Effects of Alloying Elements on the Corrosion Properties of High Strength Steel in a Sour Environment

Abstract

The effects of alloying elements (Mn, Cr, and C) on the corrosion resistance of steel were examined using weight loss test, polarization test in a sour environment, analysis of rust, and the prediction of stable corrosion product. Carbon was found to improve corrosion resistance after 7-day immersion, while manganese and chromium negatively affected the corrosion resistance of steels during the entire immersion time. The negative effect of manganese and chromium on the corrosion resistance in the sour environment was explained, in that both manganese and chromium were stable as ionic species were dissolved in the sour solution, which was proved by the prediction of stable phases based on phase equilibria. The positive effect of carbon, on the other hand, was due to the formation of amorphous carbon distributed near the metal/rust interface, which may improve the adhesion of the corrosion product to the matrix. This is consistent with not only the formation of adhesive rust on the high carbon-containing steels but also the change in the corrosion behaviour of the high carbon-containing steels, from linear to parabolic behaviour, with time.† (