Influence of Al on scale formation and growth kinetics of 10 wt.% Cr creep resistant ferritic steels at 650 °C in air

Two 10 wt.% Cr steels containing 1.90 and 2.33 wt.% Al respectively were oxidised in air at 650 °C. The scales formed on the steel with 2.33 wt.% Al were θ-Al2O3 and α-Al2O3 with differing parabolic rate constants. The scales formed on the steel containing 1.90 wt.% Al consisted of multiple layers of Fe-oxides and the amount of oxidation followed logarithmic kinetics Δmt = klln(t/t0 + 1). An empirical model was obtained for calculating the minimum amount of Al needed for forming an external Al2O3 scale on Fe-10Cr-xAl (wt.%) alloys in air in 650-1050 °C.