Study On Near Surface Properties Of GCr15 Bearing Ring Under Hard Cutting Process

Bearing is one of the most important basic mechanical parts,they are widely used in industrial sectors,its quality directly determines the level of reliability of the mechanical equipment,the size of the accuracy,the performance of the quality of life and the length of service life.Using the CBN/PCBN ceramic cutting tool of hard dry cutting technology is gradually regarded as alternative coarse,fine cars,grinding, even or grinding based ultra fine grinding of precision,it is one of high efficiency and low cost and clean green processing mainstream technology. In this paper,by using the GCr15 bearing(HRC62~64) hard machining and the near surface properties of the bearing as the research object,based on the use of hard cutting of the bearing rings on the near surface properties of bearing rings were analyzed.This paper is mainly in the following aspects:(1)By means of different heat treatment processes with electrolytic extraction methods,the preparation that could meet the requirements of sample features(uniformity, stability and temperature stability) of the residual austenite in the reference sample, to verify the method and technology of the residual austenite reference samples of generality. Austenite content of inner and outer circle bearing near the surface was in the range of 1% ~ 2.5%.(2)Through rating and observing the ball body and the microstructure of GCr15 bearing ring on the annealed,rating and observing the carbide,microstructure and grain size of hard cutting bearing, and analyzing microstructure of the surface of the channel and 1mm from the surface of the channel,the results show that annealed bearing ring microstructure was ball body and punctate spheroidizing + ferrite and carbides distribution in the ferrite matrix;After quenching and tempering for bearing ferrule,the microstructure was cryptocrystalline martensite + fine acicular martensite + diffusion distribution of granular carbides and a very small amount of residual austenite,grain was fine and the organization was more uniform; bearing microstructure along the depth had no significant changes, the carbide in bearing rings had showed a slight zonal distribution of the trend.(3)Through the groove of GCr15 bearing race for the near surface residual stress distribution measurement,the results show that the use of hard cutting process could form a larger residual compressive stress on the surface of the bearing groove,and with the increase of the depth, the residual compressive stress force would decrease.The maximum compressive stress was about-700 MPa, and the stress layer depth is 60~80?m.By reducing the measurement of corrosion layer depth,could more test the residual stress distribution. The results showed that state hard cutting process in bearing raceway times at the surface residual pressure stress formed spoon type stress distribution curve that was different from the grinding process.The incision bearing rings were unable to obtain accurate test results for bearing ferrule near surface residual, due to the release of residual stress,Complete rings should be applied in the measurement.( 4) Through the bearing ring channel place for measuring microhardness gradient,the results showed that the bearing ring hardness value was between 765 ~ 781 HV,about 62.5 ~ 63.3HRC,bearing ring hardness value along the depth had no obvious regular change.Testing the surface microstructure of bearing channel,you can see law and neat cutting traces. After hard machining, bearing ring channel roughness was about 0.108?m.(5)Through measuring the near surface properties of the precision FAG bearings,including nano hardness, surface morphology,nearly surface residual stress distribution,the content of retained austenite and surface rough degree of performance,as compared with the test processing bearing,the results showed the microstructure of FAG bearing was finer and carbide distribution was more uniform, and the microstructure was better than that of domestic hard bearing. The hardness of FAG grinding bearing was less than that of domestic hard bearing. FAG bearings had a small amount of rough scratches, scratch width were about 2. FAG bearing rings near surface were compressive residual stress, the maximum compressive stress was about-550 MPa, the compressive stress depth was 30?m.(6)The microstructure, hardness, surface roughness and residual austenite content of hard cutting bearing ring could meet and even better than the requirements of the standard,basically could be able to reach the level of foreign advanced precision grinding bearing(FAG bearing),even the size and distribution of the residual stress in the near surface layer is superior to that in foreign advanced precision grinding bearing,this showed that the hard state cutting technology would have a very broad development prospects in the manufacture of precision bearings.