| 摘要 |
PURPOSE:To produce an ultraclean steel suitable for a spring steel, bearing steel, by etc., by subjecting a molten steel to an ultralow oxygen treatment and ultralow TiN treatment on the outside of the furnace then adding Ca to the molten steel so that the oxide and nitride inclusions in the molten steel are made extremely little in amt. and small in size. CONSTITUTION:The molten steel is taken out of a refining furnace such as converter and is subjected to an RH degassing treatment to decrease the oxygen contained therein to <=15ppm content by the degassing treatment. Si, Mn, Ni, Cr, Mo, etc., contg. Ti at a low ratio are added as the raw material for steel making to the molten steel at the same instant and the molten steel is subjected to the RH degassing treatment; further the molten steel is bubbled by the gaseous Ar blown thereto to the ultralow Ti content of <50ppm Ti and <60ppm N. As the nonmetallic inclusions in the molten steel, the oxide inclusions are decreased in the disoxidation treatment by the RH degassing treatment and the nitride inclusions are decreased by the decrease of N; in addition, a Ca flux is blown into the molten steel to diminish the inclusions of <=25mum thickness and <20 score by a penalty point method at which the inclusions are easily deformed and crushed in the stage of hot rolling. The inclusions are thus made extremely small in quantity and size and the quality deterioration is prevented.
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