The Effect of Chromium Content (0 to 35%) in Fe–Cr Alloys on Corrosion Rates and Mechanisms in 1.0 N Sulfuric Acid

Abstract

The effect of chromium content (0 to 35 percent) in Fe–Cr alloys on their dissolution in 1.0 N sulfuric acid was investigated. Corrosion rates increase with increasing chromium content. Corrosion rates were determined by three electrochemical technigues (Tafel extrapolation, three-point, and polarization resistance methods) and were compared with the rates determined by weight-loss measurements. The cathodic hydrogen evolution reaction is independent of the chromium content; that is, the exchange current density (io) and the Tafel slope (βc) are essentially constant with changes in chromium content. The anodic Tafel constant (βa) for alloy dissolution is also independent of the chromium content. The increase in corrosion rates observed with increasing chromium content is directly proportional to the change in the active direction of anodic open-circuit potential and, therefore, also the corrosion potential in this case. Some effects of this phenomenon on pitting and crevice corrosion in chloride solutions are discussed.