| 摘要 |
PURPOSE:To easily manufacture a high-tensile hot-rolled sheet metal excellent in delayed ageing characteristic at ordinary temp. and baking hardenability and having superior workability, by subjecting a steel having a specific composition containing C, Mn, P, Al, and N to specific hot rolling, cooling, and winding. CONSTITUTION:A steel containing, by weight, 0.02-0.10% C, 0.5-1.2% Mn, 0.04-0.10% P, 0.02-0.05% Al, and 0.005-0.020% N is hot-rolled at a temp. of Ar3-20 deg.C or above. Subsequently, the hot rolled steel plate is cooled at >=30 deg.C/s average cooling rate so as to inhibit AlN precipitation and also to provide a fine ferritic structure. Then, winding is carried out at 150-450 deg.C so as to accelerate the proper precipitation of C. By this method, the high-tensile hot-rolled sheet metal showing baking hardening amount as high as >=about 5kgf/mm<2>, practically free from age deterioration at room temp., and having superior workability of about 40-50kgf/mm<2> by T.S. can be obtained.
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