| 摘要 |
<p>A thick steel plate which simultaneously increases the minimum toughness and improves an average toughness value in the proximity of a bond of heat affected zone and maintains a good toughness balance in the proximity of the bond is provided, and a thick steel plate having excellent toughness in welding heat affected zone and excellent toughness of base metals themselves at the same time although high heat input welding has been performed on the thick steel plate is provided. A thick steel plate having excellent toughness in welding heat affected zone comprises, by mass percent, 0.03 to 0.12% of C, 0.2% or less(including 0%) of Si, 1.0 to 2.0% of Mn, 0.03% or less(excluding 0%) of P, 0.015% or less(excluding 0%) of S, 0.10% or less(excluding 0%) of Al, 0.015 to 0.08% of Ti, 0.0060 to 0.0120% of N, 0.0010 to 0.0050% of B, and 0.005 to 0.020% of Nb and/or 0.0001 to 0.050% of Zr, the thick steel plate satisfies the relational expression of [Ti]x16[Si]x(12-40[C])<0.38(%), where [Ti], [Si] and [C] denote contents(mass%) of Ti, Si and C respectively, and Ti-containing nitrides with an equivalent circle diameter of not greater than 0.05 mum are present in the thick steel plate in the number of not less than 5.0x10^6 per 1 mm^2 of the thick steel plate.</p> |
