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Application
Salt bath carburizing is used for smaller parts and parts that would otherwise be distorted easily in a
furnace.
However, due to the use of the salt that contains cyanide there are doubts using this treatment from
an environmental standpoint. A heat treatment provider must be aware about proper disposal of
waste.

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Fig. 6. 3 Salt bath carburizing

Pack Carburization

Process description
Pack carburization is a process which involves placing steel items into a furnace in close proximity to
high-carbon items. These high-carbon items include everything from carbon powder, to cast iron
particles, and more. In solid or pack carburising, the components are surrounded by a carburising
medium and placed in a sealed box. The medium is usually coke or charcoal mixed with barium
carbonate. The process is really one of gas carburisation since the CO produced dissociates into CO2
and carbon which diffuses into the components' surface. Temperatures are usually 790 to 845 °C for
times of 2 to 36 hours. Pack carburising is the least sophisticated carburising process and as a result
remains a widely used method (Fig. 6. 4). 5

Benefits
Carburizing offers advantages because it supplies case hardening for the exterior surfaces of low
carbon steel and iron alloys. Metal parts which undergo heat treatment and carburizing tend to resist
abrasions more effectively, for instance.

Application
Packing for pack carburizing is critical for proper process control. In the container, the packing
compound is layered on the bottom to a depth of approximately 25-50mm (1-2 inches). The parts are
then stacked on top of the layer of pack carburizing compound. Sometimes part supports are added
to reduce distortion of the parts. Parts are usually packed 25-50 mm (1-2 inches) apart. Pack
carburizing compound is then applied to the part, completely covering the parts and supports. The
compound is lightly tamped until level, to make sure the parts are completely covered. Finally, the
container is filled with the final layer of compound to a minimum depth of 50 mm HV.

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