Study On Plasma Nitriding And Nitrocarburizing Of Stainless Steel Active Scree

Active screen plasma nitriding(ASPN)is a new nitriding technique in recent years,which can get the same layers as traditional nitriding technique(DCPN).Besides,it can deal with many problems occurring in the conventional nitriding technique,such as surface damage by arcing,heterogeneous chamber temperature,the edging problems and so on,with the theoretical and practical application significance.The effect of ASPNC temperature,chamber pressure and air composition on the microstructure and corrosion property in 3Cr13 martensitic stainless steel and 304 austenitic stainless steels was studied.The layer morphology and micro structure were analyzed by optical microscopy(OM),scanning electron microscope(SEM)and X-ray diffraction(XRD).The microhardness,tribological behaviors and corrosion property were tested by micro-hardness testing,ball-on-disc wear tester and three electrodes system.Through the orthogonal experiment,the significance of each dimension on the thickness and microhardness of the nitriding layer was sorted as ASPN temperature,chamber air pressure and cathode voltage.ASPN temperature has the largest effect on the thickness and microhardness of the layer for stainless steels,while chamber air pressure affects the layer microhardness clearly.And the rate of nitrocarburizing process is faster than the nitriding process.For 3Cr13 martensitic stainless steel,the optimal nitrocarburizing treatment process parameters for improving the abrasive resistance and corrosion resistance are as follws:450℃,300Pa,1:3(N2/H2 ratio).Under this process,the layer is composed of α’N phase,small amount of ε and γ’ phases.The thickness,micro-hardness and friction coefficient of the layer are about 59μm,852HV0.01,0.512 respectively.Comparing with the untreated stainless steel,the wear rate of the specimen reduces from 8.06×10-5 mm3·N-1·m-1 to 7.5×10-6 mm3·N-1·m-1.And corrosion resistance is improved significantly.For 304 austenitic stainless steel,the optimal nitrocarburizing treatment process parameters for improving the abrasive resistance and corrosion resistance are as follws:480℃,400Pa,1:3(N2/H2 ratio).The white bright layer is composed of γN phase,small amount of ε-Fe3C phase,εFe3N and Cr7C3 phase.The thickness,micro-hardness and friction coefficient of the layer are about 6μm,1082HK0.01,0.560 respectively.Comparing with the untreated,the wear rate of the specimen reduces from 1.08×10-4 mm3·N-1·m-1 to 1.67×10-6 mm3·N·m-1,that is,wear resistance of the sample is improved about 64 times,and corrosion resistance is also improved significantly.