Influence of TiO2/SiO2 and BaO/CaO ratios on viscosity, crystallization and structure of high-TiO2 mold slags for casting of high-Ti steel

Abstract

In the current study, the influence of TiO2/SiO2 and BaO/CaO ratios on viscosity, crystallization and structure of high-TiO2 mold slags was discussed through the measurement of viscosity-temperature relationship, melting temperature, crystallization temperature, crystallization rate and phases, and Raman spectrum. With the substitution of SiO2 by TiO2 in slags from 0 % to 12 %, the viscosity at 1300 °C, the melting temperature and break temperature decreased and then increased, while those of slags with the substitution of CaO by BaO from 4 % to 16 % decreased. With the substitution of SiO2 by TiO2 from 0 % to 10 %, crystallization phases gradually changed from cuspidine (Ca4Si2F2O7) to perovskite (CaTiO3), the initial and complete crystallization temperatures had the tendency to increase from 918 °C to 1260 °C and from 857 °C to 1139 °C, respectively, and the overall crystallization ability of slags increased. With the substitution of CaO by BaO from 4 % to 16 %, the initial and complete crystallization temperature of these slags decreased, and the overall crystalline ability decreased. With the substitution of SiO2 by TiO2 from 0 % to 10 %, structural units changed from the simple units to complex units, but the transition was opposite with the substitution from 10 % to 12 %, which was related to the transition of TiO2 from basic oxide to amphoteric oxide. With the substitution of CaO by BaO from 4 % to 16 %, the degree of polymerization and the viscosity of theses slags decreased, which was related to the supplement of more active O2− ion from BaO. Hence, the excessive substitution of SiO2 by TiO2 under the steel-slag reaction would cause the increase of the slag viscosity and crystallization ability, while the substitution of CaO by BaO could weaken the variation of slag viscosity and crystallization ability.