Thermophysical Properties of Continuous Casting Mold Flux for Advanced Steel Developments

The effect of Al2O3 on the crystallization and viscosity of calcium-silicate based fluxes with Na2O and Li2O additions used for continuous casting mold fluxes have been studied using the confocal laser scanning microscope and the rotating spindle rheometer. Al2O3 additions lowered the crystallization temperature of the flux and several crystalline phases for fluxes with high concentrations of SiO2 forms depending on the cooling rate. High Al2O3 containing fluxes formed relatively few crystalline phases and were not highly dependent on the cooling rate. At slow cooling rates of 25 K/min for 10 and 20 wt% Al2O3 containing samples, SEM images revealed dendrites formed within the crystalline phases. At faster cooling rates the dendrite formation is inhibited and a spherical morphology could be observed. The substitution of SiO2 with Al2O3 content modified the dominant silicate network into complex alumino-silicates. This increased the viscosity of the melt. FTIR and Raman analysis showed increased amounts of symmetric Al–O0 stretching with higher Al2O3. With higher CaO/(SiO2 + Al2O3), the symmetric Al–O0 stretching and the Si–O–Al seems to decrease.