| 摘要 |
<p>PURPOSE: A thick steel plate having excellent HAZ toughness is provided to properly control chemical components and structure and define average density in specific atom aggregate measured by a 3D atom probe electric field ion microscope. CONSTITUTION: A thick steel plate having excellent HAZ toughness comprises C of 0.01-0.10weight%, Si of 0.05weight% or less(0 is exclusive), Mn of 1.0-2.0weight%, P of 0.030weight% or less(0 is exclusive), S of 0.015weight% or less(0 is exclusive), Al of 0.005-0.070weight%, Nb of 0.003-0.030weight%, Ti of 0.005-0.05weight%, N of 0.0020-0.010weight%, B of 0.0006-0.0050weight%, Ca of 0.0005-0.008weight%, and iron and inevitable impurities of the remaining amount, where KV obtained by the following equation, KV=[V]+[Nb], is 0.060 or less. When measuring aggregate comprising the total five or more of Nb or C atoms in the thick steel plate using a 3D atom probe electric field ion microscope, the density of the aggregate is 1.0×10^22/m^3 or greater. [Reference numerals] (AA) Sphere with the radius of 1.7cm</p> |
