Do you know how to pickle and passivate white spots on bearing rings? The production process for the bearing ring in Wafangdian is as follows: CNC lathe processing, carburization, low-temperature tempering, CNC lathe processing, secondary quenching, low-temperature tempering, precision grinding, acid washing and passivation.

1. Appearance and physicochemical inspection method of bearing ring

After precision grinding, acid washing, and passivation, the dovetail guide rail and retaining edge should be uniformly black. However, after acid washing and passivation, the white spots are mainly distributed at the dovetail guide rail and retaining edge, and samples are cut from the white spots on the bearing ring and normal areas. The cross-section of the sample is the observation surface of the alloy composition. The metallographic analysis sample was polished and polished by mechanical equipment, and then etched with a 4% hydrochloric acid ethanol solution. The metallographic structure and carbide distribution of the carburized layer were observed using an Olympus GX-51 stereomicroscope to confirm whether the mechanism meets the standard and whether the carbide network structure exceeds the standard. Analyze the composition of the sample using the ARL4460 direct reading spectral detector to confirm whether its composition meets the standard. Select the BUEHLER MICROMET 5124 Vickers hardness tester to test its strength and the depth of the carburized layer, and confirm the surface strength and depth of the carburized layer.

2. After comparing the carburizing heat treatment process of continuous high-temperature carburizing 45 # steel, the surface microstructure of the carburizing layer should be composed of cryptocrystalline austenite, residual austenite, and jointly distributed carbides, without network structure carbides or coarse carbides. Take the white spots and ordinary parts of the dovetail guide rail vertically and make metallographic analysis samples. Use the Olympus GX-51 stereomicroscope to observe the metallographic structure and carbides of the two samples of the dovetail guide rail. The metallographic structure on the surface of the dovetail guide rail at the normal color tone is cryptocrystalline austenite, residual austenite, and jointly distributed carbides. No network structure carbides or coarse carbides were found. According to the above research, the raw material composition of the bearing ring meets the standard; The surface strength of the dovetail guide rail with normal color tone is 60HRC, the deep layer of carburization is 1.28mm, and the surface carbon content is 0.91%; The surface strength at the white spot of the dovetail guide rail is 56.5HRC, the deep layer of carburization is 0.96mm, and the surface contains 0.73% carbon; The surface alloy composition at the white spot of the dovetail guide rail is composed of cryptocrystalline austenite and residual austenite. No residual carbides were found, and the surface carbon content is lower than normal. It can be known that the carbon content in some areas of the bearing ring dovetail guide rail is slightly low, resulting in white spots after acid washing and passivation.

The surface strength of the dovetail guide rail in the white spot area of the self-aligning roller bearing ring is relatively low, and the height of the carburized layer is shallow. The contact fatigue strength of the rolling bearing will be reduced, which is prone to detachment and early failure in the use of rolling bearings.