Abstract: Vacuum Degassing (VD) refining can effectively remove gases, sulfur, and inclusions in steel. However, low-melting-point large-size non-metallic inclusions and high aluminum loss in steel occurred during VD refining in commercial production. To solve the problems, the influence of VD refining on non-metallic inclusions and aluminum loss was summarized, focusing on the formation mechanisms and controlling methods of low-melting-point large-size inclusions and aluminum-loss. The formation mechanism of large-size inclusions included the following two: exogenous by entrainment and endogenous. The entrainment-type large-size inclusions could be decreased by regulating argon stirring intensity during the later period of VD refining. While endogenous large-size inclusions could be controlled by reducing CaO activity in refining slag, increasing Al₂O₃ content in slag, decreasing [Al] content and controlling [Ca] content in steel. The aluminum loss during VD processing could be reduced by decreasing the initial aluminum content in steel, along with increasing slag basicity (CaO/SiO₂) and Al₂O₃ content appropriately.

Key words: VD refining, low-melting-point large-size inclusions, aluminum loss, steel cleanliness