Passivity of (Mn,Cr)S inclusions in type 304 stainless steel: The role of Cr and the critical concentration for preventing inclusion dissolution in NaCl solution
Masashi Nishimoto, Izumi Muto, Yu Sugawara, Nobuyoshi Hara
Abstract
The quantitative effects of the Cr concentration in (Mn,Cr)S inclusions in stainless steel on the dissolution and surface oxide properties of inclusions were investigated by microscale polarization and Auger electron spectroscopy. The onset potential of inclusion dissolution increased with the Cr concentration and reached the transpassive region of stainless steel when the Cr/(Mn + Cr) ratio of the inclusions was greater than 0.5. The surface oxide layer on Cr-rich inclusions was thicker and more Cr-enriched than on Mn-rich inclusions. Increasing the Cr concentration improved the protective ability of the oxide layer, resulting in the prevention of inclusion dissolution and higher pitting potentials.