Effect of the Al₂O₃ Content in the Slag on the Remelting Behavior of a Bearing Steel

The service life of roller bearings strongly depends on nonmetallic inclusions (NMIs). Therefore, these steels request highest metallurgical standards in their production. To determine the effect of the Al₂O₃ content and a protective atmosphere (N₂) on the electroslag remelting (ESR) behavior, laboratory scale experiments are conducted. Changes in the composition of the remelted materials and in the slag are determined. In addition, the amount and composition of the NMI prior and after remelting are investigated, and thermodynamic simulations on the formation of NMI are conducted. Changes in the chemical composition can largely be explained by well-known equilibrium reactions between the slag and the metal. Lowest Al contents in the remelted steel can only be achieved with the Al₂O₃-free slag. Higher Al₂O₃ contents in the slag lead to higher oxygen and sulfur contents in the steel and corresponding higher amounts of NMI after remelting. The use of a protective gas mainly reduced the loss of Si and led to lower O and S contents after remelting with the Al₂O₃-free slag. The composition of the NMI changed from alumina type to MgO–Al₂O₃ (MA)-spinel type and finally mixed MgO–SiO₂ oxides with decreasing Al₂O₃ contents. These results are confirmed by thermodynamic calculations.