| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength thick steel sheet with a sheet thickness of at least 50 mm excellent in brittle crack arrestability and a method for producing the same.SOLUTION: The thick steel sheet has texture where the intensity in the {100}<011> orientation in the rolled face in the central part of the sheet thickness is 2.0 or more, and the intensity in the {100}<011> orientation in the rolled face in the 1/4 part of the sheet thickness is 1.2 or more; has a Charpy fracture transition temperature of -40°C or less in the 1/4 part of the sheet thickness; and has steel composition containing, by mass%, 0.03-0.20% of C, 0.03-0.5% of Si, 0.5-2.2% of Mn, 0.005-0.08% of Al, 0.03% or less of P, 0.01% or less of S, 0.0075% or less of N, and at least one or two or more of Ti, Nb, Cu, Ni, Cr, Mo, V, B, Ca, and REM. The steel of the composition is heated to a temperature of 900-1,200°C, subjected to rolling using a lubricant, in which cumulative rolling reduction is at least 30% at a temperature at which the central part of the sheet thickness is a recrystallized γ region, and the cumulative rolling reduction is at least 50% in a temperature region in which the central part of the sheet thickness is an unrecrystallized γ region, and then cooled to 600°C or less at a cooling rate of 2°C/s or more, or tempering is performed at an Ac1 point or less after the accelerated cooling. |
