| EA4T alloy steel is a typical low-carbon alloy steel.Because of its good comprehensive mechanical properties,EA4T steel is widely used as high-speed railway axles.Although the high-speed railway axles are subjected to various types of loads during operation,fatigue failure is the main failure mode yet.As one of the most important production processes,heat treatment significantly affects the fatigue characteristics of the material.Therefore,this paper studies the effects of heat treatment process parameters on the microstructure and fatigue characteristics of EA4T materials.The main research content of this article includes the following aspects:(1)The forged EA4T alloy steel was prepared for heat treatment specimens.Quenching temperature,quenching media,and tempering temperature were selected as three heat treatment process parameters.The laser measuring microscope and field emission scanning electron microscope were used to observe the metallographic structure and fatigue fracture morphology.(2)Static tensile tests,rotating bending fatigue tests,and date processing.The mechanical properties of the heat-treated specimens with different heat treatment parameters were tested.As a result,tensile strength,yield strength,and elongation were obtained.The fatigue tests data was sorted out,and the least square method is used for fitting the fatigue S-N curve of the test piece with different heat treatment process parameters.(3)The influence of different heat treatment process parameters on the fatigue life of EA4T steel was analyzed and discussed.From the perspective of basic mechanical properties and microstructure,combined with the fatigue fracture morphology,the effects of different quenching temperature,quenching media,and tempering temperature on the fatigue properties of EA4T materials are revealed.(4)Based on the fatigue fracture mechanism and dislocation theory,combined with the fatigue fracture morphology and metallographic structure,a dislocation model of fatigue crack initiation and fatigue crack propagation was established,which explained the variations of fatigue performance with different heat treatment process parameters.According to the EI-Haddad parameter,the critical crack length with different tempering temperatures are calculated,and the safety zone where the surface scratches and foreign body damage affect the fatigue limit is determined.Using the modified Miner fatigue damage accumulation theory,the fatigue life prediction method of EA4T alloy steel with random load is obtained.The fatigue crack initiation and propagation mechanism of EA4T alloy steel was established,and the fatigue life prediction method with random load was proposed.Based on the above research,it can be concluded that the EA4T alloy steel specimen obtained the best fatigue performance when the quenching temperature is 860℃,the quenching medium is 4.5-5.5%salt solution,and the final tempering temperature is 600℃.According to the analysis of the phase change of the microstructure,the size and uniformity of the grain size,and the fatigue fracture,the reasons for the change of the fatigue characteristics of the specimen with different heat treatment process parameters are explored,which provides a practical reference to obtain the EA4T high-speed spindle steel with superior fatigue performance. |
PDF Full Text Request