The Study On Vacuum Carbon-nitrogen Compound Infiltration Process And Permeability Characteristics Of 20CrMnTi Steel

Preparation of carburizing layer by vacuum pulse carburizing and vacuum induction carburizing,ion nitriding and vacuum induction nitriding to produce nitriding layer,vacuum pulse carburization +(vacuum impulse nitriding,vacuum induction nitriding,ion nitriding),these three methods and vacuum induction carbonitriding method were used to prepare carbon-nitrogen composite strengthening layer.The X-ray diffractometer,microscope,scanning electron microscope,energy spectrometer,EBSD,microhardness tester and micro-scratch tester were used to analyze the penetration layer,the phase,structure,cross-section element distribution,phase distribution,compactness,micro-hardness gradient,and the delamination brittleness.The results show that: vacuum induction carburizing: under the same carburizing pressure,the surface hardness value is higher than the corresponding surface hardness value of the vacuum pulse carburizing process,the thickness of the permeation layer is also higher than the corresponding vacuum pulse carburizing process,and the wear resistance is Better than vacuum pulse carburizing,with a wear rate of 6.27E-07 cm3/min·N at-70 k Pa,a carburized layer of 400-500 ?m can be obtained in 15 min,and the depth of the penetration layer reaches 1 after 1 h Mm,hardness of the penetration layer exceeds 750 HV,excellent carburizing dynamics.The vacuum induction carburizing process is controlled by "surface adsorption" and "inside diffusion".And the "surface adsorption" is a relatively major controlling factor.When the carburizing time is less than 125 minutes,"surface adsorption" is the main speed control factor,while the carburizing time is greater than 125 minutes,the internal diffusion becomes the main speed control link.Vacuum induction nitriding: the higher the temperature,the lower the hardness of the nitriding surface.when the temperature is 500,530 and 560 °C,inductive nitriding and ion nitriding have similar phase,microstructure,microhardness gradient and effective nitriding layer thickness and similar Wear resistance,surface nitrided layer of induction nitriding has a higher surface hardness value.However,the porous structure is not dense in the outermost layer of 1~2 ?m.Nitriding strengthening layer of 300 ?m or more can be obtained in vacuum induction nitriding within 1 h.The gas pressure has little effect on the thickness of the nitriding layer,with the seepage.Nitrogen gas pressure increases,the thickness of the penetrating layer increases slightly,but when the pressure of the nitrogen gas is too high,the brittleness of the nitrided layer increases.The bright white layer prepared by the first carburizing ion nitriding process is the thickest and the relative content of nitrogen is the highest,which is almost twice that of single ion nitriding.The nitrogen atom has greater solubility in austenite,and is formed after carburizing and quenching.Retained austenite contributes to the adsorption of active nitrogen atoms,and lattice distortion in the formation of martensite produces many voids,which favors the diffusion of nitrogen atoms and gives it a thicker seepage layer.The bright white layer is mainly strengthened by the carbide Fe4 N.To make up for the lack of surface hardness.Vacuum inductive carbonitriding with different gas pressures has effectively improved the surface friction properties of 20 Cr Mn Ti steel.When the pressure is-25 k Pa,the wear resistance is the best,the wear rate is the lowest,and the wear rate is5.32E-07 cm3/ Min·N.