Controlling Step Variation in the Reaction of High-Al Steel and CaO-SiO₂-Type Mold Flux

The fluid flow, species transport, and chemical reaction of high-Al steel and mold flux are simulated by a numerical model. The reactants on the species concentration evolution and the controlling step variation are investigated. The results show that much heat is generated with the chemical reaction and the fluid flows with the thermal force, which enhances the species transfer. In the later stage, less heat is produced and the liquid velocity declines, so the mass transfer rate is reduced. The mass transfer rate isn’t constant, but it varies in the reaction process. As the Al content decreases from 1.77 to 0.59 wt pct, the species concentrations are obviously changed. Since the maximum mass transfer rate of SiO₂ is larger than that of Al, the Al diffusion is the controlling step in the whole reaction period. With the initial SiO₂ content decreasing from 33.6 to 11.2 wt pct, the maximum mass transfer rate ratio of SiO₂ is lower than that of Al, especially in the later reaction stage. It means the controlling step changes from the Al diffusion to the SiO₂ diffusion with the lower SiO₂ concentration.