Effect of Ca and S on the Simulated Seaside Corrosion Resistance of 1.0Ni-0.4Cu-Ca-S Steel

Atmospheric corrosion resistance of 1.0Ni-0.4Cu-Ca-S steels was investigated. The effects of Ca and S on the simulated seaside corrosion resistance of 0.1%C-1.0%Mn-0.4%Cu-1.0%Ni-0.01P-Ca-S steels were examined by CCT (cyclic corrosion test), SVET (scanning vibrating electrode technique) and Mossbauer experiments. It was found that the simulated seaside corrosion resistance of steel could be increased through Ca and S additions. Sulfur induced the rapid formation of the stable rust film and Ca was found to increase highly the corrosion resistance in the later stage. Especially, the rust layer formed in CCT tested 0.007%Ca-0.008%S steel was fully protective in 3.5%NaCl solution and thus this composition steel showed the possibility as a seaside corrosion resistant steel. The rust structures of CCT tested steels were analyzed by Mossbauer experiment and it was found that the amount of fine α-FeOOH with a diameter below 13nm remarkably increased with the increase of Ca and S contents. Ca contributed to the suppression of iron dissolution reaction by increasing the pH near the steel surface and also by enhancing the formation of fine α-FeOOH of a diameter below 13nm. Probably, Ca was assumed to activate the formation of α-FeOOH through increasing pH near the steel surface. Sulfur was thought to increase the simulated corrosion resistance by enhancing the formation of α-FeOOH under the seaside atmosphere by a similar mechanism in the case of the industrial atmosphere.