Effect of Al content on the high-temperature oxidation behavior of 18Cr–Al–Si ferritic heat-resistant stainless steel

Abstract The effect of Al content on the high-temperature oxidation (800 and 900 °C) of 18Cr–Al–Si FHSS (ferritic heat-resistant stainless steel) for up to 180 h in air was investigated via the isothermal oxidation method. The oxidation kinetic curves followed a parabolic law. A higher Al content reduced the oxidation rate and improved the oxidation resistance and also promoted the formation of a denser and more continuous Al2O3 film during the early oxidation stages, which provided an effective barrier that hindered the diffusion of oxygen into the matrix. The oxide films that formed on the 0.63Al FHSS and 1.06Al FHSS were composed of spinel MnCr2O4 in the outer layer, MnO and Cr2O3 in the middle layer, and Al2O3 and SiO2 in the inner layer. The middle layer of 0.63Al FHSS also contained a small amount of Fe2O3. The oxidation mechanism was also discussed based on oxidation kinetics, morphological observations, and phase analysis of oxide films.