Activated atmosphere case hardening of steels

Wang, Xiaolan

Etd

Activated atmosphere case hardening of steels

Público

Case hardening, a process which includes a wide variety of techniques, is used to improve the wear resistance, by diffusing carbon (carburization), nitrogen (nitriding) and/or boron (boriding) into the outer layer of the steel at high temperature, and then heat treating the surface layer to the desired hardness without affecting the softer, tough interior of the part. In this research, a nitrogen-hydrocarbon gas mixture was used as the process atmosphere for carburizing steels. It can offer a cost and part quality alternative to the conventional endothermic atmosphere and vacuum processes. It can hold the promise for matching the quality of work parts processed in vacuum furnace, i.e. eliminating the intergranular oxidation which normally occurs in the endogas atmosphere. The process control of nitrogen-hydrocarbon atmosphere is also investigated in the research. Modified shim stock method is used to measure the carbon pickup and constant carbon flux modeling tool is used afterwards to predict the carbon profile. With minimum modification, commercially available equipment or sensors can be used to monitor non-equilibrium process atmosphere. Gas nitriding was also studied. For nitriding, the kinetics of the nitriding process with hydrocarbon gases addition and electric arc discharge activation of the nitrogen diluted ammonia atmosphere were investigated. Prior to and during the nitriding, hydrocarbon gases were reacted with metal surface and removed oxidation layers, which can accelerate nitriding process. Overall, nitriding with this unique gas mixture provides an alternative to a long-hour pure ammonia nitriding with more efficient energy utilization. The main objective of this project is to develop the conventional, atmospheric-pressure, low-cost surface hardening treatments for the case hardening of carbon, alloy and stainless steel. The possibility of plasma activation of atmosphere and metal surface to shorten processing time and save energy and time is investigated in this research. The process atmosphere is safer, more efficient, less toxic and less flammable.

Creator