Corrosion resistance of rare earth (La, Ce) microalloyed stainless steel

The rare earth microalloying technique provides a key approach to enhance the corrosion resistance of stainless steel, serving as a modified inclusion to optimize steel properties This study systematically evaluated the effect of rare earth microalloying on the corrosion resistance of 304 austenitic stainless steel in a 3.5 wt.% NaCl solution, utilizing characterization techniques such as SEM and XPS. Rare earth doping effectively modified the composition of inclusions, optimized the density of the passivation film, which synergistically enhanced the corrosion resistance of the stainless steel. The results indicate that rare earth microalloying transforms harmful inclusions (e.g., Mn-S and Al-O) into more stable rare earth-based inclusions, effectively reducing manganese-rich phases and enhancing microstructural stability. This transformation process is validated by negative Gibbs free energy values, eliminating preferred corrosion initiation sites and thereby strengthening corrosion resistance. Furthermore, electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests reveal significantly enhanced passivation film resistance (Rp) in rare-earth microalloyed steels, and the samples exhibit n-type semiconductor characteristics with substantially reduced defect and carrier densities. Combined XPS analysis indicates that rare-earth microalloying promotes the formation of chemically uniform, dense passivation films rich in Cr and Fe oxides. By investigating the synergistic effects of rare earth elements on inclusions and passivation films, this study elucidates the mechanism by which rare earth microalloying significantly enhances the overall corrosion resistance of alloys in severe chloride environments. This research provides a reliable pathway for designing advanced stainless steels with superior resistance to chloride-induced degradation.