| 摘要 |
PROBLEM TO BE SOLVED: To suggest a thick steel plate showing an excellent toughness at heat affected zone in an extra-large heat input welding performed with a heat input of >300 kJ/cm, and its manufacturing process. SOLUTION: The thick steel plate is obtained by hot rolling a steel obtained by casting a molten steel comprising 0.03-0.18% C, 0.05-0.40% Si, 0.5-3.0% Mn,≤0.03 P, 0.0005-0.0060% S, 0.0030-0.0200% REM,≤0.0070% O,≤0.004% Al and≤0.004% Ti which is obtained by adding Si and/or Mn to a molten steel and deoxidizing it, adjusting an amount of dissolved oxygen to 0.0030-0.0120% and adding REM. This provides a metallic structure wherein particles of a sulfide, an oxide and an oxysulfide of REM with average particle sizes of≤10μm and particles of an oxide, a sulfide and an oxysulfide of Mn with average particle sizes of≤1μm are dispersed. In order to further improve the toughness of the heat affected zone, the addition of REM may be conducted using an REM-diluted alloy or an REM-containing mixture containing 40-70 mass% REM. COPYRIGHT: (C)2004,JPO
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