The Research On The Microstructure And Performance Of High Performance Bearing Steel During Duplex Thermochemical Processing

With the development of aviation and astronautics, the service conditions ofbearing become more complex, the bearing materials faces demand for high speed,Anti-wear and resistance to corrosion. In considering the conservation of resources andin bearing the most important working face is the contact surface，the progress ofsurface hardened is an important development direction of high performance bearingsteel. Bearing steel treated by duplex-thermochemical processing, not only to ensure agood toughness of core, and diffusion layer obtain high abrasion resistance and frictioncertain corrosion resistance. The organizational characteristics of materials greatlyextend the service life of the bearing, thus improving the overall performance of host.In this paper, the microstructure characteristic of the carburized layer, nitrided layer,carbonitrided layer and compositional characteristics were analyzed. The low-carbonCrNiMoV bearing steel was treated by duplex-thermochemical, research on theinfluence of the heat treatment to the microstructure and properties of the steel, themicrostructure evolution of the diffusion layer treated by duplex-thermochemicalprocessing was analyzed, and the friction and wear properties of the surface.The results of the carburizing, nitriding and carbonitriding process show that: themicrostructure and hardness distribution of diffusion layer closely associated with thecomposition of the steel. For the carburizing process, Mo and Cr elements formcarbides to improve the diffusion layer strength. For the nitriding process, Cr, Velements form nitride to improve the strength of the diffusion layer. The low-carbon CrNiMoV bearing steel was chosen the chemical steel for the duplex-thermochemicalprocessing.Based on the microstructure observation of the low carbon CrNiMoV steel afterheat treatment, it shows that: the microstructure are main made of lath martensite, asthe increase of experiment quenching temperature has little effect on the grain size, buthas effect on the degree of carbide solution. The change of tempering temperature doesnot affect the mode of steel fracture, but it affect the width of lath martensite beam andthe size of carbide, thus it affect the material properties.The results of analysis on the infiltrated layer microstructure shows that: the layerorganizations divided into four layers. The outermost layer is a nitride layer thatthickness of6~8μm; carbonitride intermediate layer is a second layer, has a thicknessof0.3mm; third layer is a carbide layer, has a thickness of1.4mm; fourth layer carbideinterlayer. The maximum hardness is1120HV, and the hardness gradient distribution ofthe diffusion layer is gentle.The results of the friction and wear shows that: the sliding velocity impact fatiguewear of the material surface, with the increasing of surface contact stress increasedadhesive wear. Hardness transition from compound layer to the diffusion layer andhigh hardness can be effective resist abrasive wear and fatigue wear. In greaselubrication experiment, layered nitride structure is conducive to oil, thence slowly thewear occurs.