| The new bainitic bearing steels,GCr15 SiMoAl and GCr15Si1 Mo,have been studied in this paper.The microstructure,fracture morphology,phase composition and surface morphology were observed and measured by optical microscope,scanning electron microscope,Transmission electron microscopy,X-ray diffraction and optical profiler.These subjects are investigated: effect of heat treatment processes on the microstructure and mechanical properties of the steels;influnce of hydrogen on compressive deformation behaviors of GCr15 SiMoAl steel and contact fatigue properties of GCr15Si1 Mo bearing steel;wear behaviors of GCr15Si1 Mo bearing steel with different microstructures.Compressive deformation behaviors of GCr15 SiMoAl bearing steel before and after charging hydrogen processes on the have been investigated by Gleeble 3500 thermal-mechanical testing system,and then the results are compared with that of the traditional GCr15 bearing steel.Results show that the mixed microstructures consisting of bainitic ferrite,retained austenite and martensite obtained after isothermal transformation for 0.5 h in GCr15 SiMoAl bearing steel exhibits the excellent comprehensive compressive deformation property.With the increase in isothermal time,the volume fraction of bainite ferrite increases.The compressive strength gradually reduces,while the compression ratio increases firstly and then decreases.The performances of GCr15 SiMoAl bearing steel after isothermal transformation and oil quenching processes are better than that of traditional GCr15 bearing steel obtained after oil quenching.Hydrogen has negligible influence on compressive strength of the bearing steel.However,the addition of hydrogen deteriorates the plasticity of the bearing steel significantly due to the fact that hydrogen promotes strain induced transformation from retained austenite to martensite.Fatigue tests before and after charging hydrogen were investigated by the TLP-1 fatigue testing machine.The results show that the addition of hydrogen in steel promotes the formation and propagation of cracks,resulting in the reduction of fatigue life of GCr15Si1 Mo bainite bearing steel.The full bainitic microstructure exhibits the optimal wear resistance,which is comparative to the martensitic steel obtained by quenching with high hardness.Besides,the wear resistance of the bainite steel after tempering treatment is obviously better than that of steel without tempering.Moreover,the samples containing undissolved carbides are better than that without carbides.The longitudinal sections after wear show serious deformation zones,including serious deformation area,rheological zone and the organization of serious refinement area.With the increase in the wear time,the microstructures are damaged more seriously.The wear resistance of the steel can be effectively improved by the strain induced transformation from retained austenite into martensite during the wear process.As the wear time is prolonged,the worn depth at the same location and the average roughness increases,which make the damage level of the worn surface more seriously.In the meanwhile,the microstructure of worn surface is refined,and the carbides are redissolved into the matrix during wear process. |
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