Patent ID: 8465598
Filing Date: 2013-06-18
Classification: C21D,C23C,F27B

Abstract:
1. A vacuum carburization processing method comprising: a preparatory heating step of increasing a 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 less than or equal to 0.1 kPa; 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; 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; a pre-carburization maintaining step, performed between the preparatory heating step and the carburizing step, of maintaining the workpiece at a final temperature of the preparatory heating step, wherein pressure inside the heating chamber is reduced to less than or equal to 1 Pa in the last two minutes of the pre-carburization maintaining step; a normalizing step, performed between the diffusing step and the quenching step, of reducing the temperature of the workpiece so that a 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.