Low-pressure Processes

Vacuum carburizing using methane (CH₄) as the carburizing gas was developed in the United States in the 1960s and is now used worldwide. Carburizing technology based on methane requires higher temperatures and pressures up to 500 mbar (375 torr).

This process does not always provide the uniformity and repeatability needed to meet today's specifications for precision parts. Other drawbacks include the cost of oil disposal and a high furnace maintenance requirement. To avoid these problems, new technologies have been developed that use propane (C₃H₈), ethylene (C₂H₄), or acetylene (CH₂) for carburizing at pressures below 20 mbar (15 torr).

At these low pressures and with a carburizing gas properly distributed, carbon penetration is increased throughout the load. Thermal dissociation of the hydrocarbons takes only a couple of seconds, providing sufficient time to react with the hot load surface but not long enough to create soot or tar on furnace parts. This low-pressure vacuum carburizing process is being applied to a wide range of components in a variety of industries.