Effect of B2O3 on Melting Temperature of CaO-Based Ladle Refining Slag

B2O3 is selected as fluxing agent of CaO-based ladle refining slag to decrease the melting temperature as well as to improve the speed of slag forming and the refining efficiency. The effects of B2O3 on the melting temperature of two series of refining slags including the low basicity slags (the mass ratio of CaO/SiO2 is 3 — 4) and the high basicity slags (the mass ratio of CaO/SiO2 is 5 — 8.75) were investigated. The slag melting temperature was measured using the hemisphere method. The results indicate that the fluxing action of B2O3 is better than that of CaF2 and Al2O3. For the CaO-based refining slag with low basicity, the melting temperature is decreased effectively when B2O3 is used to substitute for equal mass of CaF2, Al2O3 and SiO2, respectively. For the CaO-based refining slag with high basicity, when CaF2 is substituted by B2O3, the melting temperature can be decreased remarkably. Especially, when the mass ratios of CaO/Al2O3 and CaO/SiO2 are in the range of 1.1 — 4.0 and 5.25 — 8.0, respectively, the slag melting temperature is lower than 1 300 °C. Therefore, the B2O3-containing refining slags with high ratios of CaO/Al2O3 and CaO/SiO2 have ultra low melting temperature.