Quantitative comparison of the influences of tungsten and molybdenum on the passivity of Fe-29Cr ferritic stainless steels

Abstract

The influence of tungsten on the passivity of Fe-29Cr stainless steels was compared quantitatively with that of molybdenum by examining the effects of these alloying elements on passivation parameters such as the pitting potential (E-pit), the primary passivation potential (E-pp) and the critical anodic current density (I-c) which were determined from anodic polarization responses of the alloys in a chloride or an acid solution. As the content of molybdenum and/or tungsten increased, the passive region of the alloys was expanded by increasing E-pit and simultaneously by decreasing both E-pp and I-c for the alloys. Quantitative relationships were drawn between the passivation parameters and the content of tungsten or molybdenum in the alloys. It was demonstrated that the effects of tungsten on the passivation parameters of the alloys are almost equivalent to those of molybdenum when compared on the basis of atomic per cent, a result of the similarities in chemical and electrical properties between the two elements. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.