Stress Corrosion Cracking Susceptibility of AISI 316 NG and 316 Stainless Steel in an Impurity Environment

The relative stress corrosion cracking (SCC) susceptibility of heat-treated AISI 316 nuclear grade (NG) and 316 stainless steel (SS) has been investigated by means of constant extension rate tensile (CERT) tests over a range of strain rates from 10−5 to 10−7 s−1 in simulated boiling water reactor (BWR) environments that contain SO42− as an impurity. It is observed that although AISI 316 NG SS is extremely resistant to intergranular SCC (IGSCC) even when subjected to severe heat treatments, it can become susceptible to transgranular SCC (TGSCC) in the presence of impurities. Sensitized AISI 316 SS, however, is susceptible to IGSCC even in high-purity water containing 0.2 ppm O2, and the addition of an impurity aggravates the IGSCC susceptibility. The SCC results obtained for both materials are discussed in terms of a phenomenological model that incorporates a slip-dissolution mechanism and elastic-plastic fracture mechanics. The results for both IGSCC and TGSCC are demonstrated to be consistent with the slip-dissolution model of Ford.