Effect of Aluminium and Silicon on High Temperature Oxidation Resistance of Fe-Cr-Ni Heat Resistant Steel

Fe-Cr-Ni heat resistant steels with different contents of Al and Si were cast in intermediate fre-quency induction furnace with non-oxidation method. With oxidation weight gain method, the oxidation resis-tance of test alloys was examined at 1 200 ℃ for 500 h. The effects of Al and Si on oxidation resistance were studied through analyses of X-ray diffraction (XRD) and scanning electron microscope (SEM). It is shown that the composition of oxide scales is a decisive factor for the oxidation resistance of heat resistant steels. The com-pounded scale composed of Cr2O3, α-Al2O3, SiO2 and Fe(Ni)Cr2O4, with flat and compact structure, fine and even grains, exhibits complete oxidation resistance at 1 200 ℃. Its oxidation weight gain rate is only 0.081 g/(m2-h). By the criterion of standard Gibbs formation free energy, a model of nucleation and growth of the compounded scale was established. The formation of the compounded scale was the result of the competition of being oxidated and reduction among Al, Si, and the matrix metal elements of Fe, Cr and Ni. The protection of the compounded scale was analyzed from the perspectives of electrical conductivity and strength properties.