Bearing ring pickling white spot analysis - bearing knowledge

A type bearing ring during early after pickling grinding found white spot appears, raceway bearing materials for high temperature carburizing bearing steel G13Cr4Mo4Ni4V, the material is mainly used for aviation engine bearing, the working temperature is 315 ℃. The processing technology of the bearing ring for: car manufacture to carburizing, high temperature tempering to return the car processing, secondary quenching and high temperature tempering to coarse grinding, pickling. 1. Coarse grinding bearing ring morphology and physical and chemical inspection method after pickling raceway and the guard should be evenly colored, defect ring after pickling plaques are mainly distributed in the race and gear side, as shown in figure 1. Respectively in the bearing ring taking samples, white spot and normal in the sample section of surface microstructure observation. Metallographic specimen after mechanical grinding and polishing corrosion in 4% nitric acid alcohol solution, with GX - olin and company 51 metallographic microscope observation of carburized layer microstructure and distribution of carbide shape, to determine whether the organization is qualified and carbide network exceeds bid. Application type ARL4460 direct reading spectrometer analysis of the chemical composition of the sample, to determine whether its composition is qualified. Using BUEHLER MICROMET type 5124 microhardness meter testing its hardness and depth of carburizing layer, determine its surface hardness and carburized layer depth of carburizing layer. Figure 1 ring morphology 2 after pickling. The test results and analysis ( 1) Chemical composition analysis of chemical composition analysis results see table. The analysis results show that the chemical composition in accordance with standard YB4106 - 2000 the aircraft engine with high temperature carburizing bearing steel requirements. Chemical composition (G13Cr4Mo4Ni4V The mass fraction) ( %) ( 2) Carburizing layer tissue contrast high temperature carburizing bearing steel carburizing heat treatment after heat treatment, surface carburizing layer should be cryptocrystalline martensite, residual austenite and uniform distribution of carbide, can not have network carbide and massive carbide. Vertical profile control of raceway vitiligo and normal part respectively made metallographic specimen, the olin ba si GX - 51 metallographic microscope to observe microstructure and carbides in the race the two sample, color normal place of raceway surface microstructure of cryptocrystalline martensite, residual austenite and uniform distribution of carbide, carbide network and are not found in bulky carbide, as shown in figure 2 a; White spot in the raceway surface microstructure of cryptocrystalline martensite and retained austenite, carbide network and are not found in bulky carbide, as shown in figure 2 b. ( 一) Color normal place of raceway cross section microstructure ( b） White spot in the raceway cross section microstructure figure 2 raceway surface microstructure pictures with 4% nitric acid alcohol solution to wipe the white spot cross section sample, secondary hardening burns has not been found. ( 3) Surface hardness and carburized layer depth of the raceway BUEHLERMICROMET type 5124 microhardness meter testing and white spot area to the normal sample hardness and hardness gradient, determine the two sample surface hardness and carburized layer depth. In normal race color sample hardness gradient curve as shown in figure 3 a, raceway of white spot sample hardness gradient curve is shown in figure 3 b. By figure 3 a, 3 b is available, raceway color normal surface hardness is 700 hv, about 60 HRC, the depth of carburizing layer 1. 28mm； Raceway leukoplakia in surface hardness is 639 hv, about 56. 5 HRC, carburized layer depth of 0. 96mm。 ( 4) Surface carbon content using ARL4460 direct reading spectrometer test and normal white spot raceway carbon content on the surface of the specimen, the normal place of raceway surface carbon content is 0. 91%, the day of raceway surface carbon content is 0. 73%. 3. Results and discussion based on the above analysis, the bearing ring material chemical composition of qualified; Raceway surface hardness of 60 HRC color normal place, the depth of carburizing layer 1. 28 mm, surface carbon content is 0. 91%; Surface hardness is 56 race white spot. 5 HRC, carburized layer depth of 0. 96 mm, the surface carbon content 0. 73%; Raceway white spot in the surface microstructure of cryptocrystalline martensite and retained austenite, and found no residual carbides, and the surface carbon content lower than normal, can determine the bearing ring raceway local regional low carbon content cause white spot after pickling. Bearing ring raceway surface hardness is low, white spot area and the depth of carburizing layer, the contact fatigue life of bearing will be greatly reduced, peeling off in the use of the bearing process cause early failure.