Study On The Improvement Of 50CrVA Leaf Spring Material Performance Based On Cryogenic Treatment Technology

Due to its superior mechanical properties,50 Cr VA plate spring steel is widely used in heavy duty dedicated dumper.With the harshness of working conditions of dumper,the requirements on various properties of 50 Cr VA plate spring steel,especially the fatigue life and strength,are getting higher and higher.In this study,cryogenic treatment technology was introduced before tempering process,and the influences of various factors on rockwell hardness,impact toughness and wear resistance of 50 Cr VA plate spring steel were studied by designing orthogonal tests with comprehensive consideration of cryogenic treatment temperature,cooling rate,cooling time and number of cryogenic times.A group of optimal technology group was selected.Under this group of technology conditions,the tensile test and the fatigue test under the axial alternating load were carried out on the material,and the tensile strength,yield strength and fatigue life of 5ocrva leaf spring material were measured.The experimental results show that the Rockwell hardness,wear resistance,impact toughness and fatigue life are obviously improved by introducing cryogenic treatment before the conventional heat treatment tempering process.In this paper,SEM tests were carried out on cryogenic and uncryogenic specimens,and the metallographic structure was analyzed.The fracture mechanism of fatigue and impact specimens was obtained by analyzing the fracture of fatigue and impact specimens at both macroscopic and microscopic levels.The main conclusions are as follows:(1)Group 3(cooling rate of 1 ℃ / min,cryogenic temperature of-196 ℃,the cooling time of 24 h,cryogenic number of 3)for the cryogenic processing orthogonal experiment the best technology of the group,in the group under the test conditions,the precipitation of lower bainite and martensite uniform distribution,size,and residual austenite content rarely,impact toughness relative control group increased by 3.97%,hardness change little.(2)After cryogenic treatment and impact test,the fracture mechanism of 50 Cr VA plate spring steel is dimple fracture,which belongs to ductile fracture.(3)Through range analysis,when impact toughness is the main research object,the order of the influence proportion of the key factors of cryogenic treatment is: the number of cryogenic times > the cooling time > the cooling speed > the cryogenic temperature.Theorder of proportion of the influence on the wear amount of 50 Cr VA plate spring steel is: the cryogenic temperature > thee cryogenic times > the cooling time > the cooling speed.(4)After cryogenic treatment,the fatigue life of 50 Cr VA plate spring steel is relatively compared with that of the samples in the conventional process group.Under the same stress level,the fatigue life of 50 Cr VA plate spring steel is significantly improved after cryogenic treatment.