Oversize bearing outer ring early failure reason analysis

A bearing users reflect a set of very large double LieDiao found in the process of using roller bearings bearing outer ring rolling to the premature failure of the present, the set of bearing ring is used for cement grinding roller, poor working conditions. The model data as GCr15SiMn steel, its processing process is: phi 300 mm in the original data into the factory - blanking period of ultrasonic flaw detection to forging forming, the spheroidizing annealing - car processing - heat treatment - detection - grinding - inspection - assembly into the Treasury. Now I stop to its physical and chemical inspection, find out the reason for the failure. 1. The physical and chemical inspection ( 1) Macroscopic examination outer ring by gas cutting sampling, whole raceway surface friction and wear, there were parts with irregular holes, its morphology is shown in figure 1, in addition to this abnormality was not found. Figure 1 outer ring raceway surface, macro ( 2) Chemical composition analyzing external loop to stop sampling, the size is 15 mm * 15 mm * 15 mm, using direct reading spectrometer stop chemical composition analysis, test results are shown in table 1, its chemical composition with GB/T18254 - In 2016 GCr15SiMn specification request. The main chemical composition (table 1 outer ring The mass fraction) （ %） （ 3) Metallographic examination in the first place, low power view. Making the hole site fracture specimens after check, rough visible fracture appearance, shiny grain surface edges, in addition to this, also distribute holes, commonly known as 'tofu' fracture, the fracture morphology as shown in figure 2 a shows. Test of arbitrary section after the macroscopic view, visible appearance has large holes scattered, edge Angle shaped, individual holes bottomless, its exterior appearance is shown in figure 2 b. （ 一) Fracture ( b） Metallographic, macro figure 2 second, metallographic look. Making the hole site section under OLYMPUSGX51 microscope after metallographic specimen view, visible on the cross section has a large number of irregular Angle hole spread, margin with oxidation, individual holes bottomless, its microstructure morphology is shown in figure 3. In figure 3 hole section morphology in the end, sem fracture analysis. For making the hole site after fracture in JMS - 6610 lv look under scanning electron microscopy (sem), visible fracture distribution has a lot of Angle shaped holes, hole part with metal melt morphology, as shown in figure 4. Figure 4 holes microscopic morphology ( 4) Materials and heat treatment after the quality test for making outer vertical and horizontal section metallographic specimen, under optical microscope view, according to the standard GB/T 18254 - And heat treatment standard JB/T 1255-2016 2014 stop assess, test results as shown in table 2 and table 3 respectively, the above test results are agree with specification request. Table 2 outer data quality inspection table 3 outer heat treatment quality testing project supporting austenite organization levels/martensite structure/carbide hardness HRC outer ring 231 mesh/level. 060, 61, 61, 21 ~ 4 or less 2 or less specification values. From 558 to 632. Analyze the discussion on the ferrule macroscopic examination, composition analysis, metallographic examination, and materials and heat treatment quality inspection, thought the ring appearance defect for burn holes, can be sure the ring is burnt. As to the number of ring bar defects when inspection into the factory did not find the original data, it can be sure the holes for the forging process. When bearing ring forging if heating temperature beyond the process temperature limit, in the temperature and heat preservation time is very long, the data will overheat, serious when burnt, not only the outer surface of the metal grain boundary by oxidation of crack, and areas with severe internal metal composition segregation, grain boundary also beginning of condensation, constitute Angle shaped cave. Stop forging in this state, data, came under heavy hammer forging parts have torn, constitute a large hole, large local show this kind of defect on the chamfer, end face and inner diameter. Forging burnt ring form of appearance such as orange peel, it spread has tiny cracks and thick skin. Because burn holes ring existed, burnt tissue damaged grain boundary, greatly divided the continuity of matrix, reduce the materials strength and plasticity, increase brittleness. Because of the appearance after ring forging is very thick, it is difficult to found burnt in the process, as long as the car just may appear after machining or grinding had burning characteristics. 3. Conclusion and initiative ( 1) The outer ring exists serious burnt hole is the direct reason of premature failure of the formed outer ring. （ 2) Burnt hole main components prior to the ring forging heating process, because of the heating furnace temperature 'run', the operator does not strict execution process procedures reason cause such as heating temperature is higher than the upper limit of temperature, operators should be after regular calibration furnace temperature curve, strict execution procedure, monitoring the process discipline's wrist and burnt probability. （ 3) Increase the inspection process, appropriate USES fluorescent magnetic powder stop inspection, the defects showed more clarity, pitting holes in forging defects caused by burning, found burnt ring, should be immediately discarded.