| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot-rolled ultrasoft high-carbon steel plate excellent in workability. SOLUTION: The hot-rolled high-carbon steel plate contains 0.2 to 0.7% C and has a structure having an average grain size of ferrite of 20 μm or above, a volume ratio of ferrite grains having diameters of 10 μm or below of 20% or below, an average grain size of carbides of 0.10 μm or above and below 2.0 μm, a ratio of carbides having aspect ratios of 5 or above of 15% or below, and a carbide-carbide contact ratio of 20% or below. Also, a process for the production thereof comprises: rough rolling and subsequently finish rolling at an inlet temperature of finish rolling of 1100°C or below, a final pass reduction of 12% or above, and a finish temperature of (Ar3-10)°C or above; primary cooling conducted within 1.8 seconds after the finish rolling at a cooling rate exceeding 120°C/s to a cooling stop temperature of 600°C or below; keeping at a temperature of 600°C or below by secondary cooling; taking-up at a temperature of 580°C or below; and pickling and then spheroidizing by box annealing at a temperature of 680°C or above and up to Ac1 transformation point. COPYRIGHT: (C)2008,JPO&INPIT
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