STRUCTURAL CHANGES IN HIGH-STRENGTH STEEL ASSOCIATED WITH STRESS CORROSION AND ITS RELATIONSHIP TO DELAYED FAILURE.
Summary rept., 29 Jun 64-29 Jun 65,
BATTELLE MEMORIAL INST COLUMBUS OH
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Studies of the structural changes associated with stress corrosion and delayed failure in AISI 4340 steel have shown that significant changes take place in both the internal structure and the fracture-sufrace morphology as a result of specific treatments, particularly the cathodic portion of the corrosion reaction. The incipient stage of stress cracking may be the result of stress corrosion, hydrogen embrittlement, or both, inasmuch as either corrosion or cathodic charging regenerates visible stacking faults in martensite. The regeneration of these stacking faults is believed to be the cause of transgranular fracture in the initial stages of stress-corrosion cracking. Examination of the fracture-surface morphology of stress-corrosion cracked and hydrogen-cracked alloys indicates that, after the initial reaction, hydrogen diffuses to and along prior-austenite grain boundaries and causes intergranular failure. The most likely mechanism for intergranular failure appears to be reduction of prior-austenite grain boundary energy as a result of adsorbed hydrogen. The analysis of fracture morphology of stress-corrosion failures is compared with that of a hydrogen-cracked fracture surface modified by a subsequent anodic treatment in the corrosion medium. Author