Investigation of Comparative High-Temperature Oxidation Behavior in Fe–2.2Si and Fe–6.5Si Alloys

Abstract

The differences in oxidation behavior between Fe–2.2Si and Fe–6.5Si were studied under air conditions at oxidation temperatures of 600~1150°C for 2 h. The microstructure and composition of the oxide layers were analyzed using optical microscopy, scanning electron microscopy, and other analytical techniques. Results indicate that the oxide layer of Fe–2.2Si was composed of internal oxidation layer and external oxidation layer. The thickness of the oxide layer gradually increased with rising temperature and exhibited nodulation at certain temperatures. Fe–6.5Si did not exhibit nodulation, and its oxide layer was uniformly composed of external oxidation. Below 1150°C, the oxide layer thickness remained thin, approximately 1–2 μm. For both alloys, the oxide layer thickness drastically increases at 1150°C, corresponding to the melting point of Fe₂SiO₄. This is attributed to the promotion of Fe ion outward diffusion by liquefied Fe₂SiO₄. The critical Si concentration for the transition from internal to external oxidation was calculated for both alloys. The calculated critical value for the Fe–2.2Si alloy is slightly lower than its actual Si concentration, while that for the Fe–6.5Si alloy is much lower than its actual Si.