A type bearing ring during early after pickling grinding found a white spot, raceway bearing materials for high temperature carburizing bearing steel G13Cr4Mo4Ni4V, the data is mainly used for air launch machine 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.
Bearing ring morphology and physical and chemical inspection coarse grinding race after pickling and guard should be the average film, defect ring white spot after pickling mainly distribute in the raceway and the gear side, as shown in figure 1.
Respectively in the bearing ring taking samples, white spot and normal in the sample section for metallographic organization at surface.
Metallographic specimen after mechanical grinding and polishing corrosion in 4% nitric acid alcohol solution, with GX - olin and company
51 metallographic microscope view of carburized layer microstructure and carbides distribute form, with certain organizations can be qualified and the carbide network can exceed bid.
Type ARL4460 direct reading spectrometry analysis is used to analyze the chemical composition of the sample, its composition can be qualified.
Using BUEHLER MICROMET type 5124 microhardness meter testing its hardness and depth of carburizing layer, certainly the carburized layer surface hardness and carburized layer depth.
Figure 1 ring morphology 2 after pickling.
The experimental results and analysis (
1)
Chemical composition analysis of chemical composition analysis results see table.
Analysis results indicate that chemical composition YB4106 - fit norms
2000 'air launched machine with high temperature carburizing bearing steel' request.
Chemical composition (G13Cr4Mo4Ni4V
The mass fraction)
（
%）
（
2)
Carburizing layer heat treatment group by high temperature after carburizing bearing steel carburizing heat treatment, carburizing layer microstructure appearance should be cryptocrystalline martensite, residual austenite and the average spread 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 examine microstructure and carbides in the race the two sample, color normal place of raceway surface microstructure of cryptocrystalline martensite, residual austenite and the average spread 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 residual 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 depth of carburizing layer the raceway BUEHLERMICROMET type 5124 microhardness meter testing and white spot area to the normal sample hardness and hardness gradient, certainly 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 match, raceway color normal surface hardness is 700 hv, about 60 HRC, the depth of carburizing layer 1.
28mm；
Raceway surface hardness is 639 hv, white spot place about 56.
5 HRC, carburized layer depth of 0.
96mm。
（
4)
Appearance carbon content type using ARL4460 direct reading spectrometry analysis instrument testing and white spot raceway sample appearance of normal carbon content, carbon content in normal race appearance is 0.
91%, the day the raceway surface carbon content is 0.
73%.
3.
The results and discussion on the basis of the above analysis, the bearing ring data qualified chemical composition;
Race color normal in appearance to 60 HRC hardness, carburized layer depth of 1.
28 mm, surface carbon content is 0.
91%;
Hardness of 56 raceway white spot in appearance.
5 HRC, carburized layer depth of 0.
96 mm, surface carbon content 0.
73%;
Raceway white spot in the surface microstructure of cryptocrystalline martensite and retained austenite, and found no residual carbide, carbon content and appearance below the normal place, can certainly bearing ring raceway area of the carbon content is low provoked showed a white spot after acid pickling.
Bearing ring white spot area of raceway appearance hardness is low, and the depth of carburizing layer, bearing contact fatigue life will be greatly reduced, the bearing spalling provoked the use of the process of early failure.
