Initial morphology of atmospheric corrosion on Ni and Cr additive steel

The corrosion characterization of the low alloy steel under seashore environment depends on the alloy elements. Rusting process and corrosion behavior of pure iron, Fe-3 mass%Ni and Fe-3 mass%Cr low alloy steel under corrosion cycle test were investigated by surface observation using optical microscope, laser microscope and AFM. Both Ni and Cr were effective to decrease the corrosion rate and the filiform corrosion type that is the same to the case of pure iron occurred on the alloys during rusting process. Form the result of removing the rust, the pitting corrosion was appeared under the rust on the Cr additive steel although the general corrosion occurred in the case of pure iron and Ni additive alloy. The difference of the corrosion type was explained by hydrolysis equilibrium. Fe and Ni anodic dissolution did not make the pH decline. When the anodic dissolution of Cr was carried out, it is easy to decline pH and severe condition was achieved at the local site. Therefore, localized corrosion produced on the Fe-Ce alloy.