Influence of surface oxide layer formed during hot rolling on the atmospheric corrosion resistance of 720 weathering steel

Weathering steel has potential use in solar photovoltaic brackets owing to its satisfactory atmospheric corrosion resistance and good mechanical properties. In this study, an exposure experiment was conducted in an industrial atmospheric environment. The corrosion weight gain, macro-morphology, micro-morphology, X-ray diffraction (XRD), Raman, and electrochemical characteristics of a new 720 weathering steel with and without a surface oxide layer and Q235 with a surface oxide layer formed during hot rolling were compared. The corrosion characteristics were identified, and the underlying mechanism of the effect of the surface oxide layer formed during hot rolling on corrosion resistance was analyzed. The experimental and analytical results show that the rusting coat on Q235O and WS is relatively loose with cracks, and the main component is γ-FeOOH, while the rust of WSO is dense, and stable α-FeOOH formed in the inner rust layer after exposure for 8 months. The Cu element is enriched in the rust layer, which hinders the diffusion of corrosive Cl ions into the substrate. The surface oxide layer formed during hot rolling accelerates the formation of a stabilized rust layer in weathering steel and significantly reduces its corrosion rate of weathering steel in atmospheric corrosion.