| 摘要 |
A high-strength thick steel plate having a composition of Ni-containing steel and bainite-dominated structure, wherein a pearlite fraction is not greater than 5%, fraction of coarse ferrite having a circle equivalent diameter of larger than 25 µm is not greater than 10% in front and back surface portions each having a depth of 5% of the plate thickness, mean circle equivalent diameter of cementite is not greater than 0.5µm, and mean circle equivalent diameter of iso-crack propagation resisting domains is not greater than d (µm)=(7.1 ×[Ni]+11) ×(1.2-t/300) (µm), where each of the iso-crack propagation resisting domains is defined such that inner portion excluding the surface portions in a section perpendicular to the rolling direction of the steel plate is partitioned to iso-orientation domains, the measuring line of cutting method is drawn along T direction in parallel to the plate thickness, the plural iso-orientation domains continuously aligned and adjacent to each other are identified excluding iso-orientation domains having a circle equivalent diameter of smaller than 8µm, the angle between <001> axes close to the T direction of each pair of the identified iso-orientation domains is measured, and the continuously aligned iso-orientation domains satisfying the angle of not greater than 20° are regarded to constitute one iso-crack propagation resisting domain. |
