(A) study on the relationship between repassivation kinetics and stress corrosion cracking of austenitic stainless steels

Abstract

Repassivation kinetics of rapidly scratched scars on surfaces of type 304, 316 austenitic stainless steels in chloride environments were examined by ampero-chronometric method, and their relationship to SCC susceptibility, measured by constant extension rate tests and constant load tests, were explored. Effects of applied potential, solution temperature, chloride ion concentration and applied stress was analysed. On the basis of experimental results, a new quantitative criterion is proposed for the prediction of susceptibility to stress corrosion cracking. This is apparent activation barrier for repassivation, physical meaning of which is the degree of instability of newly growing film. With an increase in applied potential, solution temperature, and chloride ion concentration, apparent activation barrier for repassivation increased approaching asymptotically to a limiting value, and thereafter metal dissolution reaction was dominant over the repassivation process. Increase in activation barrier for repassivtion increased the susceptibility to stress corrosion cracking and as reached to a limiting value, SCC occurred under stressed condition. As metal dissolution reaction was dominant, tensile specimens were failed by general corrosion rather than stress corrosion cracking.