Study On The Tempering Of High Carbon Bearing Steel And The Wear Behavior

In this paper,different low temperature tempering heat treatments were carried out for typical high carbon bearing steel,and the microstructure evolution,mechanical properties and fatigue wear resistance of tempered martensite were controlled by controlling the precipitation of carbides during tempering.With the aid of field emission scanning electron microscope(SEM),electron backscatter diffraction,(EBSD),X-ray diffractometer(XRD),fatigue wear tester and other testing methods,the fatigue wear experiments of high carbon bearing steel were carried out systematically,and the microstructure and properties of plastic deformation layers under different high cycle wear cycles were analyzed and characterized from the structural evolution of wear subsurface layer,post-wear hardening and wear weight loss as a starting point.To explore the evolution law of microstructure in the deformed layer and the mechanism of carbide decomposition and tempering in the subsurface area to improve the wear resistance of the material.The research of this paper is of positive significance to realize the optimization of heat treatment process,regulate the matching of microstructure strength and toughness of high carbon bearing steel,and prolong the service life of workpieces.The main conclusions are as follows(1)The microstructure of quenched high carbon steel is typical martensite,accompanied by retained austenite and insoluble carbide;tempering treatment with different processes can promote the decomposition of a large number of retained austenite in microstructure.The tempering treatment of different processes can promote the decomposition of a large number of retained austenite in the microstructure and precipitate tempered carbides(ε,η,θ);During tempering at 170 °C,fine ε-carbides precipitate in a coherent manner.With the increase of tempering temperature,the ε-carbide gradually changes to θ-carbide,and the coherent relationship disappears with the growth of carbides,and the precipitated tempered carbides are finer when tempered at 230 °C.With the precipitation of carbides in the tempering process,the solid solution strengthening of the matrix weakens,the hardness decreases gradually,the ultimate compressive strength decreases,and the compression ratio increases.The best ratio of strength and plasticity can be obtained by quenching and tempering at 230 °C: 6.84GPa·%(GCr15Si Mn)and 5.71GPa·%(GCr15).At the same time,due to the inhibitory effect of Si and Mn on carbide precipitation,the hardness and ultimate compressive strength of GCr15 Si Mn are higher than those of GCr15 after quenching and tempering.(2)The wear process of the samples under different heat treatment conditions is mainly local spalling failure.In the process of wear,plastic deformation occurs on the contact surface,forming a grain refinement layer with layered structure,and the thickness of layered structure increases with the increase of cycle times.The samples tempered at 230 °C for 24 h showed good wear resistance in the wear test.Due to the large number of fine and dispersed nano-sized carbides in the structure and close bonding with the matrix,it is not easy to become the source of cracks and reduce the spalling and weight loss caused by crack propagation.(3)The mechanism of mechanically induced carbide decomposition is discussed.the plastic flow of the matrix is hindered by spherical carbide,which leads to the increase of local strain of the matrix,the formation point of dislocation at the interface and the accumulation of a large number of dislocations.When the stress concentration exceeds the critical shear strength of the carbide,the slip occurs,the interface step is produced,and the carbide is divided.Finally,a complete carbide particle is divided into several small carbides.Large-size carbide particles are easy to decompose and redissolve into the matrix in the process of wear.