The Composition of Passive Films on Ferritic Stainless Steels

Abstract

Auger electron spectroscopy has been used to investigate the influences of pH, Cl− addition, and potential on the composition of passive films on Fe‐Cr‐Mo ferritic stainless steels. It was found that the improved corrosion resistance properties obtained by the addition of molybdenum cannot be explained by its enrichment of the protective film. Molybdenum was not found in the film even at those potential and pH values at which its oxide is the stable species. However, the relative iron and chromium content in the film followed predictions based on their solubilities in aqueous solutions. These results also indicate changes in bonding in the film, as a function of distance from the substrate.