Initiation of pitting at severe crevice of titanium carbonitride/matrix boundary on ferritic stainless steels

It has been reported that titanium carbonitrides could be a initiation site of pitting corrosion even at high corrosion resistance ferritic stainless steels such as Ti added stainless steels. However, it is hardly found any observations from the viewpoint of pre- and post-pitting corrosion related with the inclusion. Therefore, the pitting corrosion behavior in the vicinity of titanium carbonitride has not fully understood yet. The objective in this study was to clarify the inititation behavior of pitting at titanium carbonitride by means of in the test solution AFM observation under a potentiostatic condition. As a result, it was found that pitting corrosion initiated at a severe crevice which formed by polishing or rolling at titanium carbonitride/matrix boundary, with a size of several tens of nm in depth and several hundreds of nm in width. And then, the pitting corrosion grew toward depth direction of matrix side with time.