Enhancing oxidation resistance of a novel nickel-saving dual-phase heat-resistant cast steel based on Mn–N optimized oxide scale

The effect of Mn–N on the oxidation behavior and microstructure evolution of a novel nickel-saving Fe–26Cr–4Ni-0.3C dual-phase heat-resistant cast steel at 900 °C was investigated. After 100 h of oxidation, the H–Mn–N steel (3.14 %Mn-0.232 %N) exhibited approximately three times better oxidation resistance compared to the L-Mn-N steel (0.24 %Mn-0.084 %N). The increase of Mn–N decreased the oxidation rate from 2.30 × 10−2 mg2 ∙ cm−4 ∙ h−1 to 3.26 × 10−3 mg2 ∙ cm−4 ∙ h−1. The oxide scale structure of L-Mn-N steel consisted of outer Cr2O3, inner (Fe0.6Cr0.4)2O3, and Fe1.4Cr1.6O4, while the oxide scale of H–Mn–N steel (3.14%Mn) was SiO2, MnCr2O4, and Mn1.5CrO4 from the matrix to the outside. Mn–N increased the proportion of austenite from 40 % to 70 %, which reduced the diffusion rate of oxygen. This hindered the formation of layered oxide Cr2O3 and promoted the formation of a dense layer of SiO2 on the matrix surface, providing a pathway for the enhancement of the trade-off between oxidation resistance and cost.