Effect of Ni Addition on Corrosion Behavior of Weathering Steels Under Rust Layers in a Wet-Dry Cyclic Environment Containing Chloride Ions

摘要

Weathering steels are low alloy steels containing Cu, Ni, and Cr. Weathering steels form dense and adherent corrosion products during a long-term exposure to the outdoor environments. The protective rusts inhibit the diffusion of corrosive species such as chloride ions and oxygen to steel surfaces, resulting in reduction of the corrosion rate. However, it is well known that the protective rusts are not formed in the environments with a high chloride concentration, and weathering steels are not available in coastal areas. It is reported that Ni as an alloying element is effective to reduce the corrosion rate of weathering steels in chloride-containing environments. Although many researches showed that the protectiveness of rust layers was improved by the Ni addition to weathering steels, its detailed mechanism has not been clarified. In this study, we focused on the corrosion behavior of the weathering steels under rust layers. We investigated the corrosion resistance and the corrosion morphology of Ni-added weathering steel, conventional weathering steel, and carbon steel in a wet-dry cyclic environment containing chloride ions, and discussed the effect of Ni addition on the improvement of the corrosion resistance of weathering steels.