The influence of ultrasonic impact on microstructure and properties of rail steel

The ultrasonic impact treatment on U70 rail way steel was carried out under different technology by using HJ-II ultrasonic impact machine. By fixing the output energy and changing the time of impacting from 3 min to 30min, the influence of impact time on microstructure was observed with the scanning electron microscope of 6360LA type, and the hardness of impacted surface was also researched before and after impact treatment. The wear resistance was tested by using M-2000 type wearing machine. The result indicates that the surface strength of rail steel can be improved evidently by using ultrasonic impact treatment. The surface microstructure of the rail steel could be refined and the hardness and wear resistance of impact layer were significantly improved through the ultrasonic impact technology. The longer the impact time, the greater increasing range of hardness and wear resistance will be. Compared to the sample without treatment, its surface hardness was increased 23.6%, 32.9%, 43.1%, 48.1%, respectively, and the wear resistance was also increased 30.6%, 32.7%, 42.9%, 57.1%, respectively, when the impact time was 3, 6, 15, 30min, respectively.