The conventional CaO-SiO2-based mould fluxes are not suitable for high-Al steel casting because
of the strong reaction between silica in the flux and aluminium in the steel strand. In the process of
casting of high-Al steel, flux composition changes; with the decrease of the silica concentration and
increase of alumina. Knowledge and understanding of the effect of the Al2O3/SiO2 ratio on flux
structure and properties are useful for flux design for the high Al-steel continuous casting.
This paper investigated the effect of the Al2O3/SiO2 ratio on structure, viscosity, phase composition
of fluxes quenched at different temperatures and heat transfer of CaO-Al2O3-SiO2-B2O3-Na2O-Li2OMgO-
F fluxes. It was found that flux melting temperature increased with the increase in Al2O3/SiO2
ratio. Viscosity of the flux melts increased significantly with the increase of the Al2O3/SiO2 ratio from
0.7 to 1.2, reaching the maximum value, and then decreased with further increase of the Al2O3/SiO2
ratio. Raman spectroscopy analysis revealed that the change of the Al2O3/SiO2 ratio led to the
change of aluminate and silicate structural units. The turning point for viscosity was attributed to the
change in the degree of flux polymerisation. X-ray diffraction (XRD) analysis showed that increasing
Al2O3/SiO2 ratio increased crystallisation tendency of the fluxes. Heat transfer measurement by
infrared emitter technique (IET) revealed that increasing Al2O3/SiO2 ratio led to the decrease in heat
flux which is correlated well with the increased crystallinity of the flux. The results suggested that the
flux with Al2O3/SiO2 ratio 4.3 is the best candidate among the studied CaO-Al2O3-based mould fluxes
for casting of high-Al steel.