T.O. 33B-1-13-104k. WeldDefects. A variety of discontinuities may be formed during welding. Some are at the surface andsome are in the interior of the weldment. Some of the defects peculiar to weldments are lack ofpenetration, lack of fusion, undercutting, cracks in the weld metal, crater cracks, cracks in the heataffected zone, etc.3.7.4.1.3 SecondaryProcessingorFinishingDiscontinuities.In this group are those discontinuities associated with the various finishing operations after the part has been rough-formed by rolling, forging, casting or welding. Discontinuities may be introduced by machining, heat treating,grinding and similar processes. These are described below:a. MachiningTears. These are caused by dragging of the metal under the tool when it is not cuttingcleanly. Soft and ductile low carbon steels are more susceptible to this kind of damage than are theharder, higher carbon or alloy types. Machining tears are surface discontinuities and are readily foundwith magnetic particles.b. HeatingTreatingCracks. (See Figure 3-63.) When steels are heated and quenched to produce desiredproperties for strength or wear, cracking may occur if the operation is not correctly suited to thematerial and the shape of the part. Most common are quench cracks, caused when parts are heated tohigh temperatures and then suddenly cooled by immersing them in some cool medium, which may bewater, oil or even air. Such cracks often occur at locations where the part changes cross-section or atfillets or notches in the part. The edges of keyways and the roots of splines or threads are likely spotsfor quench cracks to occur. Cracks may also result from too rapid heating of the part, which may causeuneven expansion at changes of cross-section, or at corners where heat is absorbed more rapidly than inthe body of the piece. Corner cracking may also occur during quenching, because of more rapid heatloss at such locations. Heat treating cycles can be designed to minimize or eliminate such cracking, butfor critical parts, testing with magnetic particles is a safety measure usually applied, since such cracksare serious and their detection presents no difficulty.Figure 3-63. Magnetic Particle Indications of Quenching Cracks Shown with Dry Powder.
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