Carburizing atmosphere was endothermically generated by conversion of the mixed gas consisting of propane gas, as a by-product of petroleum industry, and air. This atmosphere contained substantially none of the oxidizing gases, but appreciable amounts of reducing gases, carbon monoxide and hydrogen. The endothermic generator consisted of a mixing pump and an externally heated retort in which the gas-air reaction took place in the presence of a nickel catalyst. The endothermic atmosphere was successfully used for carburization of steel. It was also demonstrated in this experiment that the above endothermic atmosphere, with proper adjustment of the dew point or the water vapor content of the gas, could be used to control the surface carbon content of steel during carburizing treatment.
