The effects of BaO and Na₂O on the viscosity and structure of CaO–SiO₂–MgO–Al₂O₃-based blast furnace slag were investigated using the rotating cylinder method and Raman spectra technique in this work. The results indicated that the slag viscosity first increased and then decreased with the addition of BaO and decreased with the increasing content of Na₂O. When adding BaO into CaO–SiO₂–MgO–Al₂O₃ slag, Ba²⁺ ion could compensate Al³⁺ ion and form more complex aluminate or aluminate–silicate structures, which increased the degree of polymerisation and the viscosity of the slag. With the further addition of BaO, the content of SiO₂ decreased and the relative content of O²⁻ ion increased, which may slightly depolymerise the slag structure then decreased the viscosity. When adding Na₂O into CaO–SiO₂–MgO–Al₂O₃–BaO slag, Na₂O may act as network modifiers which could simplify the complex silicate structures and lower the polymerisation degree of slags, therefore decreased the viscosity.

The corrosion behaviors of corundum brick and carbon composite brick used in blast furnace hearth by CaO–SiO2–MgO–Al2O3–Cr2O3(-CaF2) slags were studied in the present work. The degradation of the corundum brick in slag was a result of slag infiltration and brick dissolution, and the corrosion of the brick became more serious with the addition of CaF2 due to the decrease of slag viscosity. The disintegration of carbon composite brick in CaF2-containing slag was caused by the combination of slag penetration, brick dissolution and reaction between slag and brick. By comparing the corrosion behavior in CaF2-containing slag between the corundum brick and carbon composite brick, the corrosion degree of the corundum brick was greater than that of the carbon composite brick. To the blast furnace operation in which a low grade iron ore such as laterite ore and CaF2 containing slag (about 2 wt%) are used, it was found that the carbon composite brick with better slag corrosion resistance can be selected as a hearth refractory so as to improve the operation performance and ensure the longer campaign life of blast furnace.

Al₂O₃, Al₂O₃·TiN, Al₂O₃·MgO, and CaO·2Al₂O₃ are four different types of inclusions in high Al steels. To improve the steel cleanness level, the effective removal of such inclusions during secondary refining is very important, so these inclusions should be removed effectively via inclusion dissolution in the slag. The dissolution behavior of Al₂O₃, Al₂O₃·TiN, Al₂O₃·MgO, and CaO·2Al₂O₃ in CaO-SiO₂-Al₂O₃-MgO slags, as well as the steel-slag reaction, was investigated using laser scanning confocal microscopy (LSCM) and high-temperature furnace experiments, and thermodynamic calculations for the inclusion in steel were carried out by FactSage 7.1. The results showed that Al₂O₃·TiN was observed to be completely different from the other oxides. The composite oxides dissolved quickly in the slags, and the dissolution time of the inclusions increased as their melting point increased. SiO₂ and B₂O₃ in the slag were almost completely reacted with [Al] in steel, so the slags without SiO₂ showed a positive effect for avoiding the formation of Al₂O₃ system inclusions and promoting inclusions dissolution as compared with SiO₂-rich slags. The steel-slag reaction was also found to influence the inclusion types in steel significantly. Because of the rapid absorption of different inclusions in the slag, it was found that the dissolution time of inclusions mainly depends on the diffusion in the molten slag.