| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a thick, high-tension, hot-rolled steel sheet, which has high strength of≥510 MPa TS and high ductility in combination and is well balanced between the strength and the durability and further, exhibits excellent low-temperature toughness. SOLUTION: The steel material having a composition containing 0.02-0.08% C, 0.01-0.10% Nb, 0.001-0.05% Ti, so as to satisfy äTi+(Nb/2)}/C<4, is heated and subjected to the hot-rolling, and then subjected to a primary and a secondary accelerative coolings at≥10°C/s cooling speed in the center part of the sheet thickness, and then, winding is performed at a prescribed winding temperature. In the primary accelerative cooling, the cooling is performed up to a primary cooling-stop temperature of≥500°C so that the cooling speed difference between the surface layer and the center part of the sheet thickness becomes <80°C/s. In the secondary accelerative cooling, the cooling wherein the cooling speed difference between the surface layer and the center part of the sheet thickness becomes≥80°C/s, is performed up to a specific cooling-stop temperature or lower depending on the alloy element contents and the cooling speed. Further, the winding temperature is set to a specific temperature or lower, depending on the alloy element contents. COPYRIGHT: (C)2010,JPO&INPIT |
