Passivity and its breakdown on stainless steels and alloys

The service reliability of stainless steels and alloys is predominantly determined by the chemical stability of an ultrathin passive film on their surfaces. The thickness, composition and structure of such an ultrathin oxide film are all influenced by the alloy composition and the nature of the environments they are exposed to. Surface analysis of passive films formed on different grades of stainless steels under different conditions showed that chromium was significantly enriched in the surface film whereas nickel was not present in the oxidized state. Breakdown of passivity either due to mechanical damage or due to chemical attack often leads to localized corrosion in the form of pitting, crevice corrosion and stress corrosion cracking. This paper discusses the corrosion resistance characteristics of stainless steels and alloys in the context of surface film properties.