Prediction of the Stress Corrosion Cracking Susceptibility of Type 304 Stainless Steel in Terms of Repassivation Kinetics

The repassivation kinetics of rapidly scratched scars on surfaces of 304 austenitic stainless steel in chloride environments was examined using an ampero-chronometric method, and their relationship to stress corrosion cracking(SCC) susceptibility measured by slow strain rate tests(SSRT) was explored. Repassivation kinetics were analyzed in terms of the current density flowing from the scratch, i(t), as a function of the charge density that has flowed from the scratch, q(t). The slope determined from the log i(t) vs. 1/q(t) plots was found to be very effective as a measure of repassivation kinetics. The lower the slope, the more stable is the passive film formed during 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