<p>This study systematically investigated the effects of variations in Zr and Mn content on the corrosion resistance of ferritic/martensitic (F/M) steel in a 3.5 wt.% NaCl solution. The results demonstrate a non-monotonic dependence of corrosion resistance on alloying content, with initial enhancement followed by degradation as Zr and Mn contents increased. The optimal corrosion resistance was achieved at Zr and Mn contents of 0.17 and 1.2 wt.%, respectively. Zr enhanced corrosion resistance by reducing M₂₃C₆ carbides precipitation and coarsening martensitic laths, whereas excessive Zr led to coarse Zr(C, N) particle formation, deteriorating corrosion performance. Similarly, Mn improved corrosion resistance through passive film stabilization at optimal contents (1.2 wt.%), but excess Mn refined the martensitic lath structure, reducing corrosion resistance properties. These findings provide critical insights for alloy design, establishing quantitative composition thresholds that balance microstructural and electrochemical factors to maximize corrosion resistance in chloride environments.</p>