Abstract: In a process for vacuum refining a molten steel wherein a refining flux is used, a fuel gas and an oxygen gas are spouted into the outlet of a top-blown lance of a vacuum refining apparatus to form a burner flame below the top-blown lance, and, at the same time, a refining flux is fed into the top-blown lance with the aid of an oxygen gas as a carrier gas and further passed through the burner flame, and the heated and melted refining flux is allowed to arrive at the surface of the molten steel. In this case, the refining flux feed rate and the circulating flow rate of the molten steel during vacuum refining are regulated so as to have a predetermined relationship, achieving a low flux consumption throughout a period of single refractory life of the vacuum tank.

Abstract: Molten steel is efficiently vacuum treated in a vacuum treatment vessel provided with a top blow lance capable of injecting oxygen and a gaseous fuel at desired flow rates, respectively, into the molten steel. The blow lance is provided on the top of the vacuum treatment vessel and is supported so as to be freely vertically movable. By spacing the lower end of the top blow lance not more than 2 m from the surface of the molten steel bath and injecting only oxygen onto the molten steel, and spacing the lower end of the top blow lance 1.0 m or more from the surface of the molten steel bath and injecting both oxygen and a gaseous fuel gas onto the molten steel, the temperature of the molten steel is prevented from decreasing during the vacuum treatment and the molten steel is so prevented from depositing on the inside wall of the vacuum treatment vessel.