Thermodynamic analysis of the relationship between refining slag composition and inclusion type in bearing steel

In order to control large calcium aluminate inclusions in bearing steel, the quantitative relationship between refining slag composition and inclusion type is discussed by calculating the formation thermodynamics of MgO·Al₂O₃ and CaO·6Al₂O₃ in this paper. The results show that MgO·Al₂O₃ can be reduced to CaO·6Al₂O₃ by dissolved aluminum with 0.10×10^-6 Ca and less than 10×10^-6 Mg in molten steel. When the basicity of refining slag is 7.04 and the content of (MgO) is 1.38%, the content of Mg in liq-uid steel is about 56% lower than the critical value, and the main inclusions is CaO-Al₂O₃, whose dimension is larger than 10μm. As the basicity of refining slag is 3.75 and the content of (MgO) is 3.14%, the content of Mg in liquid steel is about 14% lower than the critical value, and the main inclusions is MgO·Al₂O₃ surrounded by MnS, whose dimension is less than 8μm. Under the condition that the Ca/Al ratio is between 1.8 and 2.0, MgO·Al₂O₃ inclusions can be kept stable rather than reduced to CaO·6Al₂O₃ when the basicity of refining slag is between 4.5 and 5.5 and the content of MgO is between 3% and 5%.