A study on the repassivation kinetics and SCC behavior of duplex stainless steel in chloride solution

Abstract

Repassivation kinetics of duplex stainless steel (DSS) 2205 was examined using a scratched electrode technique in 4 M NaCl solution at 90 C with exploring the relation between the repassivation kinetics and the susceptibility to stress corrosion cracking (SCC) measured by slow strain rate test. The repassivation kinetics was analyzed by the relationship between the current density [i(t)] and the charge density [q(t)] that has flown from the scratch. During the repassivation, passive film nucleated according to the place exchange model and then grew according to the high-field ion conduction model in which log i(t) is linearly proportional to 1/q(t) with the slope, a parameter of repassivation kinetics. It was found that the lower the slope, the faster repassivated is the alloy, being hence higher resistance to SCC. The repassivation rate of DSS 2205 decreased with applied potential, as confirmed by the increase in the slope. With an increase in applied potential, the slope increased gradually, and reached a limiting value beyond which an inflection point appeared in the log i(t) vs 1/q(t) plot. Effects of applied potential on the failure mode of the alloy are well correlated with the change in the slope of the repassivation kinetics. (c) 2005 The Electrochemical Society.