Effect of B2O3 addition on viscosity of mould slag containing low silica content

The viscosity of SiO2-30Al(2)O(3)-B2O3-12Na(2)O-CaO slag system (CaO/SiO2=2.68-7.35, B2O3=0-9 wt-%) was investigated in the present study. The objective is to study the influence of B2O3 on the viscosity and structure of mould slags containing low silica content. The research of the low silica slag system is meaningful because of it is less reactive with Al during continuous casting of steels containing high amounts of dissolved aluminium, such as transformation induced plasticity assisted steels. The viscosities of these quinternary slags decreased slightly with an increase in the content of additive B2O3 above the break temperature. The apparent activation energy of viscous flow was found to decrease with increasing B2O3 content. The break temperature also decreased with increasing B2O3 content. Based on the experimental data, the decrease in break temperature per mol.-% B2O3 Delta T-br is 15.23 K. An empirical model was then established to predict the break temperature of mould slags containing B2O3, and the deviation is between 225 and +25 K. Based on the viscosity and Fourier transform infrared analysis, it is proposed that the three-coordinated boron is dominated in these slags over the entire compositional range, and the borosilicate networks are loosened with increasing B2O3 content in the present study. The Riboud model was modified empirically based on the present experimental data, and the mean deviation is similar to 13%.