METHOD OF PRODUCING THICK HIGH TENSILE STRENGTH STEEL PLATE HAVING EXCELLENT TOUGHNESS IN HEAT AFFECTED ZONE BY ULTRAHIGH HEAT INPUT 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 Ar3to (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