| GCr15 bearing steel is one of the main materials for manufacturing rolling bearings,and rolling bearings are repeatedly subjected to impact loads during normal operation leading to a reduction in their service life.With the rapid development of high-speed rail,precision machine tools and aerospace technology,higher and higher requirements are put forward for high-performance rolling bearings.For GCr15 bearing steel in the use of the process of poor impact resistance and other problems,the study of its impact resistance under impact load is very necessary,and it can further enhance the development of China's high-end equipment manufacturing industry.In this paper,orthogonal tests with different strengthening grinding processing parameters were conducted on GCr15 bearing steel,and then the specimens were subjected to impact tests at high strain rates,and then the change pattern of their impact resistance was analyzed.The main conclusions are as follows.(1)After strengthening grinding processing,the surface layer of GCr15 bearing steel formed a strengthening layer with higher hardness than the substrate,and the hardness along the surface toward the core gradually decreased and finally stabilized;The experimental group was 10?m from the surface,and compared with the blank group,Its hardness was respectively increased by 12.51%,12.91%,17.24%,17.64%,13.31%,16.17%,17.65%,17.87%,16.63%,18.11%,20.25%,18.94%,16.36%,16.87%,18.65%,17.34%;The eleventh group had the largest increase,reaching 940.21HV.In addition,the surface roughness of the specimens gradually increased due to the surface weave-like structure after strengthening grinding.The processing time and injection pressure had a greater effect on it,while the steel ball diameter and injection angle had a smaller effect on it.With the intensification of plastic deformation of the specimen,the thickness of the reinforced layer gradually increased,and the strengthening effect decreases from the surface to the inside;until the thickness reaches 110?m,it tended to stabilize,and reacheed the maximum value of 120?m in the 11th group,in which the strengthening effect was most significant in the area about 30?m from the surface.(2)After strengthening grinding process,the surface of GCr15 bearing steel undergone strong plastic deformation and produced a strengthening layer,forming a large number of irregular surface-like structures,and the more craters,the greater the degree of plastic deformation produced;microstructure consists of a large number of dislocation aggregation and refinement of the grains,the grains cut and wind each other,forming a large number of irregularly distributed dislocations,and its impact resistance was significantly improved;test group dislocation The dislocation density of the test group increased from 2.12×1014m-2(group 1)to 4.84×1015m-2(group 7),and the grain size was also refined from 30?m(group 1)to 4.65?m(group 7),then the impact resistance of group 7 was the best.(3)Compared with the blank group,the dynamic yield strength and ultimate strength of the specimens in the experimental group after strengthening grinding processing were significantly increased,but the former was not as large as the change in the latter,making the difference between the two increasingly large;and with the increased in strain rate,the slope of the true stress-strain curve showed a decreasing trend,with the greatest elevation in group7,which was 2550 MPa and 3692 MPa,respectively,increasing by 51.78%and 34.01%;and the area enclosed by the true stress-strain curve in group 7 is the largest,and the difference between its two strengths was the largest,reflecting that the material could absorb the most energy,and the total absorbed energy and absorbed energy per unit volume were 14.41 J and8.79×108 J,respectively,with an increase of 102.5%and 194.9%,and its impact resistance was the best.(4)As shown by the analysis of range and variance,it could be seen that the impact toughness of GCr15 bearing steel specimens was significantly affected by the injection pressure(P)and injection time(T)in the strengthening grinding process,and the injection angle(?)was more significant,while the diameter of steel balls was not significant,and the order of sensitivity of each parameter was:injection time(T)>injection pressure(P)>injection angle(?)>diameter of steel balls(D).(5)without strengthening grinding process or the effect was not obvious,the impact specimen along 45°direction impact fracture into several pieces;and with the strengthening grinding its impact resistance was increasing,the specimen will be impacted into fragments,froth,etc;when the injection time and injection pressure increased appropriately,higher dislocation density and finer grains could be obtained,its impact resistance was better.(6)The comprehensive analysis showed that the optimal strengthening grinding processing parameters were 10 min of injection time,0.5 MPa of injection pressure,60°of injection angle and 1 mm of steel ball diameter,which have the best impact resistance. |
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