Effect of TiO2 addition on viscosity and structure of CaO–Al2O3 based mould fluxes for high Al steel casting

Abstract

High aluminium steel has received ever increasing attentions from many researchers with the perfect combination of strength to weight ratio and excellent ductility for use in automotive products. Due to addition of significant quantities of aluminium, a great challenge is to design a mould flux which is compatible with the steel and to guarantee smooth continuous casting process for ensuring the quality of billets. In this work, a mould flux of high Al steel in the casting is investigated by addition TiO2 to the flux for developing a new type of CaO–Al2O3 based mould flux. As the stability of TiO2 is stronger than SiO2, the reaction between mould fluxes and high Al steel could be reduced. The effect of TiO2 addition on the viscous behaviour of CaO–Al2O3 based mould flux for casting high Al steel were investigated by using the rotating spindle method. The water quenched glassy fluxes were analysed to identify between the structural relationship and the viscosity using Raman spectroscopy. It was found that the viscosity of fluxes decreased with the increasing TiO2 content. The SEM–EDS and X-ray diffraction analyses on the samples after the viscosity measurement indicate that there were three crystalline phases of CaO, Ca12Al14O33 and LiAlO2 in the sample free of TiO2. The addition of TiO2 leads to disappearance of CaO phase and crystallisation of perovskite phase. Raman spectral results have shown that the degree of polymerisation is reduced by increasing TiO2, which further explained the decrease in the viscosity of fluxes.