This paper explains the technology of heat treatment of three types of gears made of low-alloy steel Č4320 (EN 16MnCr5) and Č4721 (EN 20CrMo5) whose production is large series. Based on the requirements, the analysis and adoption of the process of cementation, hardening and tempering and problems that may occur during operation, are given. The heat treatment plant for these gears has been defined, as well as the list of required furnaces and devices. Finally, a thermal calculation of the cementation furnace and the conceptual design of the heat treatment plant plan are given