| 摘要 |
PROBLEM TO BE SOLVED: To provide a method capable of manufacturing a cold forging steel material having carbide spheroidized therein.SOLUTION: Carbide in a steel material is spheroidized by cooling the steel material to at least 600°C or less at an average cooling rate of 1°C/second or less in a temperature range from an Apoint to the Apoint minus 40°C after hot-rolling and sequentially processing the following first heating-holding, second heating-holding, first cooling and second cooling: (1) the first heating-holding for a residence time of 150 minutes or more in the temperature range of the Apoint minus 30°C, or more and less than the Apoint plus 5°C; (2) the second heating-holding at a heating rate (an average heating rate of the Aplus 5°C to the Apoint plus 15°C) of 12°C/hour or more for a residence time of 10-300 minutes in a temperature range of the Aplus 15°C to the Apoint plus 60°C; (3) the first cooling at a cooling rate (an average cooling rate of the Apoint plus 15°C to the Apoint plus 5°C) of 10°C/hour or more; and (4) the second cooling at a cooling rate (an average cooling rate of the Apoint to the Apoint minus 30°C) of less than 10°C/hour. |
