| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel sheet excellent in surface characteristic and stretch- flange formability, and its manufacture. SOLUTION: The steel sheet, contains, by weight, >=0.010% C, <=1.0% Si, <=3.0% Mn, <=0.15% P, <=0.05% S, <=0.01% N, 0.010-0.50% Ti, 0.001-0.1% Nb, 0.0001-0.05% B, and <=0.0005% Ca and/or metallic REM and also contains 0.005-0.1 wt.% of non-oxide Ti(Ti*) and contains Al in an amount satisfying (1) wt.% Ti/wt.% Al>=5 or (2) Al<=0.010 wt.% and wt.% Ti/wt.% Al<5, and further, the average size of oxide inclusions is regulated to <=3μm and >=90% of the oxide inclusions contains the oxide inclusions with a size of <=10μm. At the time of its manufacture, a slab is heated and soaked at 900 to 1,300 deg.C, finish rolling is finished at 650 to 960 deg.C, coiling is done at 400 to 750 deg.C, cold rolling is carried out at 50 to 95% draft, and the resultant sheet is subjected to recrystallization annealing at 700 to 920 deg.C.
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