In the production mannered null molten steel of the thick meat high tension steel sheet which is superior in super full house thermal welding

摘要

PROBLEM TO BE SOLVED: To provide a method of producing a thick high tensile strength steel plate which has excellent toughness in a heat affected zone by ultrahigh heat input welding in a heat input of 300 kJ/cm.;SOLUTION: Si and/or Mn is added to molten steel, and is deoxidized to control the content of dissolved oxygen to 0.0030 to 0.0120 mass%. After that, rare earth metals are added thereto to control the dissolved oxygen content to 0.0010 to 0.0050 mass%. Further, the molten steel is made into the one having a composition in which the contents of C, Si, Mn and P are controlled to the proper ranges as well, and containing 0.0005 to 0.0060% S and 0.0030 to 0.0200% rare earth metals, and the contents of Al and Ti are limited to ≤0.004%, respectively. The molten steel is then cast into a steel stock. The steel stock is thereafter heated at 1,050 to 1,200°C, subsequently subjected to hot rolling where the cumulative draft in the temperature range of Ar₃ to (Ar₃+100°C) is ≥35%. Next, cooling at a mean cooling rate of ≥2°C/s is applied to the temperature range of ≤450°C. One or more kinds of metals selected from Nb, V, Cu, Ni, Cr, Mo and B can further be contained in addition to the above composition.;COPYRIGHT: (C)2004,JPO