| In recent years,the development of subways in China has been rapid,and there has been an urgent demand for subways with large capacity,fast speed,and high comfort.However,due to the frequent braking of subway vehicles,the number of curves on the line,and the small radius of the curve,the requirements for anti-peeling,wear resistance,and anti out of roundness of the wheels are becoming increasingly high.It had become urgent to extend the service life of subway wheels,reduce wheel maintenance costs,and improve train safety.(1)A study was conducted on typical faults of subway wheels in service,and then performance requirements for subway wheels were proposed.By studying the influence of C,Cr and V on the microstructure,strength,toughness,and hardenability of wheel materials through different composition recipe,a high strength and toughness CL60 V subway wheel material composition was designed.(2)The microstructure and content of high strength and toughness CL60 V subway wheel material were predicted using JMat Pro software,and the CCT diagram was simulated.The actual CCT diagram of the wheel material was measured and compared using Gleeble3800 thermal simulation testing machine,so the critical cooling rates of bainite and martensite were obtained.The influence of different cooling rates on the microstructure content and distribution of the wheel material was studied through experiments.(3)The microstructure evolution law of high strength and toughness CL60 V subway wheel material was studied.The microstructure,pearlite layer spacing,ferrite morphology and content of wheel materials studied through comparing two different cooling methods.It was found that the variable water quenching process can effectively eliminate the generation of upper bainite on the wheel tread,and the mechanical properties of the wheel have been significantly improved.(4)The microstructure evolution law of high strength and toughness CL60 V subway wheel material under different quenching temperatures was studied through experiments,and the optimal quenching temperature of the wheel was obtained.Through tempering process experiments,it was found that the wheel material may have tempering brittleness at 400 ℃and 480 ℃,and the optimal tempering process of the wheel was obtained.(5)Through the physical and chemical performance testing of high strength and toughness CL60 V subway wheel material,it was found that the microstructure is extremely fine layer pearlite and block ferrite dispersed at grain boundaries,which increases the hardness at the wear limit of the wheel by 17 HB and the tensile strength by 63 MPa.The uniformity of wheel hardness and microstructure is significantly improved,and good toughness is maintained.Through EBSD metallographic analysis,it was found that the number and proportion of high angle grain boundaries in the wheel material significantly increased,and the microstructure was significantly refined.Through laboratory service performance comparison tests,the wear rate of high strength and toughness CL60 V subway wheels has been reduced by about 41%,the anti rolling contact peeling life has been improved by about 11.7%,and the resistance to thermal and mechanical damage of the wheels has been significantly improved.(6)The strengthening and toughening mechanisms of CL60 V subway wheel material were studied.Through experiments,it was found that alloy elements Cr and V mainly strengthen the wheels through solid solution,fine grain,and precipitation in the wheel.Secondly,through experimental analysis of abnormal fluctuations in the toughness of subway wheels,it was proposed that the difference in individual grain size is an important factor affecting the toughness of the wheels.The grain size of CL60 V subway wheels reaches 12.5,and the wheel structure is significantly refined,with stronger crack propagation resistance and higher toughness.This is the main mechanism for toughening CL60V subway wheel materials. |
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