| 摘要 |
PROBLEM TO BE SOLVED: To stably and economically produce a high tension steel plate having >=590 N/mm2 yield strength and >=690 N/mm2 tensile strength. SOLUTION: The steel having the composition composed of 0.04-0.15 wt.% C, 0.1-1.0 wt.% Si, 1.4-2.0 wt.% Mn, 0.02-0.08 wt.% Nb, 0.04-0.20 wt.% Ti and the balance Fe with inevitable impurities, is heated to 1,100-1,300 deg.C, and the rolling is completed at a temperature not lower than Ar3 transformation point and successively, this rolled steel is cooled to 650-350 deg.C at >=10 deg.C/sec speed, and after cooling, this steel is reheated and held to 400-700 deg.C for >=60 sec and tempering is executed to precipitate TiC in fine bainite structure.
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