Abstract
This study investigated the effects of refractories (MgO vs. Al2O3) on the cleanliness and inclusion evolution in Al-killed steel during refining with a CaO-Al2O3-SiO2 slag (56.9% CaO, 35.0% Al2O3, 8.1% SiO2), combining laboratory experiments with thermodynamic calculations. The results show that with MgO crucibles, total oxygen and sulphur contents in steel remained low (6–8 and 4–5 ppm), and inclusions were CaO-Al2O3-MgO and MgO·Al2O3-based; area fraction and average size decreased with refining time. With Al2O3 crucibles, total oxygen and sulphur contents increased to 13–16 and 30–46 ppm, respectively, and sulphur reversion occurred. Inclusions were CaO-Al2O3-SiO2 and Al2O3-based, reaching minimum area fractions after 60 min of refining. Thermodynamic calculations revealed that the dissolution of MgO crucibles enhanced the slag's absorption capacity for CaO·2Al2O3 inclusions, while inhibiting the absorption of MgO and MgO·Al2O3 inclusions. Conversely, Al2O3 crucible dissolution weakened the slag's absorption capacity for calcium aluminate, MgO·Al2O3, and Al2O3 inclusions.
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