18Crステンレス鋼表面における自然不動態被膜

—耐食性の発現要因とその場環境における構造変化—

抄録

All the stainless steels have specific “native passive films” formed on the surfaces. Previously, we have elucidated that the passive film on SUS304, typical 18Cr stainless steel, consists of a Cr(IV) oxyhydroxide (-O-Cr-OH-) network structure and Cr₂O₃deposited near the film/SUS interface: This dense passive film prevents bulk Fe-components from dissolving into the surface-adsorbed water. In this paper, we give explanations for the passive film on the SUS440C (18Cr-1C) surface, comparing with the case of SUS304 (18Cr-8Ni). As a result, due to the carbon components in SUS440C, fragmentation of Cr oxyhydroxide is promoted in the passive film. Therefore, the corrosion resistance of SUS440C becomes less than that of SUS304. Additionally, we report an interesting structural change of the SUS304 passive film observed by using in-situ total reflection X-ray absorption spectroscopy.