Research about the Effect of Ultrasonic Impact on the Fatigue Properties of Cruciform Joints of 16MnR Steel

Surface impact treatment was carried out on the cruciform joint weldment of 16MnR steel by using the HJ-II-type ultrasonic impact machine.The ultrasonic impact current is 1.2 A,the impact amplitude is 30?m and ultrasonic impacting time is 30 and 60 min,respectively.Fatigue experiments were carried out for both treated specimen and un-treated specimen by using EHF-EM200K2-070-1A fatigue testing machine.The fatigue fractures were observed with the scanning electron microscope of 6360LA type and the microstructure of ultrasonic impact treating surface layer was analyzed by using high resolution transmission electron microscope of JEM-2100 type.The experimental results show that the microstructure of ultrasonic impact surface layer has been successfully nanocrystallized.The fatigue life of welded cruciform joints of 16MnR steel can be significantly improved through the ultrasonic impact treatment.The main reasons are that the ultrasonic impact treating can reduces the stress concentration in the weld toe,decrease the tensile stress,and even change to compressive stress in the weldment,the grain size in the welded joint can be refined.The longer the impact time,the greater increasing range of fatigue life will be.Compared to the sample without treatment,its fatigue life was increased 210.37%,362.48%,respectively,when the impact time was 30,60 min,respectively.