| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a high-strength extra-thick steel plate, which is made from a cast slab continuously cast using an existing rolling mill for a thick plate, which shows no defect in an ultrasonic flaw detection test, and which excels in inner quality. SOLUTION: A slab is cast in such a way that its width central part including an unsolidified part is subjected to rolling-reduction by 3-15 mm with a pair of reduction rolls while the solid-phase ratio of its thickness central part is in a range of≥0.8 and <1.0. An extra-thick steel plate is obtained by hot-rolling the cast slab as a material under the condition that the reduction ratio r until a finish rolling is 1.5-4.0. The level of a tensile strength X of the extra-thick steel plate is a 400-600 MPa class. A central porosity volume Vp of the thickness central part of the extra-thick steel plate satisfies the relation: Vp<Vp<SB>0</SB>/r, wherein Vp<SB>0</SB>is a converted central porosity volume calculated from the tensile strength of the extra-thick steel plate. COPYRIGHT: (C)2007,JPO&INPIT
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