PROCESS FOR PRODUCING INGOT OF ULTRALOW-SULFUR HIGH-CLEANLINESS STEEL

摘要

An ultralow-sulfur high-cleanliness steel having an [S] of 10 ppm or lower and a T.[O] of 40 ppm or lower is produced by a simple means without the need of adding CaF<SUB>2</SUB> to a molten steel in a ladle or increasing the temperature of the steel being discharged from a converter. The following steps are successively conducted: a step (1) in which a CaO flux is added to a molten steel in a ladle at atmospheric pressure; a step (2) in which a stirring gas is bubbled into this molten steel in the ladle at atmospheric pressure through a lance immersed in the molten steel to thereby stir the molten steel and the CaO flux, and an oxidizing gas is supplied to the molten steel in the ladle to thereby react the oxidizing gas with the molten steel in the ladle and mixing the resultant oxides with the CaO flux; and a step (3) in which the supply of the oxidizing gas is stopped, and the stirring gas is bubbled into the molten steel in the ladle at atmospheric pressure through the lance immersed in the molten steel to thereby conduct desulfurization and inclusion removal. In this operation, the ratio of the stirring time (t) in step (3) to the oxidizing-gas supply time (t<SUB>0</SUB>) in step (2), (t/t<SUB>0</SUB>), is regulated to 0.6 or higher.