| 摘要 |
PURPOSE:To obtain an unnormalized high-tension steel plate having excellent toughness by subjecting an ingot contg. respectively specific ratios of Cr, Si, Mn, and Nb to heating and rolling as well as cooling under controlled conditions in order to sufficiently exhibit the effect of Nb in particular. CONSTITUTION:The ingot contg., by weight %, <=0.2% C, 0.1-0.5% Si, 0.6-2.0% Mn, 0.005-0.05% Nb is treated as follows: Said ingot is heated for >=1hr at the temp. from the Ac3 transformation point at which carbonitride of Nb exists in an unsolutionized state up to 950 deg.C to obtain fine and uniform austenite grains. The ingot after the heating is then heated for >=10min at 1,130-1,150 deg.C to solutionize >=80% of the Nb of the equil. solutionization rate at this heating temp. The ingot after said heating is rolled at >=70% total draft in the uncrystal region and is finished at 700-800 deg.C. The rolled steel is immediately cooled down to 400-550 deg.C at 5-15 deg.C/sec cooling rate, by which the desired high-tension high-toughness steel plate is obtd.
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