Oxide Films on Stainless Steels★

Abstract

Abstract Oxide films on stainless steels have been classified into three types according to film thickness, film structure, film composition, and influence of the film on resistance to corrosion. Compositional properties of oxide films isolated from surfaces of stainless steels were studied using specially developed microanalytical techniques. Properties of passive films on stainless steel were evaluated and the effects of alloy composition and surface treatment on other types of films on Types 304, 316, and 347 stainless steels were studied. The influence of corrosion in various media was correlated with film compositional properties. Composition of films after immersion in acids was found to be related to film composition prior to immersion. The effect of immersion depended on the nature and intensity of corrosion and was reflected most sensitively by the iron and silicon contents of the films. The conclusion was made that film properties indicate strongly the capacity of austenitic stainless alloys to develop corrosion-resistant surfaces in certain environments.