MECHANISM OF CHLORIDE STRESS CORROSION CRACKING OF AUSTENITIC STAINLESS STEELS

Electrochemical studies were made in aqueous LiCl, MgCl//2, and MgBr//2 solutions and in ZnCl//2/KCl molten salt to clarify the corrosion reactions related to stress corrosion cracking (SCC) of austenitic stainless steel and to better define environmental variables critical to the occurrence of chloride SCC. SCC was observed in concentrated MgBr//2 solutions. H//2O must be present in the electrolyte, as SCC did not occur in dry molten ZnCl//2/KCl and H//2 evolution from corroding specimens may be facilitated by anodic polarization. A model of SCC requiring hydrogen evolution at the crack tip isproposed, with emphasis being placed on the effect of anodic reactions within the crack maintanining high acidity near the crack tip.