| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-carbon hot rolled steel sheet with high hardenability, which can be produced without employing high temperature and multistage annealing, hardly generates cracks due to press forming and cold forging, is extremely soft, and has superior workability. SOLUTION: The method for manufacturing a high-carbon hot rolled steel sheet with hardenability comprises hot rolling a steel containing C of 0.2-0.7 mass % to control the structure so as to have a bainite phase with a volume factor of greater than 20%, and annealing it to make a spheroidizing structure. The method further comprises hot rolling the steel at a finishing temperature (Ar3 transformation point -20 deg.C) or higher, cooling it at a higher cooling rate than 120 deg.C/second and at a cooling finishing temperature of 620 deg.C or lower, subsequently winding it up at a winding temperature of 600 deg.C or lower, pickling it, then annealing it at an annealing temperature of 640 deg.C or higher but Ac1 transformation point or lower. Alternatively, the method can include controlling the structure so as to have the bainite phase with a volume factor of greater than 70%, or further cooling it at the finishing temperature of 550 deg.C or lower, and winding it at a winding temperature of 500 deg.C or lower.
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