Viscosity and surface tension of CaF2–CaO–Al2O3-based slag with varying SiO2 and B2O3 contents for ESR of rotor steel

The effect of SiO₂ and B₂O₃ on viscosity and surface tension of CaF₂–CaO–Al₂O₃–MgO–SiO₂–B₂O₃ slag designed for electroslag remelting of rotor steel was investigated. The viscosity of the slag melts increases with increasing the SiO₂ content from 0.37 to 8.03 mass%, and the viscous activation energy increases from 54.21 to 58.49 kJ/mol. Increasing B₂O₃ content of the slag from 0 to 3.62 mass% exhibits a similar effect on the viscosity, and the activation energy increases from 47.30 to 55.71 kJ/mol. The increase in the viscosity and activation energy for viscous flow of slag is attributed to the enhanced polymerization degree of slag melts network with increasing either SiO₂ or B₂O₃ content. The surface tension of slag melts decreases with increasing temperature. The surface tension of slag melts decreases with increasing either SiO₂ or B₂O₃ content, which is originated from the increase in the polymerization degree and the decrease in the CaO content of the slag.