Manganese effects on repassivation kinetics and SCC susceptibility of high mn-n austenitic stainless steel alloys

Abstract

Effects of Mn on the localized corrosion, repassivation kinetics, and stress corrosion cracking (SCC) of high Mn-N stainless steels (SSs) were examined in chloride solutions and compared with those of type 304 SS. The resistance to pitting corrosion of high Mn-N SSs decreased with an increase in Mn content at the expense of Ni. Repassivation kinetics of the high Mn-N SSs was analyzed by the relationship between the current density i(t) and the charge density q(t) that has flown from the scratch; passive film initially nucleated according to the place exchange model and then grew according to the high-field ion conduction model in which log i (t) vs 1/q(t) has a linear relationship with a slope (cBV). The repassivation rate of the alloys, analyzed by the (cBV) value, was decreased with an increase in the Mn content. The resistance to SCC of the alloys measured in 25% MgCl2 was in good agreement with that predicted, based on their repassivation rate. The deleterious effects of Mn on the localized and stress corrosion of the alloys appear to be associated with an increase in number and size of nonmetallic inclusions such as (Mn, Cr) oxides with Mn content. (c) 2007 The Electrochemical Society.