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

Abstract

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%.

Keywords

• bearing steel
• refining
• slag composition
• basicity
• inclusions
• thermodynamic analysis