Experimental and DFT-based computational study on corrosion behavior of micro-alloyed steel in 3.5% NaCl solution

This study investigates the corrosion behavior of API-grade steels micro-alloyed with Cr, Mo, and V in a 3.5 wt.% NaCl solution through a combined experimental and theoretical approach. Electrochemical techniques, weight loss evaluations, and surface analyses were complemented by density functional theory (DFT) calculations to elucidate initial adsorption and oxidation mechanisms. Cr additions significantly enhanced corrosion resistance by promoting the formation of compact and protective oxide layers such as α-(Fe, Cr)OOH and FexCr3-xO4 (1 ≤ x ≤ 1.5). Co-addition of V increased initial surface reactivity through strong oxygen adsorption and charge transfer, facilitating early-stage oxidation, followed by a reduction in subsequent anodic dissolution due to elevated Fe escape energy. V suppressed coarse M7C3 carbide formation by favoring fine V-carbide precipitates, which may retain more Cr in solid solution. Mo addition, even in small quantities, further improved corrosion resistance by enhancing water adsorption and stabilizing surface oxides with minimal charge transfer. However, excessive carbide formation in steels with higher Cr and slightly elevated C markedly reduced corrosion resistance, which was effectively mitigated by water quenching. The quenched sample exhibited the most uniform corrosion scale and the highest resistance. These findings provide practical insight into alloying and thermal processing strategies for enhancing corrosion resistance in marine environments.