PURPOSE: To decrease internal segregation and shrinkable defects and to cast a steel having good internal quality by insulating the heat of the top surface of a molten steel having a specific depth or below and allowing the mooten steel to solidify positively from the bottom surface so as to execute substantially unidirectional solidification from the bottom surface toward the top surface.
CONSTITUTION: The molten steel 4 poured into a casting mold 3 lined internally with the heat insulating material 2 on an ingot mold stool 1 is cooled only from the top surface and bottom surface or from the bottom surface and is allowed to solidify positively from the bottom surface of the steel 4 in a vertically short steel ingot method consisting in pouring the molten steel 4 into the above-mentioned casting mold so as to form an ingot having ≤400mm thickness. After the solidified steel from the top surface is formed to ≤30mm thickness, the solidified layer 5 formed first is insulated by a heat insulating material 6. The substantially unidirectional solidification from the bottom toward the top surface is thus executed in such a manner that the finally solidified part 7 exists adjacently to the layer 5. The internal quality is hereby improved and the need for grinding the surface layer part of the steel material after casting is eliminated. The ingot is thus easily cast at a high yield.
MARUKAWA YUJO
KASAI NOBUFUMI
OKAMOTO SETSUO
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