EFFECT OF HYDROGEN PRE-ANNEALING ON HIGH- TEMPERATURE OXIDATION OF FE-20CR-5AL ALLOY

The effect of pre-annealing on the oxidation behavior of Fe-20 mass%Cr -5 mass%Al alloys containing up to 0.11 mass%La was examined by a cycl ic oxidation test at 1423 K in air. SIMS and chemical analysis were ca rried out for thin oxide layers formed by pre-annealing and Al2O3 scal es formed by oxidation. The oxidation rate of La-added Fe-20%Cr-5%Al a lloys was decreased markedly by hydrogen annealing, while that of La-f ree alloy was not changed. La enrichment was found in both the thin ox ide layer formed on the alloy annealed in hydrogen and the Al2O3 scale formed on that alloy. It is concluded that La enrichment in the oxide film formed during hydrogen annealing suppresses the inward diffusion of oxygen through the Al2O3 scale, resulting in a decrease in the oxi dation rate.