Role of an Impurity Element on Improvement in Steam Oxidation Resistance of High Cr Ferritic Steels

摘要

Effects of S are investigated systematically on the steam oxidation resistance of high Cr ferritic steels. It is found that the presence of S at an impurity level, about 50ppm, in the steels improves remarkably the oxidation resistance. For example, when the steels are exposed to steam atmosphere at 923K for 3.6Ms, the total thickness of oxide layers formed on the surface becomes about half as the S content in the steel increases from 10ppm to 50ppm. The enrichment of Cr together with S is observed on the surface of the S containing steels at elevated temperatures, which probably leads to the significant improvement of their oxidation resistance. These results indicate that ferritic steels with excellent steam oxidation resistance can be designed and developed by leaving S at an impurity level in them without giving any detrimental effects on the mechanical strengths.