| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength thick steel plate having ≥50 mm plate thickness, excellent in brittleness-cracking propagation-stopping characteristic and method for manufacturing the same.SOLUTION: The thick steel plate has a texture, in which {100}<011> directional strength on the rolled surface in the center part of the plate thickness is ≥2.0 and {100}<011> directional strength on the rolled surface in the 1/4 part of the plate thickness is ≥1.2, and has -40°C or lower of Charpy fracture transition temperature in the 1/4 part of the plate thickness, and has the steel composition composed by mass of 0.03-0.20% C, 0.03-0.5% Si, 0.5-2.2% Mn, 0.005-0.08% Al, ≤0.03% P, ≤0.01% S, ≤0.0075% N and one or more elements among Ti, Nb, Cu, Ni, Cr, Mo, V, B, Ca, REM. The steel having the composition, is heated to 900-1,200°C temperature and is rolled into ≥30% cumulative rolling-reduction ratio in the temperature-zone becoming recrystal γ-zone at the center part of the plate-thickness and into ≥50% cumulative rolling-reduction ratio in the temperature zone becoming α+γ zone at the center part of the plate thickness by using lubricant and thereafter, is cooled to 600°C or lower at ≥2°C/s cooling rate, or after the accelerated-cooling, tempering is performed at Acpoint temperature or lower. |
