| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength thick steel plate having superior HAZ toughness even when having been welded at such a high heat input as an amount of 30 to 100 kJ/mm or more. SOLUTION: This thick steel plate satisfies a predetermined chemical component composition, and has a BP value in a range of 90 to 200 (mass%), which is specified by the following expression (1): BP value (mass%)=414[C]+78[Si]+31[Mn]+79[Cr]-14[Cu]-26[Ni]+218[Mo], wherein [C], [Si], [Mn], [Cr], [Cu], [Ni] and [Mo] represent contents (mass%) of C, Si, Mn, Cr, Cu, Ni and Mo respectively. Furthermore, 5.0×10<SP>6</SP>pieces or more per 1 mm<SP>2</SP>of Ti-containing nitrides having circle equivalent diameters of 0.05μm or smaller exist in the thick steel plate, and among them, the number of the Ti-containing nitrides having circle equivalent diameters of 0.01 to 0.03μm is 75% or more of the total number of the Ti-containing nitrides. COPYRIGHT: (C)2009,JPO&INPIT
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