Effects of non-metallic inclusions on the initiation of pitting corrosion in 11% Cr ferritic stainless steel examined by micro-droplet cell

This paper explores the effects of non-metallic inclusions (NMIs) on the initiation of pitting corrosion in type 409L stainless steels refined by the argon oxygen decarburization (AOD) and vacuum oxygen decarburization (VOD) processes. The dominant NMIs in the AOD and VOD samples were (Ti, Ca)-oxides and Ti-nitrides, respectively. In-situ electrochemical noise (EN) and micro-electrochemical analyses were conducted to investigate quantitatively the inherent effects of the NMIs on the pitting corrosion of the alloys. Pitting corrosion was initiated mostly around the (Ti, Ca)-oxides in the AOD samples, while little such corrosion occurred around the Ti-nitrides in the VOD samples. In addition, the pitting resistance of the AOD samples increased with increasing Ti content and decreasing Ca content in the (Ti, Ca)-oxides.