2017 Volume 66 Issue 8 Pages 273-281
It is well known that precipitates on the surface of stainless steels would be initiation points of pitting corrosion. In this study, it was investigated that an effect of Cu precipitates with tens of nm diameter on early stage corrosion and pit initiation of stainless steel. The diameters of Cu precipitates in 18％Cr-3％Cu ferritic stainless steel were controlled by aging condition which are 500-700℃, 1-100h, and the diameters were 0-51nm in grain and 104-125nm at grain boundary. In pitting potential measurement, the Cu precipitates on the surface of specimens were dissolved below pitting potential. It was suggested that the holes formed by the dissolution of the Cu precipitates initiated pits at pitting potential. Pit density of the pitting potential measurement had correlation with number of corrosion point in cyclic corrosion test. The pit densities of specimens with intragranular Cu precipitates whose average diameters were more than 35 nm were larger than that of specimens with less than 35 nm diameter precipitates. Therefore, it was suggested that there is a critical diameter of Cu precipitates which can affect pit initiation.
