Stress Corrosion Cracking Of High Strength Stainless Steels In Atmospheric Environments

High-strength steels are susceptible to delayed cracking under suitable conditions. Frequently such a brittle failure occurs at a stress that is only a fraction of the nominal yield strength. Considerable controversy exists over whether such failures result from two separate and distinct phenomena or whether there is but one mechanism called by two different names. Stress-corrosion cracking is the process in which a crack propagates, at least partially, by the stress induced corrosion of a susceptible metal at the advancing tip of the stress-corrosion crack. There is considerable evidence that this cracking results from the electrtrochemical corrosion of a metal subjected to tensile stresses, either residual or externally applied. Hydrogen-stress cracking is cracking which occurs as the result of hydrogen in the metal lattice in combination with tensile stresses. Hydrogen-stress cracking cannot occur if hydrogen is prevented from entering the steel, or if hydrogen that has entered during processing or service is removed before permanent damage has occurred. It is generally agreed that corrosion plays no part in the actual fracture mechanism. This report was prepared to point out wherein the two fracture mechanisms under consideration are similar and wherein they differ. From the evidence available today, the present authors have concluded that there are two distinct mechansims of delayed failure. (Author).

The susceptibility of six stainless steels to stress corrosion has been determined by exposing self-stressed specimens indoors and outdoors at ambient temperatures and also at 550 F (56l K). The salt-coated stainless steels were resistant to stress corrosion cracking at 550 F (56l K) for exposures from 4000 to 10,000 hours. Specimens of AM-350 DA and AM-367 stainless steel were found to be very susceptible to stress-corrosion cracking with exposures less than 5000 hours in both the indoor (with a salt coating) and outdoor (with and without a salt coating) environments, while the AM-350 CRT, AISI 501, PH l5-7 Mo, and PH 14-8 Mo displayed excellent resistance. In general, the stainless steels with higher austenite contents appeared to have better resistance to the corrosive effects of salt, both at rooni temperature and at 550 F (56l K).

Details the many conditions under which stress-corrosion cracking (SCC) can occur, the parameters which control SCC, and the methodologies for mitigating and testing for SCC, plus information on mechanisms of SCC with experimental data on a variety of materials. Contains information about environmen