a. General. High yield strength, low alloy structural steels (constructional alloy steels) are special steels that are tempered to obtain extreme toughness and durability. The special alloys and general makeup of these steels require special treatment to obtain satisfactory weldments. These steels are special, low-carbon steels containing specific, small amounts of alloying elements. They are quenched and tempered to obtain a yield strength of 90,000 to 100,000 psi (620,550 to 689,500 kPa) and a tensile strength of 100,000 to 140,000 psi (689,500 to 965,300 kPa), depending upon size and shape. Structural members fabricated from these high strength steels may have smaller cross-sectional areas than common structural steels and still have equal strength. These steels are also more corrosion and abrasion resistant than other steels. In a spark test, these alloys produce a spark very similar to low carbon steels.b. Welding Technique. Reliable welding of high yield strength, low alloy structural steels can be performed by using the following guidelines:
To prevent underbead cracking, only low hydrogen electrodes should be used when welding high yield strength, low alloy structural steels.
Moisture stabilizer is an ideal holding oven for field use.
c. Low Hydrogen Electrode Selection. Electrodes are identified by classification numbers which are always marked on the electrode containers. For low hydrogen coatings, the last two numbers of the classification should be 15, 16, or 18. Electrodes of 5/32 and 1/8 in. (4.0 and 3.2 mm) in diameter are the most commonly used, since they are more adaptable to all types of welding of this type steel. Table 7-14 lists electrodes used to weld high yield strength, low alloy structural steels. Table 7-15 is a list of electrodes currently established in the Army supply system.
d. Selecting Wire-Flux and Wire-Gas Combinations. Wire electrodes for submerged arc and gas-shielded arc welding are not classified according to strength. Welding wire and wire-flux combinations used for steels to be stress relieved should contain no more than 0.05 recent vanadium. Weld metal with more than 0.05 percent vanadium may brittle if stress relieved. When using either the submerged arc or gas metal-arc welding processes to weld high yield strength, low alloy structural steels to lower strength steels the wire-flux and wire-gas combination should be the same as that recommended for the lower strength steels.
e. Preheating. For welding plates under 1.0 in. (25.4 mm) thick, above 50°F (10°C) is not required except to remove surface moisture metal. Table 7-16 contains suggested preheating temperatures.