Electrochemical and Compositional Insights into Early-Stage Corrosion Behavior of High-Mn Steel Microalloyed with Cr, Mo, and V in 3.5% NaCl Solution

Abstract

Early-stage corrosion product formation governs the long-term performance of high-Mn steels in chloride environments, yet quantitative insights into this critical stage remain limited. To elucidate the individual and synergistic effects of Cr, Mo, and V, two alloys, MoV and CrMoV, were immersed in 3.5 wt% NaCl solution and analyzed during early immersion. Electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) revealed that CrMoV achieved a peak polarization resistance of 2897 Ω cm² at 12 h, which was 72% higher than that of MoV (1685 Ω cm² at 6 h), while reducing the corrosion current density from 1.35 to 0.45 µA cm⁻². Mott-Schottky analysis further indicated a 21% decline in defect density (from 7.2 × 10¹⁷ to 5.8 × 10¹⁷ cm⁻³ over 24 h), along with the emergence of mixed p-type and n-type semiconducting behavior. Cr-induced pseudo-passivation in the CrMoV alloy was primarily responsible for enhancing corrosion resistance and reducing metal dissolution, resulting in a thinner oxide layer than in MoV, as confirmed by FE-SEM and GDS analyses. XPS depth profiling revealed increasing Cr₂O₃ content over time and the formation of FeCr₂O₄ in the inner oxide layer by 12 h. Mo primarily reduced defect density, while V contributed to film thickening and uniformity. These synergistic effects improved early-stage corrosion resistance by up to 65%, offering practical guidance for designing corrosion-resistant high-Mn steels in marine applications.