| 简介 |
PROBLEM TO BE SOLVED : To provide a high strength thick steel plate with a plate thickness of >50 mm having excellent brittle crack arrest properties and used for a large-sized structure such as a vessel, and to provide its production method.
SOLUTION : The steel plate has a texture where the X-ray intensity ratio in the (111) plane at the rolling face in the central part of the plate thickness is ≥2.0, the X-ray intensity ratio in the (110) plane at the rolling face in the plate thickness of 1/4 is ≥1.5, and also, the X-ray intensity ratio in the (100) plane at the rolling face in the surface layer of the plate thickness is ≥2.0, and has a steel composition comprising, by prescribed mass%, C, Si, Mn, Al, P, S and N, and, if required, further comprising one or more kinds selected from Ti, Nb, Cu, Ni, Cr, Mo, V, B, Ca and rare earth metals. Regarding the production method, the steel having the above composition is heated at 900 to 1, 200°C, is subjected to rolling in such a manner that the friction coefficient between a work roll and the plate in the hot rolling is controlled to ≥0.20, the cumulative draft at an Ar3 point or above in the central part of the plate thickness is controlled to ≥30%, and the cumulative draft in the temperature range of an (Ar3 point)-40°C or below to an (Ar3 point)-100°C or above is controlled to ≥30%, and is thereafter cooled to ≤600°C at a cooling rate of ≥2°C/s.
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