| 摘要 |
PURPOSE:To produce an extra-low-carbon steel having excellent quality at a low cost by providing a secondary decarburization refining stage consisting of blowing of an inert gas and surface oxygen blowing of the crude molten steel in a ladle between decarburization refining and vacuum degassing treatment in a converter. CONSTITUTION:A molten iron is subjected to decarburization refining in a top and bottom blown converter by the conventional method and the crude molten steel having about 0.03-0.05% carbon content is tapped into the ladle. An immersion pipe is inserted into such crude molten steel and an inert gas such as gaseous Ar is blown into the ladle from the bottom thereof to stir the crude molten steel; at the same time an oxidative gas is blown onto the surface of the crude molten steel in the immersion pipe to execute secondary decarburization. The molten steel which is decreased in the carbon content to about 0.01% by such secondary decarburization is subjected to the vacuum degassing treatment by the conventional method to decrease the carbon content to about <=20ppm. The treatment time is thereby reduced and the extra-low- carbon steel having the good quality is produced. |
