Intergranular stress-corrosion cracking (IGSCC) of austenitic stainless steels and nickelbase alloys continues to be a major problem in light water reactors. Although most research has been done on the mechanism of IGSCC, little is known about the process of crack
nucleation in these alloys. Scanning probe microscopy (SPM) was used to demonstrate that upon plastic deformation of annealed and sensitized Type 304 stainless steel specimens, slip intensifies at the grain boundaries, which results in grain boundary separation, particularly at
grain boundary triple points. Initial work has been conducted with in-situ atomic force microscopy (AFM) in an aqueous 1000 ppm sodium thiosulfate solution, to demonstrate that the observed grain boundary separations setve as stress-corrosion crack nucleation sites.