Grain ultra-refinement–induced multilayer co-enrichment of Cr and Si in the rust layer enhances corrosion resistance of weathering steel

Abstract In this work, the formation and evolution of the rust layer on coarse-grained (25.0 µm) and ultrafine-grained (0.5 µm) weathering steels were investigated through wet/dry cyclic corrosion test in 3.5 wt% NaCl solution, aiming to elucidate the synergistic effect of alloying elements Cr and Si on the corrosion resistance of weathering steel. Grain ultra-refinement enhances the electrochemical activity of weathering steel, leading to the co-enrichment of alloying elements Cr and Si within the rust layer in the form of a multilayered structure. The enrichment of Cr and Si within the rust layer results in the formation of multilayered Cr3+ and Si2+ compound oxides, which serve as an effective barrier against the permeation of corrosive media. In addition, the enrichment of alloying elements Cr within the rust layer facilitates the transformation of rust constituents into fine-grained α-FeOOH, contributing to the development of a stable, compact, and protective rust layer. Consequently, the rust layer formed on ultrafine-grained weathering steels exhibits excellent compactness and protectiveness, which enhances corrosion resistance and inhibits localized corrosion.