| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold-rolled high-tensile-strength steel sheet which is superior in drawability and secondary-working embrittlement resistance, and to provide a high-tensile-strength galvanized steel sheet and a manufacturing method therefor. SOLUTION: This cold-rolled high-tensile-strength steel sheet has a component composition including 0.004% to 0.008% C, at most 0.1% Si, 0.5% to 2.5% Mn, 0.02% to 0.10% P, at most 0.02% S, 0.01% to 0.08% Al, at most 0.005% N, Nb in an amount of satisfying the expression of 1.0≤([Nb]/93)/([C]/12+[N]/14)≤3.0, wherein [Nb], [C] and [N] represent contents (mass%) of Nb, C and N, respectively, and the balance Fe with unavoidable impurities. Also, the sheet has a single phase structure of ferrite with a mean crystal grain size of 20μm or smaller, in which the acicular ferrite occupies more than 95% by volume fraction. One part of the above Nb can be replaced by Ti. COPYRIGHT: (C)2008,JPO&INPIT
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