METHOD OF PRODUCING HIGH TENSILE STRENGTH THICK STEEL PLATE HAVING EXCELLENT WELDABILITY AND LOW TEM

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PROBLEM TO BE SOLVED : To provide a method of producing a high tensile strength thick steel plate having excellent weldability and low temperature toughness. SOLUTION : A steel stock having a composition comprising 0.003 to 0.060% C, ≤0.6% Si, 1.0 to 3.0% Mn, 0.005 to 0.10% Al, 0.0003 to 0.0050% B and 0.005 to 0.050% Ti, and further comprising one or more kinds of metals selected from 0.015 to 0.20% Nb and 0.15 to 1.0% Mo is heated at 950 to 1, 200°C, and is thereafter subjected to hot rolling including cross rolling in the temperature range of ≤950°C for one or more passes, and in which rolling finishing temperature is ≥700°C. Regarding the cross rolling, the cross angle [!theta!] is controlled to ≥20°, and in the rolling pass at ≤950°C, the cumulative rolling strain defined by Σi{ln(Ai/Bi)×sin[!theta!]i} is controlled to ≥0.25. Thus, the thick steel plate having excellent weldability and low temperature toughness can be obtained. It is preferable that, after the completion of the hot rolling, accelerated cooling is performed to ≤580°C at a cooling rate of ≥7°C/s, and also, tempering is performed in the temperature range of 500 to 650°C. The steel plate may comprise V, Cu, Ni, Cr, W, Ca and rare earth metals as well.