Research On Microstructure And Dimensional Stability Of Bearing Steel For High-precision Bearings

As the key components of the core strategy such as precision machine tools,aero engines,the accuracy maintenance of precision bearings seriously restricts the self-development of precision bearings.The microstructure and dimensional stability of the bearing steel,which is closely related to the manufacturing process,is the main factor leading to the loss of precision bearing accuracy.Confronted with the key technological challenge to improve precision stability of main bearing,the prediction and control of microstructure and dimensional stability of bearing steel is a critical scientific problem to be explored and solved urgently for the independent development of high-precision bearingsIn the dissertation,the microstructure and dimensional stability of bearing steel for high-precision bearings were studied in theories and experiments systematically.The quantitative rules of microstructural evolution during cold deformation,quenching and tempering were studied.The relationship between microstructural transformation during aging and macroscopic dimensional change was revealed.The prediction models for microstructural stability and dimensional stability of GCr15 bearing steel after aging were established.The main research contents include:(1)The spheroidising annealed GCr15 bearing steels were taken as the object.The work hardening behavior and microstructure evolution of spheroidising annealed GCr15 bearing steel during room temperature tension were analyzed.According to the work hardening model,the relationship between stress-strain relationship and dislocation evolution during uniform plastic deformation stage was discussed.The influence of dislocation density on deformation energy storage was analyzed,as well.(2)The spheroidising annealed GCr15 bearing steels with different cold deformation degree were taken as the object.The thermal expansion behavior of GCr15 bearing steel during continuous heating was analyzed by thermal simulation experiment.The austenite transformation kinetics curve was obtained by lever method.Based on JMAK model and nucleation-growth-impingement solid phase transformation analytical model,the austenite transformation behavior of bearing steel was studied,and the key factors affecting the austenitizing dynamic behavior of bearing steel were analyzed.Based on the thermal expansion curve,austenite transformation kinetics and crystallography,a physical and mathematical model for the microstructure evolution of GCr15 bearing steel during the whole heating-quenching process was established and verified by quantitative metallographic method.The key factors affecting the quenching structure state were revealed.(3)GCr15 bearing steel with different degree of cold deformation and quenching process was taken as the research object.The transformation behavior of retained austenite during tempering was thermodynamic analyzed.Microstructure evolution of GCr15 Bearing Steel during continuous-heating tempering was analyzed by Kissinger method and Isoconversional method,respectively.Subsequently,isothermal tempering kinetic parameters were solved basing on isoconversional method and fitted in a JMAK type equation and verified by microhardness test.The effect of cold deformation and quenching on the transformation of tempered structure was revealed.(4)GCr15 bearing steel after different quenched and tempered process was studied.Based on the tempering kinetics and virtual time,a prediction model for the microstructural stability in bearing steel was established and verified by XRD test.The influence of cold deformation and heat treatment parameters on the microstructure stability was studied.Subsequently,based on the crystallography,tempering kinetics and virtual time,a prediction model for the dimensional stability of GCr15 bearing steel after aging was established and verified by aging test under constant temperature.The influence of cold deformation and heat treatment parameters on the microstructure stability was revealed.(5)According to all the research above,the cold deformation,heat treatment process parameters of GCr15 bearing steel were preliminarily optimized by means of response surface method,and then the results of response surface analysis were quadratically optimized by using dimensional stability prediction model of bearing matrix steel.According to the results of the second optimization,the corresponding deformation,heat treatment experiments and verifiable experiments were carried out.The mechanical properties and dimensional stability of the experimental results basically met the expectations.The research results provided reference for optimizing the forming process of bearing matrix,controlling and improving the microstructural and dimensional stability of steel used for precision bearings.The research results in this dissertation enrich the theoretical system of bearing matrix manufacturing method with deformation-phase transformation synergy,provided reference for optimizing the forming process of bearing matrix,controlling and improving the microstructural and dimensional stability of steel.