| Carburizing bearing steel is actually high quality low carbon alloy steel. After bearing parts carburized, the surface has high strength and the core has good toughness to bear a larger impact load. Low-carbon CrNiMo carburizing bearing steel which smelted by double vacuum (VIM+VAR) as experimental material was adopt. Through changing the quenching,temper temperatures, the heat treatment process which has the optimum toughness matching the microstructure’s performance have been determined. Through OM,SEM, TEM and thermal simulation methods,the microstructure characteristic of the core and carburizing bearing steel’s carburized layer and dynamic recrystallization were analyzed, and found the reason why strength-toughness increased; Based on friction and wear test examing, the wear resistance of carburized bearing steel was studied and the main wear failure mechanism under different conditions were preliminary summarized.Based on the microstructure observation of low carbon CrNiMo carburizing bearing steel after heat treatment,it shows that the microstructure are main made of lath martensite,a little of residual austenite and carbides. With the increase of quenching temperature, grains and carbides grow up and disperse, fracture toughness nests are from small to big, and the higher tempering temperature, the lath martensite decomposes gradually, grain boundary solution disappear, toughening nests become small.When higher temperature tempering, the second phase grows up and carbides along the grain boundary get into a linear distributio. For best strength to match the performance of the microsrtucture and austenitizing fully, and to the best carburizing case process, the final heat treatment process was made that:heating1hour at910℃and then oil quenching,at last for2hours of180℃low temperature tempering and air cooling, its impact energy is170J and the tensile strength is1260Mpa.Thermal deformation stress and strain regularity of low carbon CrNiMo carburizing bearing steel shows that:high deformation temperature, low strain rate and large deformation are conducive to the occurrence of dynamic recrystallization,the fine recrystallized grains were abtained at1050℃,50%deformation and strain rate Is-1in this experiment,and the average grain size is 14.97μm; The activation energy of low carbon CrNiMo carburized bearing steel decreases slowly when deformation larger than30%,it is deduced to436.016kJ/mol in50%deformation;The material has reached to the the dynamic recrystallization thermodynamic condition in900℃,1s-1,50%deformation,and the critical static recrystallization time is5min after continue heated. The experimental results are also matched to the hot working map which made by the relationship between strain and stress.Based on the research of low carbon CrNiMo carburizing bearing steel ooze layer microstructure and the friction and wear properties,it shows that the surface hardness of experimental steels after910℃quenching and180℃low temperature tempering are all more than750HV.The microstructure are composed of high carbon acicular martensite, carbide(M23C6, M6C or MC) and5.6%retained austenite. With the increase of infiltration layer thickness carbide in the martensitic becomes small. When permeability layer measured by hardness method is less than1.6mm, HV is greater than550HV, and the core hardness value is about400HV, it means the carburizing layer is thicker than1.6mm.Friction and wear experiments of Low-carbon CrNiMo carburized bearing steel were carried out under no lubrication and grease lubrication, respectively for three kinds of point, line and face contact. Look from the coefficient of friction, carburizing bearing steel’s average friction coefficients of point, line and face contact were0.50,0.65,0.55under no lubricated; From the point of view of wear mechanism, point friction was mainly adhesion wear under no friction lubrication accompanied by abrasive wear and line friction was given priority to with abrasive wear, surface friction was mainly abrasive wear and adhesive wear. Average friction coefficient of point, line and face were0.09,0.10,0.11under lubricated, the wear mechanism of the point friction was mainly in the form of fatigue wear,and fatigue wear happened on both ends of the line friction,but abrasive wear in the core, the surface frictionwas mainly abrasive wear and tear. Line face wear weight was more0.002g under no lubrication wear, point wear was less0.001g under nolubrication.The grease lubrication under the wear condition of point, line and plane were less than0.0005g. No lubrication friction wear debris was iron oxide by energy spectrum and color determination, lubrication friction wear debris was the iron substrate. Grinding crack depth of point, line and face were51.4mu m,28.2mu m and28.2mu m under Non-lubricated wear, but the grinding crack depth was more shallow under grease wear, which indicates that the friction experiments of infiltration layer coun’t cause a serious damage to surface, the experimental steel possesses higher wear resistance. |
PDF Full Text Request