Study On Electron Beam Alloying Process And Properties Of40Cr Surface

Gear as a kind of basic mechanical transmission parts is widely used, with thecontinuous development of science and technology level, the integrated performance of thegear surface is becoming more and more demanding. As a kind of commonly used gearmaterials,40Cr materials is widely used, but conventional heat treatment methods havebeen unable to meet the surface requirements of high strength and high precision. Becauseof this, the new surface treatment technology which has the characteristics thatenvironmental protection, high energy utilization and achieving high surface strength withthe condition of the workpiece accuracy unchanged, has been widely researched anddeveloped.This article originates from a part of the open fund project of ministry of educationkey laboratory of manufacture and test techniques for automobile parts, named "Study onelectron beam surface alloying process and rolling contact fatigue performance of gearsurface". This paper chose hard chromium plating as electron beam alloying pre-coating,discussed the influence of the macro and micro organizational structure, microscopicstrengthening mechanism and surface properties of40Cr treated by electron beam alloying,summarized the relationship and the law between the electron beam surface alloyingprocess parameters and properties, provided a basis for obtaining the electron beamalloying process which made the gear surface comprehensive performance best. Accordingto the relationship between the pre-coating thickness and the depth of melting layer causedby electron beam irradiation, this paper designed two kinds of experiment scheme. For thefirst experiment scheme, pre-coating thickness is greater than the depth of melting layercaused by electron beam irradiation; for the second experiment scheme, it’s an orthogonalexperiment that pre-coating thickness is less than the depth of melting layer. Major workaccomplished in this paper is as follows:(1) Through comparative analysis of two kinds of experiment scheme by means ofoptical microscope, scanning electron microscope (SEM), energy disperse spectroscopy(EDS) and X-ray diffraction, the influence of different electron beam alloying processparameters on surface morphology and microstructure of40Cr was studied.(2) Based on the comprehensive performance testing, such as surface roughness,microhardness, wear resistance and corrosion resistance and so on, the influence law of different electron beam alloying process parameters on the material surface properties wasanalyzed, and the surface strengthening mechanism was discussed at the same time.The results show that: the sample surface treated by scheme1appears the dense mesh"ditches" morphology and a large number of micro cracks, but when the sample surface istreated by scheme2, the "ditches" morphology will not appear and only the micro crackswill present, and when sample is treated by the optimal process parameters of orthogonalexperiment, the micro cracks will disappear; for the sample treated by scheme1, thesurface hardness only has slightly improved and the surface roughness improves a lot, butfor the sample treated by scheme2, the surface hardness will increased by about22%andthe surface roughness will reduced by49%; for the sample treated by scheme2, depth ofthe alloying layer will reach about8μm, accompanied by a new residual austenite phasegenerated at the same time; for the sample treated by scheme2, its wear resistance has agreat improvement and wear weightlessness will reduce by30.8%，but due to the largenumber of melt hole and the manganese sulfide inclusions included in the matrix of40Crerupted to the surface, its corrosion resistant performance is not better than the sampletreated by scheme1. Final results show that the sample surface integrated performancetreated by scheme2is superior to scheme1.