Abstract:Based on the thermodynamic data and the coexistence theory of slag structure, the slag components can be calculated when the reaction between slag and molten steel is balanced according to the chemical composition of GCr15 bearing steel. According to the calculating model which is almost the same with practical results, controlling the dissolved aluminum content with 0.01%- 0.03%, the dissolved calcium content with 0.00003%- 0.00005% and the dissolved magnesium content with 0.00002%- 0.00004%, the dissolved oxygen content will be under 0.0005%. And the corresponding refining slag components are approximately as follows: w(CaO)=50%- 60%,w(MgO)=2%- 4%,w(SiO2)=10%- 25%,w(Al2O3)=10%- 35%, concentrations of FeO and MnO are nearly zero.