| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having excellent stretch flange formability, also having excellent uniformity of the material in a coil, and having a tensile strength of≥540 MPa. SOLUTION: Regarding the method for producing a high stretch flange formability hot rolled steel sheet having a tensile strength of≥540 MPa, and having excellent uniformity in the material, at the time when a steel having a composition comprising, by mass, 0.01 to <0.08% C, 0.06 to 2.0% Si, 0.96 to 3.0% Mn,≤0.10% P,≤0.01% S,≤0.3% Al,≤0.01% N and 0.01 to 0.20% Ti, also satisfying Mn-Si>0.9%, and also satisfying the inequality (1), and the balance Fe with inevitable impurities is hot-rolled, finishing temperature is controlled to≥900°C, and coiling is performed at 400 to 600°C: the inequality (1) is 0.75≤[(C%/12)/ä(Ti%/48)+(Nb%/93)+(Mo%/96)+(V%/51)-(N%/14)-(S%/32)}]≤1.25. COPYRIGHT: (C)2006,JPO&NCIPI
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