Initiation and propagation of stress corrosion cracks for type 304L stainless steel in chloride solutions containing thiosulfate

The stress corrosion cracking (SCC) of Type 304L stainless steel in chloride solutions containing various concentrations of thiosulfate ions (S2O32-) has been studied by using a slow strain rate testing apparatus with a dynamic observation system. It was observed that intergranular cracks were initiated from pits and propagated with the evolution of bubbles. The SCC was found to occur >10(-3) M S2O32-, and the variation in the concentration of S2O32- from 10(-3) to 10(-1) M did not shown any marked difference in SCC susceptibility evaluated by maximum stress. According to the analysis of the cracking behavior from the observed images, crack propagation rate was found to increase slightly with increase in the concentration of S2O32-. The increase is considered to be caused by the change in the corrosion potential with the concentration. Apparent critical stress intensity factor for SCC was less scattered around 2-3 MNm(-3/2) and slightly increased with increase in the concentration. The strain where either a pit or a crack was initiated first and the number of pits and cracks decreased remarkably and increased with increase in the concentration, respectively. S2O32- mainly affects the initiation process of the pit and the crack more than the crack propagation process. (C) 1997 Elsevier Science Ltd.