| 摘要 |
Provided is a hot-rolled thin steel sheet having a thickness of less than 6 mm and having high strength showing a tensile strength of 440 MPa or more, excellent formability, and excellent strength and toughness after heat treatment and a method of manufacturing the same. A steel base material containing 0.10 to 0.20% of C, and Si, Mn, Al, P, S, and N adjusted to suitable amount ranges, and 0.01 to 0.15% of Ti and 0.0005 to 0.0050% of B is hot rolled so as to have a finishing temperature of finish rolling of 820 to 880°C; after the completion of the rolling, the hot-rolled thin steel sheet is cooled to a surface temperature range of 550 to 650°C at a surface cooling rate of 15 to 50°C/s; and the hot-rolled thin steel sheet is coiled at the temperature range. By doing so, the structure can be uniform in the thickness direction and be a bainitic ferrite phase. The hot-rolled steel sheet has high strength showing a tensile strength of 440 to 640 MPa and high ductility showing an elongation of 20% or more and further can be produced into a product having high strength showing a tensile strength of 980 MPa or more and high toughness showing a vTrs of -100°C or less by forming/heat treatment.
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