TW369566B - Vacuum decarburization refining method for molten steel and apparatus thereof - Google Patents

Abstract

The present invention relates to a molten metal decarburizing method which is carried out by using a straight barrel type vacuum refining apparatus, in which an oxygen flow rate and an inert gas flow rate are controlled and a blowing oxygen gas flow rate is reduced at a reducing speed of 0.5 to 12.5 Nm<SP>3</SP>/h/ton/min in a low carbon concentration region less than the critical carbon concentration; and moreover, a molten steel refining method in which, in an Al heating process which Al added into the vacuum vessel is burned, an atmosphere in a vacuum vessel is controlled in such a way that G which is obtained according to the following equation (1): G=5.96x10<SP>-3</SP>xTxIn (P/Pco), may be a value of -20 or less and in a process of decarburization refining, in a high carbon concentration region higher than the critical carbon concentration, the above atmosphere is controlled in such a way that G may be in a range of -35 to -20, and the molten steel is decarburized; conditioning a slag; conditions of blowing an inert gas from a ladle bottom, in the duration of blowing oxygen for decarburization, in the duration of carrying out degassing treatment and in the duration of reducing the molten steel by burning Al; or the vacuum refining apparatus having means for retarding the accumulation of dusts; at least one of the above elements can be combined to the above molten metal decarburizing method. In which Pco=760x10<SP>(-13800/T+8.75)</SP>x[%C]/[%Cr] P < 760, where T is a molten steel temperature (K), and P is a vacuum pressure in a vacuum vessel (Ton).