Research On Ion-nitrocarburizing Processes And Mechanism With N₂ And CH₄ For 40Cr

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. Ion nitriding is well–known surface modification technique extensively used in the modern industries to enhance the mechanical properties of nitrogen layer, shorten the period of production, reduce the formation of workpiece etc. Recently, research and development of combined processes on the basis of ion nitriding, economized energy sources and decreased environmental contamination are focus in this area. The paper discusses 40Cr Steel which was treated by compound treatment method of N, C co-diffusing with N2 and CH4. its idea is what decreases environmental contamination and substitutes NH3 for N2.The constitution of phases, the microstructure and the properties of the modified layers were analyzed using Microscopy, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Microhardness Apparatus and MRH-3 Wearing Machine, and were compared with those treated by conventional nitriding. The mechanism of the ion N-C component permeation is discussed in the end of this article. The results in this paper are following:①the composite layer of 40Cr Steel which is treated by compound treatment method of N, C co-diffusing, can divide into three layers. The surface layer is chiefly N,C compound. The second layer is diffused layer. The third layer is basic structure. When voltage of test was 600V, depth of the compound layer was deepest.②when proportion of N2 to CH4 is constant, microhardness of sample surface enhance as voltage of test reduce; when voltage of test is constant, as CH4 increases, the max hardness heightens and composite layer obtained is deeper.③Phase composition of the composite layer main containεphase(N,C compound); when ion nitrocarburizing process is changed, composite layer may be include Fe2N, Fe4N and Fe3C phase.its wear resistance and corrosion resistant property is the best with singleεphase.④t he CH4 plays important roles in ion-nitrocarburizing. It decomposes carbon which provide physical premise of carburizing and accelerate nucleation of nitride. It decomposes H·which serve as shot to clean out surface passivation and improve surface activation, H·has more important which transfer energy itself to N2 when impact each other. So voltage threshold of producing active nitrogen atoms is reduced more.⑤I on-nitrocarburizing Technique with N2 and CH4 is available and friendly to environment.