Abstract: Ferrous articles are heat treated by introducing a gaseous carbon source and an inert carrier gas into a heat treating furnace containing the ferrous articles. The heat treating process is controlled by determining the amount of carbon monoxide resulting from reactions in the furnace and controlling the amount of inert carrier gas in the furnace in response to the amount of carbon monoxide in the furnace atmosphere to control the carbon potential to a desired level by minimizing the effect of equilibrium reactions. Best results are achieved when the amount of carbon monoxide is less than about 3%, preferably, less than about 1%, by volume. Controlling the carbon monoxide level will minimize the effect of harmful decarburizing agents (oxygen, carbon dioxide and water vapor). Under the reaction conditions existing within the furnace operated in accordance with the present invention, hydrocarbon dissociation reaction and primary carburizing reaction are nonequilibrium reactions and control the process results.