| Summary: | The non-metallic inclusions in steel mainly come from the deoxidization process of molten steel. Based on the different deoxidization processes of GCr15 bearing steel produced by a domestic steel plant, the single deoxidization curves of Al, Si, and Mn and the compound deoxidization curves of Al-Si and Si-Mn under pure molten iron and GCr15 bearing steel production conditions were calculated with the FactSage 8.1 thermodynamic software. The results show that the deoxidization curves under the two conditions are quite different. At the same time, the Al-Ti deoxidation equilibrium curve under the condition of GCr15 bearing steel was calculated. It was found that when [Ti] < 0.0015% in the steel, the equilibrium deoxidation product was Al<sub>2</sub>O<sub>3</sub>, and no titanium oxide was generated. Finally, a thermodynamic calculation and analysis of the effect of rare-earth Ce content on the modification of inclusions in GCr15 bearing steel were carried out. The results showed that when T = 1873 K, the rare-earth Ce treatment of aluminum deoxidized the GCr15 bearing steel; when [Al] = 0.015%, Al<sub>2</sub>O<sub>3</sub> inclusions increased with the increase in [Ce] content, and the evolution path was Al<sub>11</sub>O<sub>18</sub>Ce→CeAlO<sub>3</sub>→Ce<sub>2</sub>O<sub>3</sub>. When [Si] = 0.28%, [O] > 50 ppm, and CeCrO<sub>3</sub> and [O] 0.012% appeared. CeS inclusions appeared in the steel, and the final equilibrium product was CeS + Ce<sub>2</sub>O<sub>3</sub>. When [Ce] < 0.012%, CeS was not produced in the steel, and only Ce<sub>2</sub>O<sub>3</sub> existed.
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