| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick steel plate exhibiting satisfactory HAZ toughness even if ultra high heat input welding of≥40 kJ/mm is performed, and further having excellent base metal toughness, elongation and strength-elongation balance. SOLUTION: The thick steel plate has a composition comprising 0.030 to 0.10% C,≤1.0% Si, 0.8 to 2.0% Mn,≤0.03% P,≤0.01% S, 0.01 to 0.10% Al, 0.005 to 0.035% Nb, 0.015 to 0.03% Ti, 0.0010 to 0.0035% B, 0.0050 to 0.01% N, 0 to 2.0% Cu, 0 to 2.0% Ni, 0 to 1% Cr, 0 to 0.5% Mo and 0 to 0.1% V, and in which the area ratio of retained austenite is 2 to 10% and the equivalent circle diameter of martensite-austenite constituent (MA) is≤3.0μm, and further having satisfying inequalities (1) and (2): 1.5≤[Ti]/[N]≤4 (1) and 40≤X value≤160 (2). COPYRIGHT: (C)2009,JPO&INPIT
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