Influence of Temperature and Composition of SO_2/O_2 Atmosphere on the Surface Morphology of Alumina Scales Formed on FeCrAl Steel

摘要

The paper deals with the oxidation of an FeCrAl-type steel in SO_2 and in SO_2/O_2 gas mixtures in the temperature range 800 - 850℃. It has been found that at 850℃, independently of the composition of the oxidizing atmosphere, the α-Al_2O_3 scale is strongly deformed and poorly adherent to the metallic substrate. At lower temperatures (800-830℃), the scale is adherent and composed of α-Al_2O_3 and θ-Al_2O_3, with a characteristic plate-like morphology of the external surface. At 820℃, in the atmospheres containing less than 60% SO_2, the plate-like structure tends to disappear and the rate of scale formation increases with the concentration of O_2 in the SO_2/O_2 mixtures. In SO_2 and in the SO_2/O_2 mixtures containing more than 95% SO_2, a well-developed plate-like structure is observed and its mass is comparable to the mass of the inner compact layer of α-Al_2O_3.