Pack carburizing is a process of packing parts in a high carbon medium such as
carbon powder or cast iron shavings and heated in a furnace for 12 to 72 hours at 900 ºC
(1652 ºF). CO gas is produced at this temperature which is a strong reducing agent. Due
to high temperature, carbon is diffused into the surface as the reduction reaction occurs
on the surface of the steel. Based on experimental and theoretical calculations on
diffusion theory the parts are removed and can be subject to the normal hardening
methods when enough carbon is absorbed inside the part (Krauss G, 1991)
During the process the part which needed to be carburized is packed in a steel
container and surrounded by granules of charcoal. The charcoal is treated with an
activating chemical such as Barium Carbonate (BaBO3) that promotes the formation of
Carbon Dioxide (CO2). CO2 will then react with the excess carbon in the charcoal to
produce carbon monoxide (CO). Next, carbon monoxide will react with low carbon
steel surface to form atomic carbon which diffuses into the steel. Carbon gradient
supplied by Carbon Monoxide is necessary for diffusion. It is to be noted that,
carburizing process does not harden the steel but it just only increases the carbon
content to some predetermined depth below the surface to a sufficient level to allow
subsequent quench hardening