The mechanism of intergranular stress corrosion cracking of sensitised austenitic stainless steel in dilute thiosulphate solution

Corrosion current pulses associated with the nucleation of microcracks and their movement across single grain boundary facets were detected for intergranular stress corrosion cracking (IGSCC) of sensitised type 304 stainless steel induced by dilute thiosulphate solutions at ambient temperature. Estimates of crack-tip dissolution width and current density were derived. Cracks initiated as a consequence of non-uniform deformation around grain boundaries, and most stopped after penetration of at most a few grain-boundary facets. The idea of microstructural barriers to the propagation of short stress corrosion cracks was developed; such barriers became less important as the chemistry of the environment became more aggressive; a simple statistical model, based on a jump probability to cross a barrier, was developed for crack advance, and in part for the statistics of failure by IGSCC. At higher strain, fatal cracks initiated from a pre-existing microcrack. Strain-induced martensite formation resulted in a decrease with increasing strain in both microcrack nucleation frequency and penetration. © 1991.