Grinding-induced degradation in the pitting corrosion resistance of stainless steel: insights into passive film and MnS

Abstract

This study investigates the effect of surface grinding on the pitting corrosion resistance of high-S and low-S Type 304 stainless steels. Microelectrochemical analysis reveals that MnS inclusions serve as the initiation sites for pitting, whereas no pitting occurs in MnS-free regions. Severe grinding with #60 SiC paper significantly reduces the pitting potential, whereas moderate grinding with #320 SiC paper produces only a negligible change. The reduction in pitting corrosion resistance is attributed to grinding-induced alterations in MnS morphology, including deformation and embedding. In contrast, moderate grinding (#320 SiC paper) does not significantly alter MnS morphology and therefore preserves pitting corrosion resistance comparable to that of mirror-polishing surfaces. Grinding introduced unevenness of passive film thickness, and the intersections between MnS inclusions and scratches act as preferential pit initiation sites. However, the decrease in protective capability of the passive films alone does not fully account for the observed decrease in pitting potential following severe grinding.