Study On Rotary Bending Fatigue Properties Of GCr15 Bearing Steel

GCr15 bearing steels with four different smelting processes,LF+RH/VD,ESR,VAR and VIM+VAR,were selected as test materials and characterized by rotary bending fatigue test and ASPEX SEM.High cycle mechanical fatigue test of GCr15 bearing steel prepared by four processes was carried out.It was found that under 10~7 fatigue life conditions,VAR bearing steel bending fatigue strength reached 1131 MPa,followed by VIM+VAR and ESR processes,which were 1087 and 1085 MPa,respectively.The lowest steel bending fatigue strength of GCr15 bearing prepared by vacuum degassing was 1000MPa.and 1029 MPa(new heat treatment process).Comparing with the mechanical data,it is found that there is a good positive correlation between fatigue strength and tensile limit.The scanning electron microscope was used to characterize and analyze the fatigue fracture surface.The results show that the average sizes of sample initiation inclusions prepared by vacuum degassing process are 27.1 and 24.67 microns,however,the average inclusion sizes leading to ESR,VAR and VIM+VAR steel fatigue fracture are 13.3,13.83 and 13.89μm respectively.Based on the study of the relationship between the characteristic parameters of the whole fatigue process,such as crack initiation core inclusions,crack propagation fish eye and instantaneous fracture zone,and the bending fatigue strength and life,it is found that the size and distribution of large particle inclusions(DS)are the key factors affecting the bending fatigue strength and life of bearing steel.At the same time,it is found that the fatigue fracture of electroslag bearing steel caused by TiN as the crack source accounts for about 50%of the total number of specimens,while most of the other specimens are composed of Al-Ca-O-S-Mn composite spherical inclusion.ASPEX scanning electron microscope was used to detect inclusion in four groups of test steels and large size inclusion.In the whole inclusion test,the inclusion content of GCr15 bearing steel prepared by vacuum degassing per unit area is higher than that of the other three groups of samples.The inclusion amount in ESR steel is the largest,but the proportion of small inclusion size is higher.The number and size of inclusion in VAR and VIM+VAR process are better than those in the other two groups.For large-size inclusion detection,24 maximum inclusion searching scans were carried out on bearing steel prepared by each process,and the results were brought into Weibull distribution coordinate paper.It was found that the maximum inclusion distribution in bearing steel matrix prepared by vacuum degassing was higher than that of the other three groups of samples,which corresponded well to its fatigue fracture inclusion.In order to compare the relationship between fatigue fracture and ASPEX inclusion,the extreme value statistical method was used to calculate the inclusion of fatigue fracture and ASPEX inclusion,respectively.It was found that the distribution of inclusion in the whole size region was basically the same by the two methods.The inclusion size and dispersion of vacuum degassing samples are larger than those of the other three processes.In the maximum inclusion prediction of extremum statistical method,the fitting function of Weibull distribution does not converge and fluctuates with the dispersion of experimental data to a great extent,the prediction results only have reference significance in combination with inclusion control technology under actual smelting conditions.