Effect of Cr‐For‐Cu Substitution on the Corrosion Behavior of 2 wt.% Ni Low‐Alloy Steel in Simulated Tropical Marine Atmosphere

The corrosion behavior and rust layer evolution of 2 wt.% Ni low‐alloy steel (2Ni LAS) with partial substitution of Cu by a small amount of Cr were investigated in a simulated tropical marine atmosphere. By integrating corrosion kinetics, rust layer morphology, phase composition, alloying element valence‐state evolution, and electrochemical response, the intrinsic effects of Cr‐for‐Cu substitution on the corrosion mechanism of 2Ni LAS were clarified. The results reveal that, compared to the original composition, replacing Cu with a small amount of Cr deteriorates the corrosion resistance of 2Ni LAS. This degradation originates from the altered selective enrichment and phase transformation in the rust layer. Specifically, Cr is preferentially found as non‐protective Cr(OH) 3 in the rust layer, accompanied by reduced Cu and Ni enrichment. Cu and Ni predominantly exist as fewer protective oxides or hydroxides, while the formation of beneficial phases such as CuFeO 2 and NiFe 2 O 4 is also suppressed. Consequently, the transformation of γ‐FeOOH and γ‐Fe 2 O 3 /Fe 3 O 4 into a stable α‐FeOOH phase is hindered, leading to a less compact and less protective rust structure. The degraded barrier properties facilitate the penetration and accumulation of Cl − at the matrix/rust interface, thereby promoting localized corrosion and accelerating the overall corrosion rate.