Surface oxide layer within crevices of 316L stainless steels in 561K pure water

Soma, Yasutaka   ; Kato, Chiaki   ; Yamamoto, Masahiro 

Surface oxide layers were formed within crevices of type 316L stainless steels in pure water at 561 K and 8 MPa. Cross-sectional structures of the surface oxides were analyzed using transmission electron microscopy. Under the condition of a dissolved oxygen concentration of 2 ppm, the properties of the surface oxide layer changed with the crevice position and dual or triplex layered oxides were formed, which had not been observed on a boldly exposed surface. The thickness of the inner oxide layer showed a local maximum at a certain distance from the crevice mouth. These oxide characteristics suggest the presence of locally varying electrochemical conditions. Potential-pH diagrams of the multilayered oxides suggest that the potential decreased at the early stage of exposure and then re-increased, accompanied by weak acidification.