Development of Low-Fluoride Slag for Electroslag Remelting: Role of Li₂O on the Viscosity and Structure of the Slag

Abstract

The effect of the substitution of CaF₂ with Li₂O on the viscosity and structure of low-fluoride CaF₂-CaO-Al₂O₃-MgO slag was studied with an aim to develop low-fluoride slag for electroslag remelting. Increasing Li₂O addition up to 4.5 mass pct was observed to significantly reduce the slag viscosity monotonically. Increasing temperature significantly lowered the viscosity of slag, whereas this influence is less effective with increasing Li₂O content especially above 3.5 mass pct. The activation energy for viscous flow decreases with increasing Li₂O content. The polymerization degree of aluminate networks decreased with increasing Li₂O content, as demonstrated by Raman analysis. The dominant structural unit in [AlO₄]⁵⁻-tetrahedral network is ${\text{Q}}_{\text{Al}}^{4}$. The amount of symmetric Al-O⁰ stretching vibrations significantly decreased with increasing Li₂O content. The relative fraction of ${\text{Q}}_{\text{Al}}^{4}$ in the [AlO₄]⁵⁻-tetrahedral units shows a decreasing trend, whereas ${\text{Q}}_{\text{Al}}^{2}$ increases with the increase in Li₂O content accordingly. The change in slag viscosity with chemistry variation agrees well with the changes in slag structural units.