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

Abstract

The viscosity of SiO₂–30Al₂O₃–B₂O₃–12Na₂O–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 ΔT_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 −25 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 ∼13%.

Keywords:

• Viscosity
• B₂O₃
• Break temperature
• FTIR

Acknowledgements

The authors gratefully acknowledge financial support by the Common Development Fund of Beijing and the National Natural Science Foundation of China (grant nos. 50902003 and 51172003). Supports by the National High Technology Research and Development Program of China (863 Program, grant no. 2012AA06A114) and Key Projects in the National Science & Technology Pillar Program (grant nos. 2011BAB03B02 and 2011BAB02B05) are also acknowledged.