Corrosion behaviors at the initial stage of Q235 steel in Xisha atmosphere

The rust layer formed on the surface of Q235 steel subjected to a high temperature and high humidity marine atmosphere in Xisha Islands was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe micro analyzer (EPMA) and Raman Spectrum (RS). The results showed that corrosion behavior of Q235 steel was more severe in Xisha atmosphere than in other marine environments. The surface morphology was observed by SEM and the distributions of elements were analyzed by EPMA. There were many cracks and holes in the rust layer. Cl^- can penetrate into the rust-metal interface along the cracks and holes in the Q235 steel rust film. Outer rust of Q235 steel was mainly composed of β-FeOOH, γ-FeOOH and a little α-FeOOH. Much iron oxide, such as Fe₃O₄, γ-Fe₂O₃ were found in the inner of rust layer. These iron oxides could be deoxidized from FeOOH, and this can accelerate oxidation of substrate steel.