Effect of Al 2 O 3 and CaO/SiO 2 ratio in slag on the cleanliness of bearing steel GCr15

This study investigates the effect of Al₂O₃ content (ranging from 30% to 38%) and the CaO/SiO₂ ratio (ranging from 4 to 7) in LF refining slag at 1600 °C on the cleanliness of bearing steel through laboratory experiments. The driving forces (concentration difference ΔC) of four inclusions (Al₂O₃, MgO-Al₂O₃, Mg₄Al₂O₇, and MgO) in the CaO-SiO₂-Al₂O₃-5% MgO slag as well as the slag viscosity (η) at 1600 °C were calculated by Factsage 8.1 software. The relationship between ΔC/η (specifically for MgO·Al₂O₃ inclusions) and the cleanliness of bearing steel was investigated. The results show that the steel-slag reaction significantly reduces the total oxygen content, inclusion number density, and area fraction within the molten steel, thereby augmenting its cleanliness. With increasing Al₂O₃ content and CaO/SiO₂ ratio in the slag, a notable trend of initial decline followed by subsequent increase is observed in both total oxygen content and total inclusion number density and area fraction within the molten steel. The LF slag composition is suggested to comprise 32% Al₂O₃, with a CaO/SiO₂ ratio of 6. The ΔC/η ratio of MgO·Al₂O₃ inclusions shows a positive correlation with the apparent rate constant of oxygen removal (k_o) while exhibiting a negative correlation with both the number density and area fraction of MgO·Al₂O₃ inclusions. This indicates that ΔC/η ratio of MgO·Al₂O₃ inclusions directly affects the removal rate of MgO·Al₂O₃ inclusions. Moreover, LF refining slag exhibits varying adsorption capacities for the four types of inclusions, ranked as Al₂O₃> MgAl₂O₄> Mg₄Al₂O₇> MgO.