Interfacial Reactions between Oxygen Containing Fe and Al at the Onset of Liquid Fe Deoxidation by Al Addition

The phenomena taking place at the early stage of Al deoxidation were investigated with specific attention on the formation of Al2O3 inclusions. In a quartz tube, Al was exposed to liquid Fe containing different amounts of dissolved oxygen ((O) under bar) for 1, 5, 30 and 60s. In this paper, quenched microstructures of the diffusion couple were examined to identify the interactions and the nature of the phases at the experimental temperature. They revealed that the reaction zone was composed of successive layers of Fe-Al intermetallic compounds, as predicted by the phase diagram of the system, i.e. alpha Fe(Al), FeAl, FeAl2, Fe2Al5 and FeAl3. Based on the microstructure, the concentration profiles, diffusion processes in solid and liquid phases, and the behavior of Al2O3 inclusions in the reaction zone, it was demonstrated that the reaction zone was completely liquid and that the solid Fe shell melted for the samples with holding time of 30 and 60 s.