Cu-Mn weathering steel shows excellent atmospheric corrosion resistance in both coastal and industrial environments, which demonstrates that Cu and Mn have a synergistic effect on improving the corrosion resistance of steel. In the present paper, several experimental methods were used to research the synergistic effect at the aspects of structure, composition, the distribution and chemical state of alloying elements and the ion selectivity of rust layer.
In simulated coastal environment, the corrosion resistance of Cu-Mn weathering steel is better than that of Q235 mild steel. The synergistic effect of Cu and Mn is listed as follows: (1) On improving the structure of rust layer, addition of Cu and Mn can reduce cracks and pores in rust layer; (2) On altering the composition of rust, it can increase the amount of Fe3O4 and γ-FeOOH, while decrease that of β-FeOOH; (3) On the chemical state of alloying elements and selectivity of rust layer, it mainly convert the anion selectivity to canoed selectivity; (4) On the electrochemical aspect, it can decrease the anode current density and increase the corrosion potential of steel. Due to the reasons mentioned above, Cu-Mn weathering steel shows excellent atmospheric corrosion resistance in simulated coastal environment.
In simulated industrial environment, the corrosion resistance of Cu-Mn weathering steel is also better than that of Q235 mild steel. There are a few differences on the synergistic effect of Cu and Mn compared to in simulated coastal environment: (1) It is the same on improving the structure of rust layer and the chemical state of alloying elements and selectivity of rust layer; (2) On altering the composition of rust, it can increase the amount of γ-FeOOH, while decrease that of Fe3O4; (3) On the electrochemical aspect, it can accelerate the cathode deoxidize and restrain anode dissolution, and increase the corrosion potential of steel. These differences may be caused by the different influence of Cl- and HSO3- ions.
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