Abstract
It is well known that the corrosion resistance of stainless steels depends on Cr depleted layer formed near the surface of matrix and the change in passive film compositions due to various surface treatments. There has, however, been little only a few quantitative studies on this phenomenon. In this study, the Cr depth profiles near the surface of SUS 304 polished mechanically and passivated in respective HNO3 solution (10, 30%), were measured by electrochemical method and AES. Then the atmospheric corrosion resistance, anodic polarization behavior in NaCl solution (Cl-: 10-2g·dm-3) and repassivation potential for crevice corrosion of SUS 304 with various Cr depth profiles were evaluated respectively. These results clarified the quantitative relation between surface Cr concentration and corrosion resistance, suggesting that the initiation process of corrosion, such as the first current increase in anodic polarization curves depends on the outermost surface Cr concentration of a passive film and the propagation process, such as rusting and the growth of pitting or crevice corrosion depends on the Cr concentration near the surface of matrix.
