Mechanical criterion for nucleation of intergranular stress corrosion cracking in austenitic stainless steel

This study investigated mechanical criteria for the nucleation of intergranular stress corrosion cracking (IGSCC) in thermally-sensitized type 304 austenitic stainless steel. Constant load testing was conducted on a stainless steel specimen in a tetrathionate solution, and the cracking behavior, including crack initiation, coalescence, and growth at grain boundaries (GBs) on the specimen surface, was observed in situ . Local normal strains along GBs were measured on the smooth surface via the digital image correlation (DIC) technique. Local normal stresses at GBs were estimated using the Schmid-modified grain boundary stress (SMGBS) model, which has been widely used for evaluating the stress state of GBs, considering the effect of the GB plane geometry and grain orientations of grains adjacent to the GBs. The relationship between IGSCC nucleation sites, strains, and stresses was discussed. As a result, there was a slight correlation between local normal stress obtained via the SMGBS model and local normal strain via DIC measurement. The use of experimentally measured local normal strain was found to be suitable to characterize IGSCC nucleation sites.