Influence of CaF₂ and Li₂O on the Viscous Behavior of Calcium Silicate Melts Containing 12 wt pct Na₂O

Understanding the viscous behavior of silica-based molten fluxes is essential in maintaining the reliability of steel casting operations and in preventing breakouts. In particular, high concentrations of aluminum in recently developed transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) steels tend to promote reduction of silica in the mold fluxes that result in the formation of alumina, which in turn increases the viscosity. To counteract this effect, significant amounts of fluidizers such as CaF₂ and Li₂O are required to ensure that mold fluxes have acceptable lubrication and heat transfer characteristics. The viscous behavior of the slag system based on CaO-SiO₂-12 wt pct Na₂O with various concentrations of CaF₂ and Li₂O has been studied using the rotating spindle method to understand the effects on the viscosity with these additives. CaF₂ additions up to 8 wt pct were effective in decreasing the viscosity by breaking the network structure of molten fluxes, but CaF₂ concentrations above this level had a negligible effect on viscosity. Li₂O additions up to 2 wt pct were also effective in decreasing the viscosity, but the effect was comparatively negligible above 2 wt pct. Using Fourier transform infrared (FTIR) analysis of as-quenched slag samples, it was concluded that the viscosity was controlled more effectively by changing the larger complex silicate structures of rings and chains than by changing the amounts of simpler dimers and monomers.