Influence of Li₂O and Na₂O on Viscosity, Crystallization and Microstructure of High TiO₂-Containing Mold Slags

In the current study, the influence of Li₂O and Na₂O on the viscosity, crystallization, and structure of the high TiO₂-containing mold slag for the continuous casting of high-Ti steel was investigated to improve the property of the CaO–SiO₂–TiO₂-based slag under the steel-slag reaction through the measurement of the viscosity-temperature relationship, crystallization temperature and phases, and the Raman spectrum. With the increase of Li₂O content from 0 to 8 pct, the viscosity at 1300 °C and melting temperature decreased from 0.54 to 0.01 Pa s, and 1151 to 884 °C, respectively. While the viscosity of the slag at 1300 °C increased from 0.20 to 0.62 Pa s, the viscosity of the slag at 1400 °C decreased from 0.16 to 0.09 Pa s, and the melting temperature decreased from 1195 to 1077 °C with the Na₂O content from 2 to 10 pct. According to the thermodynamic calculation and XRD measurement, the main crystallization phase of high TiO₂ slags was CaTiO₃ with the content of Li₂O below 4 pct and Na₂O of 2 to 10 pct, the crystallization phase gradually changed from CaTiO₃ to LiTiO₂ with Li₂O from 4 to 8 pct, and the morphology of the crystalline nucleus changed from the type of spiky star to barbed sphere. Similarly, with the Li₂O content from 2 to 6 pct the initial and complete crystallization temperature decreased and increased, respectively, while those increased with the increase of Na₂O content, indicating that the increase of the Li₂O below 4 pct and the decrease of the Na₂O in the current slag resulted in the weak crystallization ability. With the addition of Li₂O content, the complex structural units of Q¹, Q² and Q³ were depolymerized, and the slag viscosity decreased. With the increase of Na₂O content, structural units of Q⁰, Q¹ and Q² structure units had the tendency to increase, and the viscosity of slag at 1400 °C decreased. These results could be used for the selection of typical components of mold slags for continuous casting of high-Ti steel.