Converter steelmaking method
A method of producing molten steel supplies gaseous oxygen from a top blowing lance into a converter to perform decarburization refining of molten iron while adding a CaO-containing powdery dephosphorizing agent to simultaneously decarburize and dephosphorize the molten iron and includes supplying the dephosphorizing agent to a bath surface of the molten iron together with at least one gas jet from the top blowing lance and a dynamic pressure determined when a gas jet blown from respective lance nozzles of the top blowing lance impinges onto the bath surface of the molten iron is controlled to not more than 0.50 kgf/cm 2 .
1. A converter steelmaking method of producing molten steel by supplying gaseous oxygen from a top blowing lance into a converter to perform decarburization refining of molten iron while adding a CaO-containing powdery dephosphorizing agent to simultaneously decarburize and dephosphorize the molten iron, comprising:
joining the dephosphorizing agent and the gaseous oxygen together in the same lance;
supplying the dephosphorizing agent to a bath surface of the molten iron together with at least one gas jet from the top blowing lance; and
controlling a dynamic pressure determined from formulae (1)-(4) including an increasing amount of dynamic pressure due to a kinetic energy of the dephosphorizing agent when a gas jet including the gaseous oxygen accompanied by the dephosphorizing agent blown from respective lance nozzles of the top blowing lance impinges onto the bath surface of the molten iron to be not less than 0.10 kgf/cm 2 and not more than 0.50 kgf/cm 2 :
P= 3.13×10 −11 ×ρg ×( U 0 ×de×P 0 /Lh ) 2 (1)
U 0 =740(1−(1.033 /P 0 ) 2/7 ) 1/2 (2)
P 0 =Fj /(0.456 ×dt 2 ) (3)
ρ g=ρj+Vp /( Fj/ 60) (4),
wherein
P: dynamic pressure at a center of the jet exerted on the bath surface of the molten iron by the gas jet blown from the lance nozzle [kgf/cm 2 ]
ρg: density of the gas jet [kg/Nm 3 ]
U 0 : velocity of the gas jet blown from the lance nozzle [m/sec]
de: outlet diameter of the lance nozzle [mm]
P 0 : pressure at nozzle inlet of the gas blown from the lance nozzle [kgf/cm 2 ]
Lh: lance height [m]
Fj: supply rate of the gas blown from the lance nozzle [Nm 3 /hr]
dt: throat diameter of the lance nozzle [mm]
ρj: density of the gas blown from the lance nozzle [kg/Nm 3 ]
Vp: supply rate of the powdery dephosphorizing agent [kg/min].
2. The converter steelmaking method according to claim 1 , wherein a dynamic pressure determined from formulae (1)-(4) when the gas jet including the gaseous oxygen accompanied by the dephosphorizing agent, which is blown from respective lance nozzles of the top blowing lance, is impinging onto the bath surface of the molten iron is controlled to not more than 0.30 kgf/cm 2 .
3. The converter steelmaking method according to claim 1 , wherein the dephosphorizing agent is one or more selected from quicklime, hydrated lime, calcium carbonate, converter slag and ladle slag, each having a particle size of not more than 1 mm.