High-temperature oxidation behavior of 9Cr-5Si-3Al ferritic heat-resistant steel

To improve the oxidation properties of ferritic heat-resistant steels, an Al-bearing 9Cr-5Si-3Al ferritic heat-resistant steel was designed. We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of 9Cr-5Si and 9Cr-5Si-3Al ferritic heat-resistant steels at 900 and 1000°C. The characteristics of the oxide layer were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the oxidation kinetics curves of the two tested steels follow the parabolic law, with the parabolic rate constant kp of 9Cr-5Si-3Al steel being much lower than that of 9Cr-5Si steel at both 900 and 1000°C. The oxide film on the surface of the 9Cr-5Si alloy exhibits Cr2MnO4 and Cr2O3 phases in the outer layer after oxidation at 900 and 1000°C. However, at oxidation temperatures of 900 and 1000°C, the oxide film of the 9Cr-5Si-3Al alloy consists only of Al2O3 and its oxide layer is thinner than that of the 9Cr-5Si alloy. These results indicate that the addition of Al to the 9Cr-5Si steel can improve its high-temperature oxidation resistance, which can be attributed to the formation of a continuous and compact Al2O3 film on the surface of the steel.