Failure analysis of 2018 - bearing steel ball
12 -
04 liang hua, Cheng Bin, kiki,
Luoyang Bearing Science & Technology Co. , ltd. steel ball is a ball Bearing in the Bearing load of rolling body, is one of the most important parts in the ball Bearing, the process is quite complicated, from cold heading (
Or hot rolling, forging)
Ball billet into a final cleaning packing, set and to many of the processing working procedure, and every processing procedure will create a larger inner and surface quality of the ball.
Steel ball manufacturing quality will directly affect the service life of the bearing, so it is extremely important.
Case of ball bearing failure caused by material metallurgy defects, analysis the difficulty is not big, but for small size ball craze, especially internal metallurgical defects caused by the cracking, due to the rolling direction is difficult to heat by pickling positioning materials, so the analysis of the difficulty will increase.
In this paper, using metallography, hardness test, analysis of macroscopic and microscopic observation, the method of thinking, analyzes the causes of cracking of steel ball.
A company inspection finished steel ball five (
Broke in half grain of the steel ball)
, it is GCr15 bearing steel material, machining process is as follows: & phi;
6.
0 mm hot rolled plates (
Continuous casting)
→
After spheroidizing annealing cold drawn into & phi;
4.
5毫米→
The stress relieving cold drawn into & phi;
3.
2毫米→
The stress relieving cold drawn into & phi;
2.
5毫米→
Cold heading ChengGangQiu & rarr;
Cold and hot working as & phi;
2.
36 mm finished product ball.
The batch ball 3 million grain, users in the use of about 60 granule found in the process of cracking in half, this paper analyzes the causes of cracking occurred on steel ball.
1.
Observation and analysis,
1)
Macro inspection of five and a half grain of fracture of steel ball are presented for linear distribution center part of the material, the edge light and uneven, has obvious extrusion, the wear trace, its morphology is shown in figure 1.
Figure 1 makes steel ball, macro (
2)
Microstructure observation and analysis of the fracture morphology in order to observe in more detail defects, take half grain of steel ball placed on a JMS -
6380 lv fracture morphology change times under scanning electron microscope observation, the results show that the steel ball center article about three 5 of the fracture appears as two-tone parallel banded, morphology nature, osteoporosis, the rest mainly appears as extrusion and wear conditions, local for porcelain fracture surface, microstructure of the fracture as shown in figure 2 to figure 5.
Using EDS7582 spectrometer on several parts of the strip in micro area composition analysis, abnormal found within the material elements, mainly for sodium, calcium, magnesium and trace amounts of oxygen.
Figure 2 ball fracture macroscopic fracture morphology figure 3 steel ball center location amplification figure 4 ball local microstructure morphology of local amplification figure 5 ball fracture morphology (
3)
Metallographic examination take a stripe of a single steel ball from the core horizontal anatomy, after grinding the observed: (1) strip profile depth is about 0.
Around 25 mm, stripe also exist a few small pore (
As shown in figure 6 and 7)
。
Figure 6 bands of steel ball the core section morphology figure 7 figure 6 partial enlarged morphology (2) the steel ball welt belt grinding, found that after using 4% nitric acid alcohol solution corrosion mainly located in the banded carbide in the same direction with the band (
See figure 8)
。
Figure 8 bands and banded carbide morphology of steel ball the core (3) steel ball banded carbide according to GB/T182542002 standard was rated grade 2.
Level 5 (
As shown in figure 9 and 10)
And do not conform to the requirements of the standard.
Figure 9 figure 8 partial enlarged morphology figure 10 local microstructure morphology in figure 9 (4) steel quenching tempering organization overheating and uneven, according to standard JB/T12552014 assessment for more than 4, carbide network for level 2, do not conform to the requirements of the standard (
See figure 11)
。
Figure 11 steel quenching tempering group 2.
Results according to the macro and micro observation can be determined: (the results of analysis and metallographic examination
1)
After installation into the bearing steel ball is used in the process of cracking, cracking direction to the direction of rolling material.
（
2)
Steel ball core has obvious loose stripe, banded carbide overweight and the surface contains oxygen, anomaly element such as calcium, magnesium, in addition, the stripe have depth, about 0.
25 mm, which determine the existence of steel ball the core porosity, belongs to the metallurgical defects, which is lead to steel ball in the use of the main causes of crack occurring in the process.
（
3)
Steel ball that overheating quenching tempering brittleness increases, reduced the compressive strength, make the ball more prone to cracking.
3.
Epilogue makes steel ball craze is cracking in the process of bearing operation, material defects and heat treatment defect is both the result of joint action, belongs to the cracking defects;
Existence of steel ball the core residual and banded carbide excessive shrinkage cavity is given priority to, quenching and tempering heat treatment organization overheating make steel ball brittleness increases is also one of the reasons result in the crack of the steel ball.
When the small size of steel ball or fracture extrusion, and serious wear and tear, unable to determine material rolling direction, also hard to do regular fracture analysis, can by the metallographic method, by observing the relationship between morphology and microstructure defects found the main cause of cracking.
