Predicting SCC susceptibility of austenitic stainless steel by rapid scratching electrode technique

Abstract

The repassivation kinetics of rapidly scratched scars on surfaces of austenitic stainless steel in a chloride solution was examined using an ampero-chronometric method, and their relationship to SCC susceptibility measured by slow strain rate tests (SSRT) was explored. Repassivation kinetics was analyzed in terms of the current density flowing from the scratch, i(t), as function of the charge density that has flowed from the scratch, q(t). The log i(t) has a linear relationship with 1/q(t) in which the slope determined from the linear relationship was found to be very effective as a measure of repassivation rate. The alloy/environment system with a lower value of the slope showed the faster repassivation rate and also caused the thinner and more protective passive film to be formed during the repassivation. With an increase in applied potential, the slope increased gradually and reached asymptotically a limiting value beyond which an inflection point appeared in the log i(t) vs. 1/q(t) plots. The change in the slope with applied potential was correlated with the SCC susceptibility. Based on this correlation, a new method is proposed for the prediction of SCC susceptibility in terms of repassivation kinetics.