| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength steel plate small in the variation of the material in the plate thickness direction and also excellent in strength, low temp. toughness and weldability. SOLUTION: A slab having a compsn. contg., by weight, 0.005 to 0.12% C, 0.02 to 0.5% Si, 0.3 to 2.2% Mn, <=0.02% P, <=0.01% S, 0.01 to 1% Mo, <=0.05% Al, 0.005 to 0.03% Ti, 0.0005 to 0.003% B and <=0.01% N, consisting of the balance iron with inevitable impurities and satisfying 0%<=Ti-3.4N<=0.02% is heated at 1000 to 1250 deg.C, is rolled in such a manner that the draft at <=950 deg.C is controlled to >=30%, and the finishing temp. is controlled to 700 to 850 deg.C, and, after that, cooling is executed at a cooling rate of 0.05 to 100 deg.C/sec to produce the steel plate. Preferably, it contains one or >= two kinds among Nb, Ni, Cr, Cu, V, Ca, Mg and rare earth metals.
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