Process Of Duplex Treatment Of Plasma Nitrocarburizing And Post-oxidation For Structural Steel And It’s Properties

Structural steels are the important metallic materials applied in modern industrialbecause of their good mechanical properties and relatively low cost. However, they generallyhave poor wear resistance and corrosion resistance, which are not favorable for someapplications. Since the wearing and corrosion start from the surface, surface modificationtechnology is the focus of research in order to improve the corrosion resistance and wearresistance of structural steels. Previous work showed that the duplex treatment of plasmanitrocarburizing and post-oxidation can remarkably improve both the wear resistance andcorrosion resistance. Furthermore, the duplex treatment has many other advantages, such asthe environment friendliness, short treatment period and low energy consumption.This dissertation firstly presents the study focused on optimizing process parameters ofplasma nitrocarburizing treatment. The optimized process parameter of plasmanitrocarburizing for gaining the thickest compound layer and best wears resistance wereobtained. The effects of N2/H2ratio, CO2percentage, temperature and pressure on thethickness and hardness of compound layer after plasma nitrocarburizing were investigated.The wear resistance of the nitrocarburized surface prepared by different process parameterswas tested. Results showed that the thickest compound layer was28.52μm, and the highesthardness was745HV0.3. Good wear resistance was obtained with the friction coefficient of0.3340and the width of friction trances of381.69μm. The employed optimum plasmanitrocarburizing conditions include N2:H2=1:1, CO2percentage of3%, temperatureT=500℃, and pressure P=500Pa.The optimization of process parameters of plasma post-oxidation treatment was alsopresented after plasma nitrocarburizing. The work aims at finding out the process parametersof plasma nitrocarburizing+post-oxidation treatment to achieve the best corrosion resistanceand, meanwhile, to improve the wear resistance. The effects of H2/O2ratio, temperature andpressure on the corrosion resistance and wear resistance were studied. The processingparameters that enhance the corrosion resistance and wear resistance were obtained. Theoptimized post-oxidation treatment parameters involve the H2:O2=8:1, temperature T=500℃,and pressure P=400Pa. Under this optimized process, the excellent corrosion resistance wasobtained. The potentiodynamic polarization was higher. The time before the appearance ofrust was700h. The friction coefficient was0.2689, and the width of friction trances was385.15μm.