Effect of high basicity refining slag on the cleanliness of high-carbon chromium bearing steel

The effect of high basicity (CaO/SiO₂ ratio) refining slag on the cleanliness of high-carbon chromium bearing steel was investigated systematically by steel-slag equilibrium experiments through a high temperature Si-Mo resistant furnace. The binary slag basicity was increased from 3 to 5, 7, and 9, with the mass ratio of CaO to Al₂O₃ in slag was maintained at 1.93. The experimental results showed that increasing slag basicity enhances CaO activity while suppressing Al₂O₃ activity, thereby significantly improving the slag's inclusion removal and modification capabilities. As the slag basicity increased from 3 to 5, 7, and 9, the total oxygen (T.O) content in steel specimen was measured to be 10 ppm, 9 ppm, 9 ppm, and 5 ppm, respectively, and the inclusion number density was counted as 14.7 #/mm2, 4.8 #/mm², 5.5 #/mm², and 1.7 #/mm², indicating that relatively high slag basicity is beneficial to improving the cleanliness of bearing steel. Notably, this study introduces an innovative three-dimensional (3D) inclusion stability diagram methodology that overcomes the limitations of conventional 2D diagrams. The proposed 3D diagram retains three independent thermodynamic variables, enabling more comprehensive analysis of inclusion formation mechanisms in complex multicomponent systems. This methodological advancement provides an enhanced predictive capability for inclusion evolution as well during the refining process.