Abstract: In a straight barrel type vacuum refining apparatus, use is made of a combination of: a decarburization method wherein the flow rate of oxygen fed into a vacuum tank and the flow rate of an inert gas fed into the vacuum tank are regulated and, at the same time, the flow rate of oxygen gas blown is reduced at a rate of 0.5 to 12.5 Nm3/h/t/min in a low carbon concentration region having a carbon concentration of not more than the critical carbon concentration; and a vacuum refining apparatus provided with dust accumulation preventing means.

Abstract: A method for vacuum decarburization refining of a molten steel includes providing a vacuum tank having a one-legged, straight barrel snorkel as a lower portion of the vacuum tank. The a degree of vacuum in the vacuum tank is regulated at a high carbon concentration region to a value in a range of −35 to −20 in terms of G defined by the following equation (1): G=5.96×10−3×T×ln(P/Pco)  (1), wherein Pco=760{10(−13800/T+8.75)}×(% C)/(% Cr)  (2), and wherein P<760, T represents molten steel temperature, K, and P represents the degree of vacuum in the vacuum tank, Torr.