Corrosion Micro- and Macro-electrochemical Behavior of Rusted Carbon Steel and Weathering Steel

Scanning electrochemistry microscope(SECM) was used to investigate corrosion behavior of carbon steel and weathering steel under wet/dry cycle conditions, combined with polarization curves, electrochemical impedance spectroscopy(EIS), scanning electron microscopy(SEM) and X-ray diffraction(XRD). The corrosion process of rusted carbon steel and weathering steel are subjected to the anodic dissolution of Fe, and the existence of rust layer promotes the reduction of oxygen. Both macro-electrochemical and SECM test show that in the experimental period, the formation of the rust layer in the initial stage reduces the anodic dissolution rate, thereby improves the corrosion resistance of carbon steel and weathering steel, while the rust layer formation in the later period of the experimental results in the increase of corrosion rate due to the changes of its composition and structural characteristics. The corrosion rate of weathering steel and the oxygen reduction rate are higher than that of carbon steel, which are conducive to the formation of rust layer, thus contributing to long-term protection of steel, but the rust layer of weathering steel does not have very good protection in the short term. Rust layer is relatively loose, porous and not dense enough, and the main composition of rust layer is crystalline gamma-FeOOH, Fe3O4 and gamma-Fe2O3.