Differences in Corrosion Behavior of Ferritic and Austenitic Stainless Steels

Effects of chromium (Cr) and molybdenum (Mo) on differences in corrosion behavior of ferritic and austenitic stainless steels (SS) were investigated to clarify the reason for the superior corrosion resistance of high-alloy ferritic SS to austenitic SS. In the region where the corrosion index (Cr + 3×Mo [mass%]) exceeded 32 to 35, ferritic SS showed superior pitting and crevice corrosion resistance to austenitic SS. Cr produced different effects on the anodic polarization behavior of ferritic and austenitic SS in solutions with low pH and high concentrations of chloride. The superiority of high-alloy ferritic SS could be explained by this behavior.