Effect of silicon on the corrosion behaviour of 690 MPa weathering bridge steel in simulated industrial atmosphere

•The corrosion behaviour of 690 MPa bridge steel with different silicon contents was studied.•With increases in Si content, the corrosion rate of the test steel increases gradually, and the corrosion resistance decreases.•With increases in Si content, the protective index α/γ* of the rust layer decreases. The enrichment of Si in the rust layer leads to the failure of Cu, Cr and Ni enrichment to form a dense and continuous protective rust layer.•Si mainly exists in the form of Fe2SiO4, which is loose and porous and cannot prevent the entry of corrosive media such as O2 and HSO3-, and eventually leads to a low content of α-FeOOH phase. 690 MPa weathering bridge steel is a new generation of high strength bridge steel developed in China, and its corrosion resistance is the focus of attention. Wet/dry cyclic tests、electrochemical tests in conjunction with surface analysis techniques have been performed to study the role of silicon on the corrosion behaviour of 690 MPa weathering bridge steel in simulated industrial atmosphere. The results indicate that with the increase of Si content, the corrosion rate of the tested steel increases, the protection index α/γ* decreases, and the corrosion resistance decreases gradually. Si mainly exists in the rust layer in the form of Fe2SiO4, and the content of Fe2SiO4 in the rust layer depends on the Si content. The loose and porous Fe2SiO4 in the rust layer cannot prevent the entry of corrosive media such as O2 and HSO3-, would hinder the formation of the Fe3O4 phase, and eventually leads to a lower content of dense and stable α-FeOOH phase in the rust layer, which is very important for the rust layer protection. The above factors should be responsible for the poor corrosion resistance with high Si content.