| 摘要 |
PROBLEM TO BE SOLVED: To suppress an increase in a bubble defect, even when a flow rate of Ar gas flowing to an inner surface of an immersion nozzle is increased.SOLUTION: When the flow rate of Ar gas of blowing to a position upstream of a flow passage orifice of a clearance of a sliding gate 5 forming the flow passage orifice for adjusting the flow rate or a clearance between a stopper 13 and an upper nozzle 9, the flow rate of the Ar gas blowing to a position downstream of the flow passage orifice and the inner area of the immersion nozzle are denoted by q(N liter/min), q(N liter/min) and A(m), respectively, high purity Ar gas having a purity of 99.95 vol% or more, an oxygen concentration of 2 volppm or less and a dew point of -65°C or lees, is flowed to the inner surface of the immersion nozzle so that a value of {(q/5)+q}/A becomes between 3-25. Since an increase in the bubble defect can be suppressed even when the flow rate of the Ar gas flowing to the inner surface of the immersion nozzle is increased, the occurrence of a surface bubble defect can be effectively prevented even when an extra-low-carbon steel slab meeting a high quality requirement level is produced. |
