Comparison Study of the Effect of MgO, MgO-CaO, MgO-Al2O3-C, and MgO-C Refractories on Cleanliness of a SiMn-Killed Steel

The effects of four kinds of industrial MgO-based refractories (MgO, MgO-CaO, MgO-Al₂O₃-C, and MgO-C) on the refractory/steel interfacial layer and inclusions in SiMn-killed steel are investigated through laboratory experiments and thermodynamic calculations. After 60 min of contact, the penetration of the molten SiMn-killed steel into the MgO, MgO-CaO, and MgO-Al₂O₃-C refractories is minimal. In the MgO-C refractory, a penetration depth of 1 mm is observed along grain boundaries. For MgO and MgO-C refractories, a distinct interfacial layer is hardly found. The MgO-CaO refractory produces an ≈20 μm thick CaO-SiO₂-MgO interfacial layer, while the MgO-Al₂O₃-C refractory produces an ≈30 μm thick MgO-Al₂O₃-SiO₂ interfacial layer. Regarding the experiments involving the MgO and MgO-CaO refractories, the content of T.Mg and T.Al in the steel shows minimal variation. Consequently, the composition of inclusions remains largely unchanged. MgO-Al₂O₃-C and MgO-C refractories significantly influenced the chemical reaction. The T.Mg content in the steel increases due to the presence of graphite phase in the refractory, and the T.Al content in the steel rises due to the dissolution of Al and Al₂O₃ particles from the refractories. Inclusions in the steel are transformed from the initial SiO₂-MnO type to spinel inclusions.