| 摘要 |
There are provided a method, between a diffusion process and a quenching process, a normalizing process of performing step cooling in which a temperature lowering treatment and a temperature keeping treatment are alternately repeated plural times so that a temperature history from the first temperature to a predetermined temperature satisfies a predetermined condition; an after-normalizing maintaining process of maintaining the temperature of the whole workpiece for a predetermined time after the normalizing process so that the whole workpiece becomes the predetermined temperature, thereby producing fine crystal grains in the workpiece; and a reheating process of raising the temperature of the workpiece to the second temperature, after the after-normalizing keeping process. According to the invention, even when a process temperature is set high to make rapid progress of carburization and diffusion and thus the process time is shortened, uniformity in temperature is achieved between a surface and a inside of a workpiece by the high-temperature process and crystal grains are prevented from being coarse, thereby obtaining a workpiece having a predetermined property value.
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