Revealing the Effect of Ce on Pitting Corrosion Induced by Inclusions in Low Alloy Steel: Induction by CaS·C12A7 and Inhibition by CeAlO3.

Abstract

Low alloy steel faces localized corrosion issues in service environments, primarily due to pitting corrosion induced by inclusions. Conventional protective measures cannot significantly improve the corrosion resistance of the steel. In this study, an effective industrial approach was proposed to enhance the corrosion resistance of low alloy steels. Cerium (Ce) was added during the refining process to modify inclusions and alter the mechanism of inclusion-induced localized corrosion, thereby improving the substrate's ability to inhibit pitting corrosion. The effect of Ce treatment on the cleanliness of molten steel was investigated, and a kinetic model of inclusion evolution was established based on thermodynamic calculations. The pitting corrosion induced by CaS·C₁₂A₇ and CeAlO₃ inclusions was studied through immersion experiments over different durations. The degree of corrosion after being soaked for 20 min was significantly different. The size and depth of pitting pits induced by CeAlO₃ inclusions were much smaller than those induced by CaS·C₁₂A₇ inclusions. The electron back scatter diffraction tests confirmed that CaS·C₁₂A₇ inclusions exhibited a higher corrosion sensitivity compared to CeAlO₃, thus promoting the initiation of pitting. Electrochemical tests demonstrated a positive shift in the corrosion potential and a reduction in current density. This implies that CeAlO₃ inclusions can significantly inhibit pitting occurrences. Based on the dissolution behaviors of CaS·C₁₂A₇ and CeAlO₃ inclusions, a kinetic model was established to describe the initiation and propagation of pitting induced by these inclusions.