Method of vacuum decarburization/refining of molten steel

A method for vacuum decarburization refining of a molten steel comprising:

• providing molten steel having a carbon concentration of 1.0 to 0.01% by weight in a ladle;
• providing a vacuum tank having a one-legged, straight barrel snorkel as a lower portion of said vacuum tank;
• immersing said one-legged, straight barrel snorkel of said vacuum tank into said molten steel in said ladle;
• evacuating an interior of said vacuum tank resulting in molten steel ascending in an interior of said one-legged, straight barrel snorkel immersed in said molten steel and into said interior of said vacuum tank;
• providing a liftable top-blown lance in an insert hole in a canopy of said vacuum tank;
• blowing oxygen gas through said top-blown lance into said molten steel at a flow rate in a range of 3 to 25 Nm2/hr/ton-steel;
• injecting inert gas into said molten steel from a low position of said ladle at a flow rate in a range of from 0.3 to 10 Nl/min/ton-steel;
• regulating a degree of vacuum in said vacuum tank at a high carbon concentration region, said carbon concentration of said molten steel in said high carbon concentration region being not less than a critical carbon concentration, said critical carbon concentration being in a range of 0.3 to 0.1% by weight;
• said degree of vacuum at said high carbon concentration region being regulated 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)
• P<760
• wherein T represents molten steel temperature, K, and P represents the degree of vacuum in the vacuum tank, Torr;
• thereby conducting oxygen blowing decarburization refining, followed by degassing.