Impact of magnesium oxide content on the structure and viscous flow properties of GCr15-bearing steel refining slag

The presence of MgO is crucial in refining slags used for bearing steel . However, the relationship between the viscous behavior of slag and its structural characteristics is not yet fully understood. In this study, we prepared high-basicity CaO-SiO 2 -Al 2 O 3 -CaF 2 +MgO (0–9%) refining slag systems and assessed the influence of MgO on viscous behavior and structural characteristics. The results demonstrate that MgO has a pronounced effect on the slag system, notably lowering the melting point and altering its viscosity . The viscous behavior of each slag system followed an Arrhenius behavior within 1450–1480 °C and 1505–1600 °C. However, between 1480 and 1505 °C, a significant deviation from Arrhenius's behavior was observed. The activation energy for the viscous flow ( E η ) of the MgO-containing slag exceeded 84 kJ/mol in the range of 1505–1600 °C, which was 10 kJ/mol greater than that in the range of 1450–1480 °C. Infrared and Raman spectroscopy analyses revealed that the structural characteristics and viscous behaviors of slags were governed primarily by the polymerization‒depolymerization of the i (Si/Ca/Mg/Al)-BO/NBO- j (Si/Ca/Mg/Al) polymer structure , which was only slightly affected by the [SiO] units with bridging oxygen. The formation of microcrystalline phases suggests that the slag structure consists of complex aluminum–silicate oxygen polymers interspersed with microcrystalline phases. As the MgO content increased, the sequence of generated microcrystalline phases was as follows: calcium aluminate silicate → olivine → spinel → calcium magnesium silicate. These structural features collectively potentially led to the low viscosity and high structural sensitivity of the slag, and when the MgO content ranged from 5 % to 7 %, the comprehensive performance of the refined slag was optimal. This research offers new insights into slag optimization and the formation and evolution of inclusions in steel.