Effect of Nickel Addition on the Corrosion Resistance of Steel in a Subtropical Seashore Environment

This study investigated the effects of Ni addition on the corrosion resistance of steel in subtropical seashore environments. Carbon steel and 3, 5, and 7% Ni steels were exposed in such an environment for a year. Addition of Ni depressed the corrosion rate of steels and number of cracks in the rust layer. Quantitative and three-dimensional measurement of the cracks with a wide range of widths and volumes in the rust layer was carried out for the exposed steel specimens using the mercury intrusion method. The total crack volume in the rust layers on 5% Ni steel was 60% lower than that for the carbon steel. It is considered that rust layers with less crack volume suppressed Cl- migration through the rust layer. The CI concentration near the metal interface was relatively lower in the 5% Ni steel by EPMA analysis. And the rust layer on 5% Ni steel also showed a higher permeation resistance than that formed on carbon steel. Considering the formation of rust layers with less volume crack on Ni-added steel based on Morcillo's model, it is concluded that the Ni addition promoted the formation of a-FeOOH and suppressed the reduction of gamma- and beta-FeOOH, thus resulting in a more intact rust layer.