Microelectrochemistry on CrS and MnS Inclusions and Its Relation with Pitting Potentials of Stainless Steels

Abstract

The anodic dissolution behavior of CrS inclusions was compared with that of MnS inclusions containing around 10 at% Cr, (Mn,Cr)S, using a microelectrochemical cell in NaCl solutions. CrS inclusions were resistant to pit initiation compared with (Mn,Cr)S inclusions. The dissolution potential of CrS inclusions was found to be in the transpassive region of stainless steels. Stable pits were initiated in this potential region. (Mn,Cr)S inclusions dissolved in the passive region of stainless steels, providing lower pitting potentials than those of CrS-containing stainless steels. AES analysis of the surface films on CrS inclusions indicated that chromium-containing oxide films were formed on the CrS inclusions and grew with electrode potential, which suggested the oxide films on CrS inclusions prevented the anodic dissolution of the inclusions, thereby leading to an increased resistance to pit initiation.