Analysis of the initial oxidation layer of W-substituted alumina-forming heat-resistant steel

High-temperature oxidation behaviour of an alumina-forming austenitic (AFA, Febalance–20Ni–14Cr–2.5Al–0.15Si–2Mn–2.5Mo–0.9Nb, in wt%) steel and W-substituted AFA steel was examined. The isothermal oxidation tests were performed on the two steels at 780°C for 2 weeks in air, which indicated that the substitution of W for Mo was beneficial to improve the oxidation resistance of the AFA steel. After oxidation at 780°C for 30 min, more compact and protective initial oxide layer against cation diffusion was formed on the W-substituted AFA steel than that of the original AFA steel, which was considered to be responsible for the reduced weight gain after the long-term oxidation.