Effect of Molybdenum on the Pitting Potential of High Purity 18% Cr Ferritic Stainless Steels

The anodic behavior of high purity 18% Cr ferritic stainless steels, with a content from 0 to 5% molybdenum, was studied in and in solutions. The studies were complemented by Auger electron spectroscopy analysis of the films in solutions. It was found that the effect of molybdenum on the pitting potential of these alloys in solutions could be rationalized assuming that pit initiation is related to localized acidification at the metal‐solution interface. The Auger analysis showed a high concentration of chloride ions in the films formed in solutions. No molybdenum enrichment was found in the films. The anodic behavior of these alloys in solutions was related to the formation of a slowly dissolving salt layer of on the alloy surface. The results suggest that molybdenum exerts its influence by reducing the dissolution rate of the salt layer.