Research On The Strengthening Mechanism And Fretting Wear And Rotating Bending Fatigue Properties Of Ultrasonic Rolling Of New Steel For Shaft

Drive shaft of gearbox is one of the key parts of high-speed and heavy-load vehicles,which has a bad working environment and complex stress condition.It usually fails with wear and fatigue,most of which start from surface.25Cr Ni2Mo V steel is a new type of high-speed and heavy-load vehicle drive shaft steel of gearbox.In order to improve the surface performance and wear resistance of the parts,ultrasonic surface rolling process was applied to25Cr Ni2Mo V steel,which was of great significance to improve the wear resistance and fatigue performance of the steel and extend its service life.By the way of experiment,the effect of rolling parameters on the surface strengthening of 25Cr Ni2Mo V steel was studied.The strengthening mechanism of ultrasonic surface rolling of shaft steel was analyzed.The results showed that the most significant surface grain refinement,the minimum surface roughness,the maximum surface microhardness and the maximum surface residual compressive stress were obtained at the rolling load,ultrasonic frequency and ultrasonic amplitude respectively in 1200N-30k Hz-12?m,800N-25k Hz-6?m,1400N-30k Hz-8?m and 1200N-25k Hz-8?m.The dynamic simulation of ultrasonic surface rolling was carried out by using ABAQUS,obtaining the variation law of surface performance with the rolling parameters.The results showed that ultrasonic surface rolling effectively improved the energy and processing deformation of the material surface,and produced large residual compressive stress.The residual compressive stress increased first and then decreased with the increase of depth,the maximum residual compressive stress value was 906?1066MPa between 0.135?0.212mm from the top surface.Rolling load,ultrasonic frequency and ultrasonic amplitude respectively in 1200N-25k Hz-8?m obtained the simulation value of the optimal surface residual stress.The error between the simulation value of surface residual stress and the experiment value was within 13%,indicating that the ultrasonic surface rolling model has better accuracy.According to the results of experiment and simulation study of ultrasonic surface rolling,the fretting wear properties of 25Cr Ni2Mo V steel under different rolling parameters were studied.The rolling parameters in rolling load 1200N,ultrasonic frequency 25k Hz and ultrasonic amplitude 8?m obtained the best wear resistance,which was shown as the average friction coefficient decreased by 17.86%,the wear volume decreased by 39.48%,and the wear mechanism changed from adhesive wear of the untreated specimen to abrasive wear.Based on the results of ultrasonic surface rolling experiment and simulation study,the rotary bending fatigue properties of 25Cr Ni2Mo V steel under different rolling parameters were analyzed.The fatigue strength limit of the untreated specimen was 840 MPa at 10~7cycles.After ultrasonic surface rolling,the fatigue strength limit of the specimen increased.The specimens with the rolling parameters in the optimal surface residual compressive stress(rolling load 1200N,ultrasonic frequency 25k Hz,ultrasonic amplitude 8?m)had the optimal fatigue performance,its fatigue strength limit is 970 MPa.It showed that ultrasonic surface rolling strengthening technology can effectively improve fatigue life of 25Cr Ni2Mo V steel.The fracture morphology after experiment was divided into crack initiation region,crack propagation region and crack fracture region.The cracks of the untreated specimen originated on the surface of the specimen,while the cracks of the treated specimen originated on the sub surface.After ultrasonic surface rolling,the structure of the crack propagation region and the dimple size of the crack fracture region were smaller.