Development of Nitrogen-Hydrocarbon Atmospheric Carburizing and Process Control Methods

Atmospheric pressure carburizing and neutral carbon potential annealing in nitrogen containing small additions of hydrocarbon gases can offer cost and steel surface quality alternatives to the comparable, endothermic atmosphere, or vacuum operations. An experimental program was conducted for refining real-time process control methods in carburizing of AISI 8620 steel under N-2-CH4, N-2-C3H8 blends containing < 5 vol.% of hydrocarbon gas at 900 and 930 A degrees C. Multiple types of gas analyzers were used to monitor residual concentrations of H-2, CO, CO2, H2O, O-2, CH4, C3H8, and other hydrocarbons inside furnace. A modified shim stock technique was additionally evaluated for correlation with gas analysis and diffusional modeling using measured carbon mass flux values (g/cm(2)/s). Results of this evaluation work are presented.