Effect of applied stress on dissolution morphology and pit initiation behavior of MnS inclusion in stainless steel

Microelectrochemical measurements were carried out to ascertain the effect of stress on the dissolution morphology and pit initiation behavior of (Mn,Cr)S inclusions, which contained around 15 at. % chromium. Under anodic polarization, the selective dissolution of MnS and the composition change from the (Mn,Cr)S to CrS occurred in 1.5 mol kg^-1 MgCl₂. No stable pit was initiated under no applied stress, even though the MnS dissolution and the formation of meta-stable pits were observed. Under applied stress, a stable pit was initiated in the potential range of the MnS dissolution, and small cracks that were perpendicular to a tensile direction were generated. The cracks were thought to be induced by a mechano-chemical reaction, and propagated to the steel under the inclusion. The steel matrix was then exposed to the solutions, and stable pitting was initiated at the inclusions under applied stress.