Microstructure And Properties Of Plasma Nitrided M50 Steel By Ion Source

In this paper M50 steel is selected to applied for high performance bearings.On the basis of small change of the surface roughness after nitriding,the research purpose at investigating the microstructure and mechanical properties of plasma nitrided layer of M50 steel by anode layer ion source.The plasma characteristics of anode layer ion source are studied,via obtaining the trend of plasma density and energy in different space positions,different plasma supply currents and different furnace pressures by using the Langmuir probe.Microstructure and mechanical properties of plasma nitrided layer of M50 steel by anode layer ion source are analyzed by the influence of nitrided temperature,plasma density of N,the ratio of N and H,Nitrogen pressure and nitrided time.Furthermone the same things are analyzed by glow discharge as a contrast test.The nitrided surface layer’s microhardness,microstructures,friction coefficient,morphologies of the surface and wear scar,elements distributed on the wear scar and the surface roughness characterized by optical microscopy,scanning electron microscope,energy dispersive spectrometer,microhardness tester,universal mechanical tester tribometer and contourgraph.The research shows that the density of the plasma produced by the linear anode ion source raises with the increase of the added current,it reaches the peak at a certain pressure which will reduces the density of the plasma at too high or low pressure.A stable zone with a high plasma density and low energy is used as the placement position of the nitriding sample.The density of the plasma what produced by the glow discharge of the cathode plate increases with the increase of the cathode voltage,and it stay a level of 1015m-3.The density and energy of the plasma are stable in the cathode plate region.The depth of 4 hours nitrided layer obtained by anode layer ion source of M50 steel is up to 40μm,without white compound layer in nitride layer moreover no vein structure in diffusion layer.The hardness and depth of nitrided layer enhanced with the increase of nitriding temperature,ion density and hydrogen content in mixed gas.The surface hardness increases to about 1000HV0.1 while the hardness distribution of the layer decreases slowly.Wear mechanism during dry sliding process is oxidation wear and adhesive wear.The wear rate of the steel surface nitrided is reduced by more than 80% to untreated M50 steel.The surface roughness increased from 0.015μm after polishing to 0.06μm after nitriding.A lower depth of 4 hours nitrided layer obtained by the glow discharge of M50 steel than what made by anode layer ion source,meanwhile the same as hardness distribution and surface hardness.The surface roughness increased from 0.04μm after nitriding.The diffusion of nitrogen promoted with the increase of nitriding temperature,plasma density and nitrogen pressure.