Effect of refining slag basicity on removal of large size inclusions in GCr15 bearing steel

This study investigates the effect of Al 2 O 3 content and the CaO/SiO 2 ratio in ladle furnace (LF) refining slag on the cleanliness of GCr15 bearing steel at 1600 °C through laboratory-scale thermal simulation experiments. Additionally, the influence of stirring during refining on the removal of single globular type inclusions by the slag was qualitatively evaluated. Large inclusion particles were nondestructively extracted from steel samples using anhydrous electrolysis. The morphology and chemical composition of these inclusions were analyzed via scanning electron microscopy (SEM). Using FactSage 8.4 software, variations in the low melting-point region of the CaO-Al 2 O 3 -SiO 2 -MgO slag system due to compositional changes were calculated. Results indicate that with a refining slag basicity of 4, the total oxygen content in the steel is minimized, and both the size and number density of group DS inclusions are reduced. Low-basicity slag effectively removes single globular type inclusions but exhibits limited capacity for removing other inclusion types. High-basicity slag has poor Al 2 O 3 removal capability and promotes the formation of numerous calcium-containing composite DS type inclusions. Increasing Al 2 O 3 content to 30% enhances slag fluidity, eliminating the need for CaF 2 addition, thereby reducing ladle lining erosion and environmental pollution. Furthermore, stirring during refining promotes collision and aggregation of fine inclusions, effectively reducing single globular type inclusions in the steel.