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The effect of calcium addition on inclusions (oxides and sulfides) in heavy steel ingot is investigated via lab experiments and thermodynamic calculation. The characteristics (chemistry, size, morphology, and number) of inclusions in the steel samples are investigated by scanning electron microscope with an energy‐dispersive spectrometer. The three‐dimensional morphology of inclusions is investigated by the nonaqueous solution electrolysis method. Inclusions in the fast‐quenched steel are changed from Al2O3 to Al2O3–CaO, Al2O3–CaO–CaS, and CaS after Ca addition. After slow cooling, inclusions in the solid steels are changed from Al2O3, single MnS, and Al2O3–MnS complex inclusions to Al2O3–CaO–CaS–MnS and CaS–MnS. The evolution trajectory of inclusions is Al2O3→Al2O3–CaO→Al2O3–CaO–CaS→Al2O3–CaO–CaS–MnS. With increasing Ca content in the steel, the number density and proportion of single MnS inclusions decrease. The formation mechanism of inclusions after Ca addition is explained by thermodynamic calculation. [ABSTRACT FROM AUTHOR]

Laboratory experiments are performed to study the effect of T.Ca content in the molten steel on the composition, size, and quantity of inclusions. Different amounts of SiCa alloys are added into the molten steel to obtain samples with varied T.Ca contents. Samples are taken at 1, 5, 10, 15, and 20 min after the calcium addition to study the transformation of inclusions with time. After the addition of calcium into the molten steel, the size of pure liquid inclusions is small which are more difficult to be removed from the molten steel than solid ones, while partially liquid inclusions are easily removed from the molten steel so that the total oxygen content of the molten steel is lower. The size of solid inclusions is large due to their large coagulation coefficient value. The number density and area fraction of liquid inclusions are larger than solid inclusions due to the higher adhesion work required for the removal of liquid inclusions. The corrosion of MgO crucible easily occurs by the dissolved calcium in the molten steel. Then, the reaction between the reduced magnesium and inclusions in the molten can occur, leading to the generation of MgO–Al2O3 and CaO–MgO–Al2O3 inclusions. [ABSTRACT FROM AUTHOR]