Z. Zurecki, Air Products & Chemicals, Inc., Allentown, PA; X. Wang, Worcester Polytechnic Institute, Worcester, MA
Nitrogen-hydrocarbon gas atmospheres can offer a cost and part quality alternative to the conventional endothermic atmosphere and vacuum processes. Non-flammable, low percentage methane and nitrogen mixtures were activated during furnace injection by a novel, non-thermal electric discharge (cold plasma) method and used in carburizing process. Theoretical and experimental investigation has been carried out including box furnace tests at atmospheric pressure to examine the efficiency of activated mixtures in carburizing AISI 1010 shim stock and AISI 8620 steel parts between 875oC and 975oC. Laser gas analyzer was used to monitor changes in furnace CH4, H2, CO, CO2, H2O and residual O2 concentrations during the process. Carbon mass flux (J, g/cm2/sec), potential (Cp), activity (ac) and carbon concentrations were evaluated. SEM-EDS examination has shown that, in addition to improving microhardness profile and increasing effective case depth, the new method eliminated internal oxidation defects identified in the comparable endo-carburized steel parts.
Summary: Nitrogen-hydrocarbon gas atmospheres can offer a cost and part quality alternative to the conventional endothermic atmospheres. Rate of carburization by various nitrogen-based hydrocarbon mixtures has been investigated both theoretically and experimentally. Non-flammable, low percentage methane and nitrogen mixtures were activated during furnace injection by a novel, non-thermal electric arc discharge method and used in carburizing process. A series of experiments have been carried out in box furnace and micro-balance apparatus (TGA/DSC) to examine the efficiency of activated mixtures in carburizing of steel at 875oC and 975oC. Laser gas analyzer was used to monitor, real-time, changes in furnace N2, CH4, H2, CO, H2O, and residual O2 concentrations during the process. Carbon mass flux (g/cm2/sec), carbon potential (Cp), and carbon profiles were measured using shim stock and test coupons. Results of this study will be presented along with test data concerning industrial products.
