| 摘要 |
When molten steel is poured using an immersion nozzle in a state in which a direct current magnetic field zone is applied to a cast slab over the entire width in the thickness direction thereof at a position a predetermined distance below the molten metal level in a continuously-casting mold, the immersion nozzle is provided with ejection holes located in at least upper and lower two stages, at least one lower ejection hole is disposed such that these satisfies the following formula (1), the supply rate of the molten steel from upper ejection holes is set smaller than the rate consumed by solidification in an upper pool, and a particular solute element is added to the molten steel in the upper pool.<paragraph lvl="0"><in-line-formula>0<h<(½).w.tan theta (1)</in-line-formula>where, theta: downward angle of lower ejection hole(s) (°); w: length of mold in width direction (m); and h: distance from center of lower ejection hole to center of height of magnetic pole (m) With this arrangement, not only the supply of molten steel to the upper and lower pools, in which the concentration of the solute element is different on both the sides of the direct current magnetic field zone acting as a boundary, can be controlled very easily but also a multi-layer cast slab, in which the dispersion of concentration of the solute element is very small in the surface layer portion of the cast slab, can be stably manufactured.
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