A method of controlling an oxygen-free heat treating process in an atmospheric pressure furnace is disclosed. The present method employs an oxygen-free gas atmosphere including hydrogen gas in concentrations between about 1.0 percent to 10.0 percent, a hydrocarbon gas, such as propylene, in concentrations of between about 0.1 percent and 10.0 percent that varies as a function of time, with the balance of the gas atmosphere being nitrogen. The presently disclosed oxygen-free carburization process uses a precisely controlled gas atmosphere to minimize inter-granular oxidation, eliminate the formation of soot and cementite, and avoid hydrogen embrittlement.