Effect of caf2 on the viscosity and microstructure of CaO-SiO2-Al2O3 based continuous casting mold flux

Abstract

In this study, a CaO-SiO2-Al2O3-based continuous casting mold flux was designed using the FactSage thermodynamics software to determine the composition range of CaF2. The viscosity characteristics of the mold flux were determined using a rotating viscometer. The results show that the constant temperature viscosity at 1300 °C decreases gradually as CaF2 content is increased from 3% to 11% in the CaO-SiO2-Al2O3-based slag. Viscosity is reduced from 0.854 to 0.241 Pa·s, viscous the flow activation energy is reduced from 157.74 to 114.34 kJ·mol−1, and the break temperature is reduced from 1280 to 1180 °C. Furthermore, when the CaF2 content is increased from 3% to 11%, the number of nonbridging fluorine bonds (Al-F structure and Si-F structure) in the melt increases to 287, the number of bridging fluorine bonds (Al-F-Al structure, Si-F-Si structure, and Si-F-Si structure) is only 17, and the network rupture of fluorine ions in the system is larger than the network formation. Consequently, both the degree of polymerization and viscosity are reduced.