Correlation Between Nonmetallic Inclusions and Localized Corrosion of a Low‐Nickel Stainless Steel with Cerium Treatment

Abstract

The localized corrosion induced by different kinds of inclusions in low‐nickel stainless steel is studied through immersion tests and first‐principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce‐O‐S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium‐containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium‐containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS > Si‐Mn(‐Al)‐O > MnS > Ce‐C‐O‐S > Ce‐Si‐Mn(‐Al)‐O > Ce‐O‐S. For cerium‐containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium‐containing inclusions is cerium oxides > cerium sulfides > cerium oxysulfide.