Effects of Fluorine on Solidification, Viscosity, Structure, and Heat Transfer of CaO-Al₂O₃-Based Mold Fluxes

To mitigate the chemical reaction between mold fluxes and high-Al steel, CaO-Al₂O₃-based mold fluxes were proposed to replace the conventional CaO-SiO₂-based mold fluxes. However, the high viscosity of CaO-Al₂O₃-based mold fluxes is harmful to the lubrication to the strand. In this article, the effects of fluorine on solidification, viscosity, structure, and heat transfer of CaO-Al₂O₃-based mold fluxes were evaluated. The addition of fluorine increased the break temperature and decreased the heat transfer rate of mold fluxes. It also reduced the flux viscosity at 1673 K (1400 °C) when fluorine content increased from 4.0 to 6.9 mass pct; but a further increase of fluorine to 12.5 mass pct did not notably change the flux viscosity. This phenomenon was correlated to the synergic effects of the dissociation of flux network and the increased potential of nucleation at high temperature with the fluorine addition.