Effect Of Surface Ultrasonic Rolling On Surface Properties Of Axles And Its Mechanism

With the development of China's railway industry and the improvement of train speed,it is more and more important to ensure the safety of the train.The axle of high-speed emus needs to bear several million times of alternating load during the service period,and the stress situation is very complex.About 2/3 of axle failure accidents are caused by fatigue crack.The surface is the main area where the fatigue crack occurs on the axle.This paper mainly studies the influence of surface ultrasonic rolling process number and different process on the surface performance of axle,and discusses the strengthening mechanism of surface ultrasonic rolling of axle.Ultrasonic rolling processing equipment is used to perform surface ultrasonic rolling treatment for EA4T axle with 9 different process parameters after turning.Through the analysis of surface morphology,microhardness,residual stress and microstructure,the orthogonal test is conducted.Finally,the effects of different factors on different surface properties are obtained.Turning,grinding,rolling and ultrasonic rolling are carried out on the position of the axle arc to measure the surface roughness,microhardness,residual stress on the surface and observe the surface microstructure.The characteristics of different surface strengthening processes are compared and analyzed.The strengthening effect of surface ultrasonic rolling on axle material is compared by rotary bending fatigue test.EA4T axle steel samples were treated by ultrasonic rolling with different rolling passes,and the strengthening mechanism is analyzed.The results show that the optimum process parameters obtained in this test range are spindle speed of 10 r/min,feed rate of 0.1 mm/r,and rolling pressure of 3000 N.The surface of the axle after ultrasonic rolling treatment is very smooth,the surface roughness value(Ra)can be reduced to 0.041 ?m.As opposed to turning,grinding,and rolling,surface ultrasonic rolling increases the surface hardness of the axle to a maximum depth of up to 500 ?m.After grinding,rolling and ultrasonic rolling treatment,the residual tensile stress after turning can be transformed into residual compressive stress.The axial residual stress after surface ultrasonic rolling treatment has the most obvious change effect,and the maximum residual compressive stress is 799 MPa.Through fatigue test,it is concluded that ultrasonic rolling treatment on the surface can significantly improve the fatigue life of samples,and some samples reach 1×107 r without fatigue fracture.After surface ultrasonic rolling treatment,the surface of the axle forms a certain depth of plastic deformation layer,and a large number of dislocations appear in the surface grain,and the surface grain can be refined to the nanometer level,the axle surface strength is significantly improved,and showing excellent surface properties.