Abstract: The thermodynamic software FactSage 7.0 and industrial practice were applied to study the formation of non-metallic inclusions in GCr15 bearing steels during deoxidation process at 1 873 K. Calculated results show that inclusions in molten steel shift Al2O3 to MgO•Al2O3 when the [Mg] mass fraction is larger than 1×10-6. Solid MgO inclusions form when the [Mg] mass fraction is over 10×10-6. Solid CaO•6Al2O3 and CaO•2Al2O3 inclusions generate when the [Al] mass fraction is over 100×10-6 and the [Ca] mass fraction is over 0.1×10-6. Liquid calcium aluminate and solid CaO inclusions appear when the [Ca] mass fraction exceeds 2×10-6 and 13 ×10-6, respectively. Thermodynamic calculated results are in good agreement with measured ones. Besides, evident deviations of deoxidation thermodynamics between pure iron and bearing steel are found, indicating that thermodynamics of pure iron can’t be used to guide the production of bearing steels.

Key words: bearing steel, inclusion formation, thermodynamics, industrial practice