| 摘要 |
PROBLEM TO BE SOLVED: To provide a vacuum carburization processing method and a vacuum carburization processing apparatus capable of ensuring the quality by suppressing the coarsening of crystal grains caused by the high-temperature processing even when the processing time is shortened by expediting advancement of carburization and diffusion by raising the processing temperature. SOLUTION: A vacuum carburization processing method includes a preheating step of increasing the temperature of a workpiece in a heating chamber to a first temperature, a carburizing step of carburizing the workpiece by supplying carburizing gas into the heating chamber from a state where the pressure inside the heating chamber is reduced to an extremely low pressure, a diffusing step of terminating the supply of the carburizing gas and making carbon diffuse from a surface of the workpiece into its internal part, and a quenching step of abruptly cooling the temperature of the workpiece from a state where the temperature of the workpiece is at a second temperature; and also includes, between the diffusing step and the quenching step, a normalizing step of reducing the temperature of the workpiece so that the temperature history of the workpiece from the first temperature to a predetermined temperature satisfies predetermined conditions, a post-normalization maintaining step, performed after the normalizing step, of miniaturizing crystal grains of the workpiece by maintaining the workpiece at the predetermined temperature for a predetermined time so that the entire workpiece reaches the predetermined temperature, and a reheating step, performed after the post-normalization maintaining step, of increasing the temperature of the workpiece to the second temperature. COPYRIGHT: (C)2008,JPO&INPIT
|
