Mineralogical phases formed by flux glasses in continuous casting mould

Melting-solidification tests on continuous casting commercial mould flux glasses for low carbon (0.015-0.06% C) and medium carbon steels (0.07-0.1% C) revealed the existence of abundant mineralogical phases formed during the flux solidification; some important mineralogical species were identified by X-ray powder diffraction (XRD). Among the most important species found are the cuspidine (Ca₄Si₂O₇F₂) and nepheline (NaAlSiO₄). These species directly influence the heat transfer phenomena from the strand to the mould. The thermodynamic software FACTWIN was used to predict the phases formed in the fluxes considering both the chemical composition and the experimental melting temperature of the mould flux. A change in the fluidizing effect of CaF₂ was observed when the species content is higher than 12%. The phases predicted with the thermodynamic software are in agreement with those identified by XRD. It was found that cuspidine is desirable only in fluxes to produce medium carbon (included peritectic grade) steels, because it reduces the heat flux from the strand to the mould, thus controlling the shrinkage rate during the flux solidification. Liquid fluxes are required to produce low carbon steels, therefore the formation of the nepheline phase is desirable since it melts at low temperature (1073 K).