Effect of Na2O on crystallisation behaviour and heat transfer of high Al steel mould fluxes

The reaction between [Al] and SiO2 leads to compositional changes in mould fluxes during continuous casting of high Al steel. These changes result in the decrease in SiO2 and the increase in Al2O3 contents, as well as the rapid increase in the basicity [w(CaO)/w(SiO2)] of the mould fluxes. The slag rim is developed excessively such that the fluxes cannot infiltrate into the gap between the mould and the strand. In this study, therefore, non-reactive mould fluxes were designed, and the effect of Na2O on the crystallisation and heat transfer of these fluxes was investigated via single hot thermocouple technique, heat flux simulation and scanning electron microscopy. With the increase in Na2O content, the critical cooling rate and crystallisation rate constants were inhibited, and the incubation time increased. Na2O restrained the crystallisation of non-reactive mould fluxes. The maximum heat flux, the average heat flux and the characteristic time rose with the increased Na2O content.