| 摘要 |
Provided are a high strength steel plate having excellent brittle crack arrestability and a method for manufacturing the same. A steel plate, which contains C, Si, Mn, Al, P, S and N each in a definite amount, satisfies the requirement Ceq (=C+Mn/6+(Cu+Ni)/15+(V+Mo+Cr)/5) being 0.34-0.49% inclusive, and may further contain, if required, one or more members selected from among Nb, Ti, Cu, Ni, Cr, Mo, V, Ca, B and REM, wherein a region with an aggregate tissue, said region having an X-ray diffraction intensity ratio according to plane (211) in a plane parallel to the surface of the steel plate of 1.0 or greater, is disposed within at least 1/3 of the sheet thickness including the central part of the sheet thickness, the bainite fraction at the central part of the sheet thickness is 80% or greater, and the Charpy fracture transition temperature at a position of 1/4 of the sheet thickness is -40°C or lower. The method according to the present invention comprises hot rolling a steel material in such a manner that the cumulative rolling reduction ratio is at least 50% within a temperature range at the central part of the sheet thickness from (Ar3+60)°C to Ar3 inclusive, and then cooling to 450°C or lower at a cooling speed of 4.0°C/s or higher. |
