Effect of N substitution for Ni on the high-temperature oxidation resistance of GX40CrNiSi25-12 austenitic heat-resistant steel

Abstract

In this paper, the effect of nitrogen (N) substitution for nickel (Ni) on the high-temperature oxidation resistance of austenitic heat-resistant steel was investigated based on GX40CrNiSi25-12 austenitic heat-resistant steel. The study also analyzed the differences in oxidation resistance among the test steels using oxidation thermodynamics and kinetics, as well as investigated how the morphology and structure of the oxide film impact high-temperature oxidation resistance. The results indicated that the introduction of the N element facilitated the formation of a protective oxide layer within the test steel, which impeded further reactions between the internal metal elements and external oxygen. The uniformly formed SiO₂ oxide layer significantly enhances the adhesion of the oxide film to the substrate, effectively preventing the shedding of oxides. Additionally, N promotes the development of chromium (Cr)-rich bands, which play a crucial role in inhibiting the growth of surface oxides and reducing the overall thickness of the oxide film. Moreover, the presence of N leads to improved densification of the surface oxide layer. This dense structure is instrumental in restricting ion diffusion, thereby decreasing the weight gain rate associated with high-temperature oxidation in the tested steel. Specifically, when the nitrogen content reached 0.32%, the oxidized weight gain and weight gain rate were reduced by 76.6% and 76.9%, respectively, compared to the steel without N addition. In conclusion, the substitution of nitrogen for nickel provides a highly effective means of enhancing the high-temperature oxidation resistance of austenitic heat-resistant steel. This research offers valuable insights for the future design of Ni-saving austenitic heat-resistant steel materials.