Patent ID: 7357843

Claim:
A vacuum heat treating method which is performed while supplying a mixed gas of ethylene gas and hydrogen gas into a depressurized vacuum heat treating furnace, comprising: storing plural settings of equivalent carbon concentration in the processing atmosphere that are determined in advance for obtaining required heat treatment quality, the plural settings of equivalent carbon concentration in correspondence with materials of the workpieces and used as a targeted value; detecting a quantity of ethylene gas and that of hydrogen gas in the vacuum heat treating furnace; 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 quality of an object to be treated inputted in advance, to control quantities of ethylene gas and hydrogen gas supplied into the vacuum heat treating furnace on the basis of a difference between the calculated value and the targeted value.