Study On Ion Oxynitriding And Ion Nitriding Post Aging & Oxidizing Processes

In industry, most of failures of machine parts often begin from their surfaces, so it is important to explore new surface-strengthening technologies in order to improve their durability. Glow discharge nitriding, which is a thermochemical process to improve the wear, fatigue and corrosion resistance of a variety of engineering steels, is widely used for modern industries. The treatment involves the introduction of active nitrogen atoms into the component surface to produce a modified layer, consisting of an outer compound layer and an inner diffusion layer. Recently, research and development of combined processes on the basis of ion nitriding are focus in this area. In this paper, C45 and 40Cr steel samples were treated by ion oxynitriding and ion nitriding-aging + oxidizing processes. The constitution of phases, the microstructure and the properties of the modified layers were studied with Microscopy, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Microhardness Apparatus and MM-200 Wearing Machine. The results were contracted with samples treated by ordinary ion nitriding.The results revealed that ion oxynitriding when 10～20% air was added in the atmosphere of ammonia would increase the nitrogen concentration of the samples surface, accelerate the nitriding process , and that the effective case depths and the hardness gradient of modified layer of experimental samples would be improved at the same time. Furthermore, the tribological and electrochemical behavior of the samples were improved as magnetite Fe3O4 was obtained during the treatment. By the new kind of process, the components performed will have well corrosion and wear resistance. When 40Cr steel samples were treated with aging and oxidizing process after ion nitriding, the phase transformation and the alloy nitride CrN precipitation would occur in the compound layer, which lead to a considerable enhancement of the hardness of modified layer. A thin magnetite superficial layer outer of the compound layer was obtained, which will further improve the corrosion resistance of the nitrided steel. As a result, both of the wear and corrosion resistance were improved by post aging and oxidizing process. Aging and oxidizing in low temperature and low air pressure will maximize the properties characteristics of the nitrided steel. In the two processes, air was added directly as oxidation atmosphere. The results show that the combination treatments were very effective against both wear and corrosion. These new kinds of processes will have great applications with simple technological operation, unchanging expedience and well mechanical properties.