An XPS and electrochemical study of the influence of molybdenum and nitrogen on the passivity of austenitic stainless steel

In previous surface studies of N bearing stainless steels exposed to acidic environments we have determined that N is anodically segregated as a surface nitride phase. In this paper we have focused on the nature of the surface nitride and its role in the passivity of each of the constituent elements comprising a Mo bearing stainless steel. To facilitate this study, surface nitrides were generated electrochemically at room temperature on the surface of high purity samples of Cr, Mo, Fe and Ni and on the surface of types 304, 317LX, 904L and AL6X stainless steels. The effect of the surface nitriding treatment on the anodic kinetics of the stainless steels was in close agreement with the effect of N alloying. The surface nitriding of Cr resulted in the complete elimination of the active nose in deaerated 0.1 M HCl. Mo and Ni showed only small effects of surface nitriding, while Fe exhibited higher rates of anodic kinetics. The mechanism by which surface nitrides modify the anodic kinetics of stainless steel is discussed.