| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength thick steel plate having excellent toughness of weld heat-affected zone (HAZ) in ultrahigh heat input welding employing a heat input exceeding 400 kJ/cm and also to provide its manufacturing method. SOLUTION: The high strength thick steel plate with excellent toughness of HAZ in ultrahigh heat input welding can be manufactured by adding Si and/or Mn to molten steel to carry out deoxidation and regulate dissolved oxygen content to 0.0030 to 0.0120 mass%, then adding REM to prepare molten steel which contains 0.001 to <0.030% C, 0.05-0.40% Si, 0.5-2.0% Mn,≤0.03% P, 0.0005-0.0060% S, 0.0005-0.0050% REM, 0.0003-0.0060% B and further either or both of 0.010-0.070% Nb and 0.1-0.8% Mo and in which Al and Ti are limited each to≤0.004%, casting the molten steel and then applying hot rolling to the resultant steel stock to form the thick steel plate. This high strength thick steel plate has a structure in which grains of the sulfide, oxide and oxysulfide of REM having≤10μm average grain size and grains of the oxide, sulfide and oxysulfide of Mn having≤1μm average grain size are dispersed. COPYRIGHT: (C)2004,JPO
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