Effect of Al 2 O 3 /SiO 2 mass ratio on viscosity of CaO–Al 2 O 3 –SiO 2 –CaF 2 slag

Abstract

Recently, high Al steel has received increasing attention due to the perfect combination of strength to weight ratio and excellent ductility. The high amount of Al in the steel may cause great change on the chemical compositions of mould fluxes due to chemical reactions between SiO₂ in the mould fluxes and Al in the steel, thereby influencing the physical properties of the mould fluxes. Although many researches have reported on the effect of Al₂O₃/SiO₂ mass ratio [w(Al₂O₃)/w(SiO₂)] on the viscosity of mould fluxes, there is still a lot of controversies. In this work, the effect of w(Al₂O₃)/w(SiO₂), which is in a large range of 0·22–1·75, on the viscosity of CaO–Al₂O₃–SiO₂–CaF₂ system as a base system for mould fluxes was investigated by the rotating cylinder method. The results showed that the viscosity of CaO–Al₂O₃–SiO₂–CaF₂ system first decreases and then increases as w(Al₂O₃)/w(SiO₂) increases from 0·22 to 1·75. The viscosity values of CaO–Al₂O₃–SiO₂–CaF₂ system were also calculated by employing various viscosity models. Comparisons between calculated viscosity values and experimental data have shown that values calculated by Factsage and modified Riboud model were more close to the experimental values than other models and values calculated by the Riboud model and Shu model were much smaller than the experimental values. X-ray diffraction (XRD) analyses on the samples after the viscosity measurement indicate that there were two kinds of crystalline phase, CaF₂ and gehlenite (Ca₂Al₂SiO₇) in all fluxes and gehlenite increases with increase of w(Al₂O₃)/w(SiO₂).