| 摘要 |
PROBLEM TO BE SOLVED: To stably produce a duplex-layer cast slab in which the supplying control of molten steel into the upper and the lower pool parts having different solute element concentrations with DC magnetic field zone as the boundary, is extremely easy and also, the foundation of the solute element concentration on the surface layer part of the cast slab is quite small. SOLUTION: When the molten steel is poured by using an immersion nozzle in the state of impressing the DC magnetic field zone over the whole width of the cast slab in the thickness direction of the cast slab at a fixed lower position from the molten steel surface level in a continuous casting mold, at least two spouting holes in the upper and the lower parts are arranged in the immersion nozzle. Further, the lower part spouting hole is disposed so as to satisfy the following inequality (1) and the supplying speed of the molten steel from the upper part spouting hole is smaller than the solidification speed in the upper pool part and also, a specified solute element is added to the molten steel at the upper pool part. 0<h<(1/2).w.tanθ...(1), wherein,θ: the downward angle ( deg.) of the lower spouting hole, w: the length (m) in the width direction of the mold and h: the distance (m) from the lower spouting hole center to the height center of a magnetic pole.
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