| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength, cold-rolled, thin steel sheet and a high strength, zinc plated thin steel sheet, each of which not only has good surface quality, non age-hardening property and workability applicable to automotive exterior panels but also superior brittleness resistance against secondary fabrication, and a production method for the same. SOLUTION: The high strength thin steel sheet has the chemical composition consisting of, by mass, 0.0040-0.02% carbon, 1.0% or less silicon, 0.7-3.0% manganese, 0.02-0.15% phosphorus, 0.02% or less tin, 0.01-0.1% aluminum, 0.004% or less nickel, 0.2% or less niobium, and the balance substantially iron, and satisfies the two formulas (12/93)×Nbx/C>=1.0 and Nb*Nb-(93/14)×N, wherein C, N and Nb are in terms of mass %. It also satisfies the formula YP<=-120×d+1280 with respect to metal structure and temper, wherein YP is yield strength [MPa] and (d) is average ferrite grain diameter [μm]. In the figure, the area represented by a bold arrow on the right hand side of a perforated line indicates the scope of this invention.
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