VACUUM CARBURIZATION METHOD AND VACUUM CARBURIZING APPARATUS

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PROBLEM TO BE SOLVED : To provide a vacuum carburization method and a vacuum carburizing apparatus which achieve the uniform temperature between a surface and the inside of a workpiece in the high-temperature treatment even when the progression of carburization and diffusion is accelerated to shorten the treatment time by increasing the treatment time, and which provide the workpiece having the predetermined physical properties by suppressing the coarsening of crystal grains. SOLUTION : The vacuum carburization method includes : a normalizing step of performing the step cooling of alternately repeating the temperature-dropping treatment and the temperature-keeping treatment for a plurality of times so that the temperature history of the temperature of a workpiece from the first temperature to the predetermined temperature satisfies the predetermined condition between the diffusion step and the hardening step; a post-normalizing maintaining step of refining crystal grains of the workpiece by maintaining the temperature for a predetermined time so that the temperature of the entire workpiece reaches a predetermined value after the normalizing step; and a re-heating step of raising the temperature of the workpiece to the second temperature after the post-normalizing maintaining step. COPYRIGHT : (C)2008, JPO&INPIT