| 摘要 |
This hot-rolled steel sheet contains, in terms of mass%, C: 0.015% or more to less than 0.040%; Si: less than 0.05%; Mn: 0.9% or more to 1.8% or less; P: less than 0.02%; S: less than 0.01%; Al: less than 0.1%; N: less than 0.006%; and Ti: 0.05% or more to less than 0.11%, with the remainder being Fe and inevitable impurities, wherein Ti/C is in a range of 2.5 or more to less than 3.5, Nb, Zr, V, Cr, Mo, B and W are not included, a microstructure includes a mixed microstructure of polygonal ferrite and quasi-polygonal ferrite in a proportion of greater than 96%, a maximum tensile strength is 520 MPa or more and less than 720 MPa, an aging index AI is more than 15 MPa, a product of a hole expansion ratio (») % and a total elongation (El) % is 2350 or more, and a fatigue limit is 200 MPa or more.
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