Study On Plasma Diffusion Strengthening Process Of Precise Micro 316 Stainless Steel Internal Gear And Its Application

Precise micro internal gear is an important part for focusing of micro cameras such as mobile phones,computers and drones.However,it has low hardness,poor wear resistance,and is prone to wear,resulting in a decline in imaging quality.Therefore,it must be strengthened.In this paper,316 stainless steel was taken as the research object.In this paper,OM,SEM,LSCM,EPMA,XRD,VSM,microhardness tester,wear testing machine and electrochemical workstation were used to study the effects of three diffusion strengthening processes(PN,PC and PNC)on the microstructure and properties of 316 stainless steel.The optimal strengthening process was obtained and applied to the production of precise micro316 stainless steel internal gear.The specific conclusions are as follows:(1)The effects of PN,PC and PNC processes on the microstructure and properties of 316steel were studied.The most suitable plasma diffusion process is PNC,but the corrosion resistance of 316 stainless steel decreases after treatment.The differences of microstructure,microhardness,brittleness,wear and corrosion resistance and magnetic properties of 316stainless steel under three processes were analyzed.The results show that the surface of PN diffusion layer is mainly?_N phase,and the surface of PC diffusion layer is mainly?_C phase.The inner layer of PNC diffusion layer is?_C layer,and the outer layer is?_N layer.Three processes have improved the wear resistance of 316 stainless steel.The wear resistance of PNC is the best(about 2 times PN and PC),and the brittleness is low.Three processes have reduced the corrosion resistance of 316 stainless steel.The corrosion resistance of PNC samples decreases least.One is because the inner carbon-rich layer can play a protective role in the outer nitrogen-rich layer after erosion,and the other is that PNC forms a uniform diffusion layer,reducing the corrosion of micro batteries.The ferromagnetism of 316 stainless steel is obviously enhanced under PN process.The PC and PNC do not change the magnetic properties of original 316 stainless steel.According to the order of PC,PNC and PN,the lattice expansion increases in turn.Compared with PNC,PN sample shows weaker interaction between Cr and N and slightly larger lattice expansion,but the magnetic properties are significantly enhanced.In this experiment,the main factor inducing paramagnetic to ferromagnetic transition is lattice expansion.The secondary factor that induces the magnetic phase transition is the interaction between Cr and N.The critical value of lattice expansion that causes the magnetic phase transition is between 4.1%and 5.5%.(2)The PNC strengthening process for precise micro 316 stainless steel internal gear was optimized and the optimal PNC process is as follows:temperature 390°C,holding time 6 h.The influence mechanism of treatment temperature and holding time on the microstructure and properties of 316 stainless steel were analyzed.The results show that the diffusion coefficient is exponentially related to temperature.With the increase of temperature,the diffusion coefficient increases and the diffusing rate increases.However,when the temperature exceeds 390°C,Cr N is precipitated in the diffusion layer,and the matrix is poor in chromium,which leads to the decrease of corrosion resistance.The optimized temperature is 390°C.The holding time is proportional to the square of diffusion depth.When the holding time is less than 6 h,the diffusing rate increases rapidly.When the holding time is more than 6h,the excessive accumulation of N and C atoms on the surface restricts the diffusion driving force,and the diffusing rate increases slowly.At the same time,the precipitation of Cr N increases,resulting in the decrease of corrosion resistance.The optimized holding time is 6 h.(3)The production verification of the optimized PNC strengthening process was carried out.According to the optimal process,the thickness of the diffusion layer of precise micro316 stainless steel internal gear is 27?m.The surface hardness is 1108 HV_0.05.The brittleness level is 1.There is no rust after 48 h salt spray test.No obvious hysteresis phenomenon is observed in the room temperature hysteresis curve.The surface properties of gear products under the optimized process meet the technical and production requirements.