Patent attributes
The present invention provides a vacuum heat treating method, such as carburization, carbonitridation, high temperature carburization, high concentration carburization and the like, performed while supplying a mixed gas of ethylene gas and hydrogen gas under reduced pressures. The method includes: detecting a quantity of ethylene gas and that of hydrogen gas in a vacuum heat treating furnace (1); calculating an equivalent carbon concentration of atmosphere on the basis of the detected quantity of ethylene gas and that of hydrogen gas; and comparing the calculated value with a targeted value which is set on the basis of a material specification and required heat treatment performance of an object to be treated (a workpiece), to control quantities of ethylene gas and hydrogen gas supplied into the vacuum heat treating furnace (1) on the basis of a difference between the calculated value and the targeted value. A heat treatment quality required for the workpiece can be obtained with accuracy and reproducibility.
