| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength thin steel sheet which has a high ductility and an excellent stretch-flange property in a range of about 700-1300 MPa in tensile strength and its manufacturing method. SOLUTION: The steel sheet (x), which is manufactured properly employing a rolling mill 1 and a continuous annealing facility 2, contains 0.10-0.22% C,≤0.30% Si, 1.0-2.2% Mn, 0.10-0.22% Ti by mass %, and has a composite structure including martensite with the average grain diameter of 5μm or less dispersed in ferrite with the average grain diameter of 5μm or less, in which a volume % of martensite is 5-30%. The steel sheet is not only excellent in tensile strength, ductility and stretch-flange property but also desirable in plating performance. COPYRIGHT: (C)2005,JPO&NCIPI
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