In vacuum carburizing, propane or acetylene is usually selected for all carburizing processes without any specific geometrical requirements. However, it has been proven that acetylene offers better carbon efficiency compared to propane because of its instability and higher carbon content per mol of gas. Therefore, by using acetylene, densely packed loads, especially parts with complicated shapes can be carburized at high, reproducible

Small quantities of carburizing gas are introduced in the hot zone and are drawn-off by the vacuum pumps. Process parameters like temperature and gas flow are selected according to the parts requirements and are used for the process control. To achieve the specified carbon profile, the carburizing is done in alternating steps for carburizing and diffusion, followed by a final diffusion step. These sequences are also parameters for the process control.

Compared to the processes using atmospheric conditions, vacuum carburizing has a lot of advantages. Due to a higher carbon mass-flow rate, the cycle time is considerably reduced. Vacuum furnaces easily allow higher temperatures, thus process times can be reduced dramatically, especially for bigger case depths.Because of the absence of oxygen (air), the quality and properties of the parts surfaces are improved.

Because of the absence of oxygen (air), the quality and properties of the parts surfaces are improved.