Método de produção de chapa grossa de aço de alta resistência da classe de 780 mpa excelente em tenacidade a baixa temperatura

A method of production of 780 MPa class high strength steel plate excellent low temperature toughness comprising heating a steel slab of containing, by mass%, C: 0.06 to 0.15%, Si: 0.05 to 0.35%, Mn: 0.60 to 2.00%, P: 0.015% or less, S: 0.015% or less, Cu: 0.1 to 0.5%, Ni: 0.1 to 1.5%, Cr: 0.05 to 0.8%, Mo: 0.05 to 0.6%, Nb: less than 0.005%, V: 0.005 to 0.060%, Ti: less than 0.003%, Al: 0.02 to 0.10%, B: 0.0005 to 0.003%, and N: 0.002 to 0.006% to 1050°C to 1200°C in temperature, hot rolling ending at 870°C or more, waiting for 10 seconds to 90 seconds, then cooling from 840°C or more in temperature by a 5°C/s or more cooling rate to 200°C, then tempering at 450°C to 650°C in temperature for 20 minutes to 60 minutes.