| 摘要 |
PURPOSE:To manufacture a cold-rolled steel sheet excellent in workability in high efficiency, by subjecting a continuously cast steel slab with a specific composition consisting of C, Mn, Al, N, Ti, and Fe to specific hot rolling, cold rolling, and continuous annealing. CONSTITUTION:A continuously cast slab of a steel having a composition which consists of, by weight, <=0.0030% C, 0.03-0.80% Mn, 0.04-0.12% sol.Al, 0.0050-0.0120% N, 0.002-0.025% Ti, and the balance Fe with inevitable impurities and in which Ti<=(N-0.0030)48/14 is satisfied is hot-rolled at 700-970 deg.C finishing temp. Then, the hot-rolled steel plate is wound up at a temp. as low as <=560 deg.C to prevent the precipitation of fixed AlN. The resulting hot-rolled plate is descaled and then cold-rolled at 65-85% draft to improve r45. Subsequently, the cold-rolled steel sheet is continuously annealed under the conditions of 15-300sec temp.-rise time up to 400-700 deg.C and 700-900 deg.C maximum heating temp. to accelerate AlN precipitation and recrystallization. In this way, the cold-rolled steel sheet excellent in workability and having high r45 can be obtained.
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