| 摘要 |
PURPOSE:To manufacture a hot-rolled steel plate stably excellent in workability even if rolling and cooling temps. fluctuate, by adding specific amounts of B, Nb, and Ti to steel and by carrying out hot rolling by regulating finishing temp. CONSTITUTION:A steel having a composition which consists of, by weight, <=0.08% C, 0.1-0.4% Mn, <0.01% Si, 0.02-0.08% acid-soluble Al, 0.005-0.020%, in total, of Nb and/or Ti, 0.0015-0.0060% B, <=0.010% N, and the balance Fe with inevitable impurities and in which B/8>N/14 is satisfied is refined. This steel is cast into a slab, which is hot-rolled at >=850 deg.C finishing temp. Since the steel of this composition has low Ar3 transformation point, finishing temp. can be lowered and rolling temp. region can be enlarged. As a result, the hot-rolled steel plate excellent in workability even if rolling conditions fluctuate can be stably manufactured in high efficiency without elevating slab- heating temp.
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