Essential role of element Si in corrosion resistance of a bridge steel in chloride atmosphere

The role of element Si in corrosion of a bridge steel was investigated in chloride atmosphere. The effect of Si addition on steel corrosion depends on the Si content and testing time. For Si-containing steels, the corrosion resistance is enhanced due to formation of SiO2 with a network structure, facilitating α-FeOOH formation, the reduction of the anion selectivity and enrichment of Cu and Cr in the inner rust layer. However, after long-term testing, for 0.32Si and 0.40Si steels, the unstable silicon-oxytetrahedron compound with Q1 bond is formed, making the rust layer loose and porous, the corrosion resistance of steels reduces.