depositing weld metal in the upper layers of welds made on heavy sections, the weaving motion of the electrode should not exceed three electrode diameters.

(5) Each successive bead of weld should be chipped, brushed, and cleaned prior to the laying of another bead.

(1) The welding heat should be adjusted to provide good fusion at the side walls and root of the joint without excessive penetration. Control of the welding heat can be accomplished by depositing the weld metal in small string beads. Excessive puddling of the metal should be avoided, because this can cause carbon to be picked up from the base metal, which in turn will make the weld metal hard and brittle. Fusion between the filler metal and the side walls should be confined to a narrow zone. Use the surface fusion procedure prescribed for medium carbon steels (para 7-11).

(2) The same procedure for edge preparation, cleaning of the welds, and sequence of welding beads as prescribed for low and medium carbon steels also applies to high carbon steels.

(3) Small, high carbon steel parts are sometimes repaired by building up worn surfaces. When this is done, the piece should be annealed or softened by heating to a red heat and cooling slowly. The piece should then be welded or built up with medium carbon or high strength electrodes, and heat treated after welding to restore its original properties.

(1) Class I steels are used to make tools that work by a shearing or cutting actions, such as cutoff dies, shearing dies, blanking dies, and trimming dies.

(2) Class II steels are used to make tools that produce the desired shape of the part by causing the material being worked, either hot or cold, to flow under tension. This includes drawing dies, forming dies, reducing dies, forging dies, plastic molds, and die cast molding dies.

(3) Class III steels are used to make tools that act upon the material being worked by partially or wholly reforming it without changing the actual dimensions. This includes bending dies, folding dies, and twisting dies.

(4) Class IV steels are used to make dies that work under heavy pressure and that produce a flow of metal or other material caressing it into the desired form. This includes crimping dies, embossing dies, heading dies, extrusion dies, and staking dies.

(1) If the parts to be welded are small, they should be annealed or softened before welding. The edges should then be preheated up to 1000°F (538°C), depending on the carbon content and thickness of the plate. Welding should be done with either a mild steel or high strength electrode.

(2) High carbon electrodes should not be used for welding tool steels. The carbon picked up from the base metal by the filler metal will cause the weld to become glass hard, whereas the mild steel weld metal can absorb additional carbon without becoming excessively hard. The welded part should then be heat treated to restore its original properties.

(3) When welding with stainless steel electrodes, the edge of the plate should be preheated to prevent the formation of hard zones in the base metal. The weld metal should be deposited in small string beads to keep the heat input to a minimum. In general, the application procedure is the same as that required for medium and high carbon steels.

(1) Chromium alloy steels. Chromium is used as an alloying element in carbon steels to increase hardenability, corrosion resistance, and shock resistance, and gives high strength with little loss in ductility. Chromium in large amounts shortens the spark stream to one half that of the same steel without chromium, but does not affect the stream’s brightness.

(2) Nickel alloy steels. Nickel increases the toughness, strength, and ductility of steels, and lowers the hardening temperature so that an oil quench, rather than a water quench, is used for hardening. The nickel spark has a short, sharply defined dash of brilliant light just before the fork.

(3) High chromium-nickel alloy (stainless) steels. These high alloy steels cover a wide range of compositions. Their stainless, corrosion, and heat resistant properties vary with the alloy content, and are due to the formation of a very thin oxide film which forms on the surface of the metal. Sparks are straw colored near the grinding wheel, and white near the end of the streak. There is a medium volume of streaks which have a moderate number of forked bursts.

(4) Manganese alloy steels. Manganese is used in steel to produce greater toughness, wear resistance, easier hot rolling, and forging. An increase in manganese content decreases the weldability of steel. Steels containing manganese produce a spark similar to a carbon spark. A moderate increase in manganese increases the volume of the spark stream and the intensity of the bursts. A steel containing more than a normal amount of manganese will produce a spark similar to a high carbon steel with a lower manganese content.

(5) Molybdenum alloy steels. Molybdenum increases hardenability, which is the depth of hardening possible through heat treatment. The impact fatigue property of the steel is improved with up to 0.60 percent molybdenum. Above 0.60 percent molybdenum, the impact fatigue proper is impaired. Wear resistance is improved with molybdenum content above about 0.75 percent. Molybdenum is sometimes combined with chromium, tungsten, or vanadium to obtain desired properties. Steels containing this element produce a characteristic spark with a detached arrowhead similar to that of wrought iron, which can be seen even in fairly strong carbon bursts. Molybdenum alloy steels contain either nickel and/or chromium.

(6) Titanium and columbium (niobium) alloy steels. These elements are used as additional alloying agents in low carbon content, corrosion resistant steels. They support resistance to intergranular corrosion after the metal is subjected to high temperatures for a prolonged period of time.

(7) Tungsten alloy steels. Tungsten, as an alloying element in tool steel, tends to produce a fine, dense grain when used in relatively small quantities. When used in larger quantities, from 17 to 20 percent, and in combination with other alloys, tungsten produces a steel that retains its hardness at high temperatures. This element is usually used in combination with chromium or other alloying agents. In a spark test, tungsten will show a dull red color in the spark stream near the wheel. It also shortens the spark stream and decreases the size of or completely eliminates the carbon burst. A tungsten steel containing about 10 percent tungsten causes short, curved, orange spear points at the end of the carrier lines. Still lower tungsten content causes small, white bursts to appear at the end of the spear petit. Carrier lines may be from dull red to orange, depending on the other elements present, providing the tungsten content is not too high.

(8) Vanadium alloy steels. Vanadium is used to help control grain size. It tends to increase hardenability and causes marked secondary hardness, yet resists tempering. It is added to steel during manufacture to remove oxygen. Alloy steels containing vanadium produce sparks with detached arrowheads at the end of the carrier line similar to those produced by molybdenum steels.

(9) Silicon alloy steels. Silicon is added to steel to obtain greater hardenability and corrosion resistance. It is often used with manganese to obtain a strong, tough steel.

(10) High speed tool steels. These steels are usually special alloy compositions designed for cutting tools. The carbon content ranges from 0.70 to 0.80 percent. They are difficult to weld, except by the furnace induction method. A spark test will show a few long, forked spades which are red near the wheel, and straw colored near the end of the spark stream.

(1) Correct electrodes. Hydrogen is the number one enemy of sound welds in alloy steels; therefore, use only low hydrogen (MIL-E-18038 or MIL-E-22200/1) electrodes to prevent underbead cracking. Underbead cracking is caused by hydrogen picked up in the electrode coating, released into the arc, and absorbed by the molten metal.

(2) Moisture control of electrodes. If the electrodes are in an airtight container, place them, immediately upon opening the container, in a ventilated holding oven set at 250 to 300°F (121 to 149°C). In the event that the electrodes are not in an airtight container, put them in a ventilated baking oven and bake for 1-1/4 hours at 800°F (427°C). Baked electrodes should, while still warm, be placed in the holding oven until used. Electrodes must be kept dry to eliminate absorption of hydrogen. Testing for moisture should be in accordance with MIL-E-22200.

(1) General. It is important to avoid excessive heat concentration in order to allow the weld area to cool quickly. Either the heat input nomograph or the heat input calculator can be used to determine the heat input into the weld.

(2) Heat input nomograph. To use the heat input nomograph (fig. 7-9), find the volts value in column 1 and draw a line to the amps value in column 3. From the point where this line intersects colunm 2, draw another line to the in./min value in column 5. Read the heat units at the point where this second line intersects column 4. The heat units represent thousands of joules per inch. For example, at 20 volts and 300 amps, the line intersects column 2 at the value 6. At 12 in./min, the heat input is determined as 30 heat units, or 30,000 joules/in.

(3) Heat input calculator. The heat input calculator can be made by copying the pattern printed on the inside of the back cover of this manual onto plastic, light cardboard, or other suitable material and cutting out the pieces. If no suitable material is available, the calculator may be assembled by cutting the pattern out of the back cover. After the two pieces are cut out, a hole is punched in the center of each. They are then assembled using a paper fastener, or some similar device, which will allow the pieces to rotate. To determine welding heat input using the calculator, rotate until the value on the volts scale is aligned directly opposite the value on the speed (in./min) scale. The value on the amps scale will then be aligned directly opposite the calculated value for heat units. As with the nomograph, heat units represent thousands of joules per inch.

(4) Maximum heat input. Check the heat input value obtained from the nomograph or calculator against the suggested maximums in tables 7-17 and 7-18. If the calculated value is too high, adjust the amperes, travel speed, or preheat temperature until the calculated heat input is within the proper range. (The tables are applicable only to single-arc, shielded metal-arc, submerged arc, gas tungsten-arc, flux-cored arc, and gas metal-arc processes. They are not applicable to multiple-arc or electroslag welding, or other high heat input vertical-welding processes, since welds made by these in the "T-1" steels should be heat treated by quenching and tempering.) For welding conditions exceeding the range of the nomograph or calculator, the heat input can be calculated using the following formula:

(1) The most widely used type of cast iron is known as gray iron. Gray iron has a variety of compositions, but is usually such that it is primarily perlite with many graphite flakes dispersed throughout.

(2) There are also alloy cast irons which contain small amounts of chromium, nickel, molybdenum, copper, or other elements added to provide specific properties.

(3) Another alloy iron is 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.

(4) In white cast iron, almost all the carbon is in the combined form. This provides a cast iron with higher hardness, which is used for abrasion resistance.

(5) Malleable cast iron is made by giving white cast iron a special annealing heat treatment to change the structure of the carbon in the iron. The structure is changed to perlitic or ferritic, which increases its ductility.

(6) Nodular iron and ductile cast iron 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.

(7) Cast irons are widely used in agricultural equipment; on machine tools as bases, brackets, and covers; for pipe fittings and cast iron pipe; and for automobile engine blocks, heads, manifolds, and water preps. Cast iron is rarely used in structural work except for compression members. It is widely used in construction machinery for counterweights and in other applications for which weight is required.

(1) 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. The skin or high silicon surface should also be removed adjacent to the weld area on both the face and root side. The edges of a joint should be chipped out or ground to form a 60° angle or bevel. Where grooves are involved, a V groove from a 60-90° included angle should be used. The V should extend approximately 1/8 in. (3.2 mm) from the bottom of the crack. A small hole should be drilled at each end of the crack to keep it from spreading. Complete penetration welds should always be used, since a crack or defect not completely removed may quickly reappear under service conditions.

(2) Preheating is desirable for welding cast irons 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 cast iron. Preheat temperatures should be related to the welding process, the filler metal type, the mass, and the complexity of the casting. Preheating can be done by any of the normal methods. Torch heating is normally used for relatively small castings weighing 30.0 lb (13.6 kg) or less. Larger parts may be furnace preheated, and in some cases, temporary furnaces are built around the part rather than taking the part to a furnace. In this way, the parts can be maintained at a high interpass temperature in the temporary furnace during welding. Preheating should be general, since it helps to improve the ductility of the material and will spread shrinkage stresses over a large area to avoid critical stresses at any one point. Preheating tends to help soften the area adjacent to the weld; it assists in degassing the casting, and this in turn reduces the possibility of porosity of the deposited weld metal; and it increases welding speed.

(3) Slow cooling or post heating improves the machinability of the heat-affected zone in the cast iron adjacent to the weld. The post cooling should be as slow as possible. This can be done by covering the casting with insulating materials to keep the air or breezes from it.

(1) Electrodes.

(2) Arc Welding.

(3) Carbon-arc welding of cast iron. Iron castings may be welded with a carbon arc, a cast iron rod, and a cast iron welding flux. The joint should be preheated by moving the carbon electrodes along the surface. This prevents too-rapid cooling after welding. The molten puddle of metal can be worked with the carbon electrode so as to move any slag or oxides that are formed to the surface. Welds made with the carbon arc cool more slowly and are not as hard as those made with the metal arc and a cast iron electrode. The welds are machinable.

(4) Oxyfuel gas welding. The oxyfuel 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 and the copper zinc rods. Welds made with the proper cast iron electrode will be as strong as the base metal. Good color match is provided by all of these welding reds. 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: a manganese bronze and a low-fuming bronze. The deposited bronze has relatively high ductility but will not provide a color match.

(5) Brazing and braze welding.

(6) 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:

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 issued 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.

(7) 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. 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.

(8) Studding. Cracks in large castings are sometimes repaired by studding (fig. 7-10). In this process, the fracture is removed by grinding a V groove. Holes are drilled and tapped at an angle on each side of the groove, and studs are screwed into these holes for a distance equal to the diameter of the studs, with the upper ends projecting approximately 1/4 in. (6.4 mm) above the cast iron surface. The studs should be seal welded in place by one or two beads around each stud, and then tied together by weld metal beads. Welds should be made in short lengths, and each length peened while hot to prevent high stresses or cracking upon cooling. Each bead should be allowed to cool and be thoroughly cleaned before additional metal is deposited. If the studding method cannot be applied, the edges of the joint should be chipped out or machined with a round-nosed tool to form a U groove into which the weld metal should be deposited.

(9) Other welding processes can be used for cast iron. Thermit welding has been used for repairing certain types of cast iron machine tool parts. Soldering can be used for joining cast iron, and is sometimes used for repairing small defects in small castings. Flash welding can also be used for welding cast iron.

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