Rare Earth On Low Carbon Steel To Atmospheric Corrosion Can Affect Research

Rare Earth(RE) elements could improve the atmospheric corrosion resistance properties of steels, but the effective mechanism was not clear and there were not yet enough evidence to show how the RE to affect on the forming process and the structure of the rust layer,and what is the ultimate state of RE in the rust layer. In this paper, indoor accelerating corrosion test—alternate immersion corrosion test and salt spray test,and electrochemistry test were designed to investigate the role of RE on improving atmospheric corrosion resistance of steels and to research the mechanism why the addition of RE could improve atmospheric corrosion resistance of steels. The morphologies, composing and compactness of the rust layer have been observed and analyzed after different time of indoor accelerating corrosion test,the corrosion rate has been calculated after different time of indoor accelerating corrosion test,and the corrosion rate of tested steels at non-accelerating corrosion test has been tested and calculated to provide comparison and analysis.The research results have shown that: (1)In Cl- environment simulation condition, the addition of RE in steels could not evidently improve the corrosion resistance of mild steels, while the corrosion resistance of mild steel containing 0.12%RE was always better than that of mild steel without RE after different times fog corrosion test. On this condition, the rust layer of tested steels was very loose, less adhesive and non-protective. (2)In industrial environment simulation condition, the addition of RE could remarkably improve atmospheric corrosion resistance of mild steels, and the corrosion rate of mild steel containing 0.12%RE was 32% lower than that of mild steel without RE after 288 hours alternate immersion corrosion test. (3) In industrial environment simulation condition, RE promote the transition of the corrosion product from γ-FeOOH/γ-Fe₂O₃ to stable and protective a-FeOOH so that RE improved the adhesive and compactness of the rust layer.