| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet having strength of a≥590N/mm<SP>2</SP>class and excellent in elongation, hole expansibility and secondary working crack properties intended for an automobile component to be subjected to press working, and to provide a production method therefor. SOLUTION: The high strength hot rolled steel sheet excellent in elongation, hole expansibility and secondary working crack properties has a steel structure in which the fraction of martensite is≥5%, and the balance ferrite and bainite, and the fraction of retained austenite is≤2% and the fraction of martensite is <1%. In the method of producing a high strength hot rolled steel sheet excellent in elongation, hole expansibility and secondary working properties, rolling is performed in such a manner that the finishing temperature is controlled to an Ar<SB>3</SB>transformation point or higher, and, after coiling at≤200°C, reheating is performed again under the conditions shown in the inequality (1): 12,000≤(T+273)×(log(t/60)+19.8)≤17,000 (1); wherein T is heat treatment temperature (°C), and t is treatment time (min). COPYRIGHT: (C)2005,JPO&NCIPI
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