| 摘要 |
PROBLEM TO BE SOLVED: To obtain a B-added soft cold-rolled steel sheet excellent in structural stability in high temp. annealing by allowing the steel sheet to have a compsn. contg. specified amounts of C, Si, Mn, P, S, N and B, in which B, N and Al satisfy a specified relation, and the balance Fe with inevitable impurities. SOLUTION: This steel sheet has a compsn. contg., by weight, 0.01 to 0.03% C, <=0.1% Si, <=0.5% Mn, <=0.03% P, <=0.03% S, <=0.0035% N and <=0.0035% B, also satisfying B/N=0.6 to 1.5 by a stoichiometric ratio and Al<=0.035×√(B/N×0.6), and the balance Fe with inevitable impurities. As for the above B/N ratio, in the case of <0.6, the amt. of fine AlN to be precipitated is increased, in the case of >1.5, B is formed in the steel, and in both cases, the steel is hardened, therefore, it is extremely important. Moreover, since Al is used as an oxidizing agent, it is contained by a certain degree, but, by prescribing the Al content to the above, the precipitation of AlN is delayed, its precipitation into the unrecrystallized part is evaded, and the generation of mixed grains is suppressed.
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