Oversize bearing outer ring early failure reason analysis - bearing knowledge

A double LieDiao roller bearing users reflect a set of oversize bearings bearings bearings in use process found their to appear early failure, the set of bearing ring is used for cement grinding roller, poor working conditions. The model material as GCr15SiMn steel, its processing process is: phi 300 mm raw materials into the factory ultrasonic testing - blanking piece - metal forging - spheroidizing annealing - car processing and heat treatment to detection to grinding, inspection, assembly into the Treasury. Now the author carries on the physical and chemical inspection analysis, the failure reasons. 1. The physical and chemical inspection ( 1) Macroscopic examination outer ring by gas cutting sampling, whole raceway surface friction and wear phenomenon, local area is 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 analysis of foreign circle sampling, the size is 15 mm * 15 mm * 15 mm, using direct reading spectrometer to chemical composition analysis, test results are shown in table 1, the chemical composition in accordance with GB/T18254 - 2016 GCr15SiMn standard requirements. The main chemical composition (table 1 outer ring The mass fraction) ( %) ( 3) Metallographic examination first, macroscopic observation. Making the hole part fracture observation, sample after mouth visible fracture surface roughness, shiny grain surface edges, in addition to this, also distributed holes, commonly known as 'tofu' fracture, the fracture morphology as shown in figure 2 a shows. Test of arbitrary cross section after the macroscopic observation, visible surface has a large hole distribution, edge Angle shaped, individual holes bottomless, its exterior appearance is shown in figure 2 b. ( 一) Fracture ( b） Metallographic, macro figure 2 second, metallographic observation. For making the hole site section after the metallographic specimen OLYMPUSGX51 microscope, visible on the cross section has a large number of irregular Angle hole distribution, 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 observed under scanning electron microscopy (sem), visible fracture distribution have a large number of Angle hole, hole metal melt morphology is local, as shown in figure 4. Figure 4 holes microscopic morphology ( 4) Material and heat treatment after making outer ring vertical and horizontal section metallographic specimen quality detection, and observed under optical microscope according to the material standard of GB/T 18254 - And heat treatment standard JB/T 1255-2016 2014 assess, test results as shown in table 2 and table 3 respectively, the above test results are accord with a standard to ask. Table 2 outer material quality inspection table 3 outer heat treatment quality grade project supporting organization/austenite martensite structure levels/carbide mesh/hardness HRC outer ring 2, 3, 1. 0 to 60, 61, 61, standard 2 1 ~ 4 or less 2 or less. 5 58-63 2. Analysis based on the ring macroscopic examination, composition analysis, metallographic examination, and materials and heat treatment quality inspection, think that the ring surface defect for burn holes, the ring can be determined is burnt. As, the number of ring bar into the factory inspection found no raw material defect, which can determine the hole is formed in the process of forging. When bearing ring forging if heating temperature exceeding the maximum limit of process temperature, the temperature and heat preservation time is long, the material will overheat, serious when burnt, not only the surface layer of metal grain boundary by oxidation of crack, and areas with severe internal metal composition segregation, grain boundary are also beginning to melt, forming Angle shaped cave. In this state for forging, the material by a heavy hammer forging, torn parts, form a larger holes, most of such defects appear on the chamfer, end face and inner diameter. Forging burnt ring surface morphology, such as orange peel, the distribution of small cracks and thick oxide skin. Because burn holes ring existed, burnt tissue destroyed the grain boundary, greatly divided the continuity of matrix, reduce the material's strength and plasticity, increase brittleness. Because after ring forging surface has a very thick oxide skin, it is difficult to found burnt in the process, only after the car or grinding machining might been burning characteristics. 3. Conclusions and recommendations, 1) The outer ring exists serious burn holes is the direct cause of premature failure of the outer ring. ( 2) Burnt hole mainly formed in the ring heating process before forging, due to the heating furnace temperature 'run', the operator does not strictly enforce process discipline ceiling causes such as heating temperature is higher than the processing temperature, should be through regular calibration furnace temperature curve, operations staff strictly enforce process discipline, monitoring the process discipline and other means to reduce the probability of burnt. ( 3) Increase the inspection process, appropriate USES fluorescent magnetic particle inspection, make the defects showed more clear, pitting holes in forging defects caused by burning, found burnt ring, should be scrapped immediately.