Microstructures And Properties Of The Gradient Layer On 40Cr Surface By Thermal Diffusion Process

Gear is one of the common transmission parts worldwide.In order to prolong its life,it is often required that the materials have wear resistance,corrosion resistance and so on.With the advancement of industrialization,the homogeneous material is difficult to meet the present comprehensive requirements.Using the coating as the working layer of the parts can improve the service life effectively.Thermal diffusion technology can not only produce metallurgical bonding layer on the surface of gear materials,but select one or more diffusion elements according to the property requirements.The layer prepared by thermal diffusion can improve the microstructures and surface properties effectively.This project was supported by the national natural science fund “Performance distribution regulation and service behavior of multi-component thermochemical treatment on FGM coated gear”(code: 51575073).The common gear material 40 Cr was selected as the matrix material,and electromagnetic induction heating was chosen as an alloying method.The purpose of this paper is to improve the comprehensive performance of the 40 Cr steel,study on the microstructures and properties,compare with traditional box type furnace and provide technical reference and theoretical support for the research of gear surface modification technology.The main contents of this paper are as follows:(1)Summarized the surface modification technology of gear.The realization means and the current research status of thermal expansion process were mainly discussed.(2)Chromizing layer was prepared on the substrate of 40 Cr steel by induction heating at different temperatures.The microstructures and properties were characterized,and the corresponding diffusion mechanism of Cr element with the induction heating method was analyzed.(3)Aluminizing layer was prepared by box furnace and induction heating on the 40 Cr steel respectively.The difference of microstructures and properties of aluminizing layer by different heating methods was discussed.(4)The chromaluminizing was prepared by box type furnace and induction heating method.The microstructures and properties of the chromaluminizing layer were compared.The diffusion mechanism and formation mechanism of the elements were also analyzed.The above studies show that,the layer of IHC-1000 sample consists of pearlite and ferrite,while the IHC-1300 layer present the coarse columnar grain.IHC-1000 sample hasthe better binding force and section hardness gradient.The thickness of two layers is similar,which is about 80μm.And both of layers have the property of external hard internal toughness.The aluminizing layer heated by induction furnace is thicker than the layer heated by box type furnace,but it has the poor compactness.The contents of Al and Fe in the two kinds of aluminizing layers change contrarily,and the box type aluminizing layer has the better section hardness,corrosion resistance and surface roughness.The chromaluminizing layer heated by induction furnace has the better microstructures and properties.It is thicker which is about 362μm,and the layer is composed of three regions,respectively the surface columnar crystal area,intermediate fine pearlite area and long strip crystal area.The layer of box type furnace is poor,the chromium element is suppressed during the diffusion process,and the thickness of the layer is only 20μm.However,both two kinds of chromaluminizing layer can improve the corrosion resistance in Na Cl aqueous solution and(H2SO4,Na2SO4)aqueous solution.The corrosion resistance of the induction-chromaluminized sample is about 166 times of the matrix,and is about 4 times of the box type chromaluminizing sample.In the acid medium,the corrosion resistance is about 77 times than that of the matrix and about 4 times than that of box type chromaluminizing sample.The paper has the following innovations:(1)The chromizing layer was successfully prepared by powder embedding with induction heating.It was found that the diffusion effect of Cr element was different with the increase of temperature,and the diffusing mechanism of different temperature was analyzed.(2)The embedding aluminizing process was realized by box type furnace and induction heating furnace.The difference of microstructures and properties of aluminizing layer prepared by two heating equipments were systematically studied.(3)The chromaluminizing was realized by induction heating.The thickness and performance of the chromaluminizing layer were greatly improved compared with the box type furnace heating.And the difference of the formation mechanism of different process has been discussed in detail.