| 摘要 |
A process for the production of 780PMa-grade high-tensile -strength steel plates excellent in low-temperature toughness, which comprises heating a steel bloom which contains 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 a temperature of 1050 to 1200°C; completing the hot rolling of the bloom at 870°C or above; cooling, after a lapse of 10 to 90 seconds, the obtained plate at a cooling rate of 5°C/s or above from a temperature of 840°C or above to a temperature of 200°C or below; and then tempering the resulting plate at a temperature of 450 to 650°C for 20 to 60 minutes.
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