Study On The Technology Of Plasma Arc Assisted Nitriding Austenitic Stainless Steel In Low Temperature And Low Pressure

316L austenitic stainless steel is usually used in heat exchangers,food industry,chemical industry and watch industry because of its good corrosion resistance,high-temperature strength and non-magnetic,etc.However,its hardness and wear resistance are relatively poor.When used in mechanical parts which require higher hardness and stronger wear-resistant parts,316L austenitic stainless steel is difficult to meet the requirements,and the service life of these parts are greatly reduced.In this research,hollow cathode DC arc assisted to conduct low-temperature and low-pressure plasma nitriding.The effects of different technological parameters on the microstructure and the properties of 316L austenitic stainless steel were investigated.The purpose of our study is to develop a rapid infiltration rate surface treatment process,and prevent the reduction of the corrosion resistance of austenitic stainless steel in the meantime.A variety methods were used to analyze the treated samples,such as Leica microscope and scanning electron microscope?SEM?,X-ray diffraction?XRD?,3D surface topography analyzer,hardness tester,ball disc friction and wear tester,electrochemical workstation instrument.The morphology,composition,mechanical properties and corrosion resistance of samples were investigated,respectively.Besides,the mechanical properties of the samples were tested and analyzed by microhardness tester,micro-nano comprehensive mechanical system.The experimental results show that:1.Under the condition of hollow cathode auxiliary,high-efficiency nitriding was obtained with a nitriding speed of 17.37?m/h.The highest micro-hardness of the surface is 1608.79HV_0.05.With different parameters,different layer thickness,microstructure,and surface topography can be controlled.2.when the ratio of nitrogen to hydrogen is controlled from 4:1 to 1:6,the nitrided layer thickness decreases from 13.68?m to 6.84?m in the presence of hydrogen,and the microhardness of surface decreases from 1454.54 HV_0.05 to 1164.10 HV_0.05.Under the load of20 N and wear for 1 h with GCr15,only a few marks of wear and plastic deformation appeared on the morphology of the sample when the ratio of nitrogen to hydrogen is the 4:1,which obtained the best wear resistance.3.After the samples are treated with PN,the main phases of the surface infiltrated layer are?_N,PNC and PNC+PN are mainly?_NC.The higher the contents of C and N exist in the infiltrated layer,the higher value of the lattice parameter of the phase composition is in the layer and the greater the density of the slip band is in the C and N layers.Both of?111?and?200?crystal planes,in accordance with the order of PN,PNC,PNC+PN,the crystal spacing increases gradually.4.Compared with the untreated sample,the wear resistance of 316L austenitic stainless steel is improved by low-temperature nitriding,the friction coefficient decreased from 0.57 to 0.45-0.47 and the grinding mark depth was obviously decreased.The polarization behavior measured in 3.5%NaCl solution shows that the nitriding layer without CrN precipitation helps to improve the corrosion resistance.