What Are the Reasons For Bearing Steel Ball Cracking

Time：2021.04.01  Source：Roller Bearings Suppliers

What is bearing steel ball cracking

Steel ball is a total bearing load of ball bearing, the roller is one of the important components of bearing, but we are in the process of using bearings, often find bearing steel ball cracking phenomena, such as: bearing steel ball wear trace, bearing steel ball has obvious extrusion, partial defects of bearing steel ball, steel ball bearings in cracks and steel ball surface spalling, etc.

According to the analysis of bearing steel ball cracking fracture, some parts of the material are linear distribution, bright and uneven edges, and there are obvious extrusion and wear traces of these bearing steel ball fracture phenomena. Need WSBC 22216 E, click here to learn more.

Causes of bearing steel ball cracking

After analysis, there may be three possible causes of bearing steel ball cracking:

(1) The steel ball cracks in the process of use after it is installed inside the bearing, and the cracking direction is the rolling direction of the material.

(2) There is an obvious loose strip in the core of the steel ball. The banded carbide exceeds the standard and the surface contains abnormal elements such as oxygen, calcium and magnesium. In addition, the strip depth is about 0.25mm, so it is determined that there is a residual shrinkage hole in the core of the steel ball, which is a metallurgical defect, which is also the main reason for the cracking of the steel ball in the process of use.

(3) overheating of the quenching and tempering structure of the steel ball increases its brittleness, reduces the compressive strength, and makes the steel ball more prone to cracking.

When the size of the steel ball is small or the fracture extrusion and wear are serious, the rolling direction of the material cannot be determined, and it is difficult to carry out conventional fracture analysis. At this time, the main reason for cracking can be found by the metallographic method and by observing the relationship between the defect morphology and metallographic structure.

The condition of bearing steel ball at high temperature

The bearing steel ball is bright on the whole without discoloration at high temperature, but there is a crack of about 10mm in length, and there is a phenomenon of peeling near the crack.

The analysis shows that the main reason for cracking of the bearing steel ball is that the quenching temperature is too high and the carbide is dissolved in large quantities, which makes the carbon content of austenite increase obviously, and the mesh or semi-mesh carbide is formed at the grain boundary during cooling. By observing and analyzing the metallographic structure of the fault steel ball, it is concluded that the fault steel ball appears to overheat during quenching. At the same time, the presence of banded carbides in the steel ball structure makes the carbon-poor zone overripe during heat treatment. So that the steel ball in the quenching deformation is easy to lead to the quenching crack. That is to say, quenching cracks caused by excessive quenching temperature.

Quenching crack refers to the crack produced in the quenching processor in the room temperature placement process after quenching. It belongs to a macroscopic crack and is caused by macroscopic internal stress. After quenching cracking occurs, contact fatigue spalling occurs under the influence of quenching crack defects and periodic pulsating contact stress in the subsequent work. Click here to learn more about WSBC 22217 E.

Note: During the steel ball heat treatment process, the heat treatment process parameters should be strictly controlled to ensure the stability of heat treatment temperature and holding time.

Influence of bearing steel ball microstructure

Some bearing steel balls show a local bulge or oval shape, but the surface of the steel ball after peeling is bright and complete.

When the size of the steel ball is small or the fracture extrusion and wear are serious, the rolling direction of the material cannot be determined, and it is difficult to carry out conventional fracture analysis. At this time, the main reason for cracking can be found by the metallographic method and by observing the relationship between the defect morphology and metallographic structure.

The reason for this phenomenon of bearing steel ball may be caused by external factors such as operating conditions, but a considerable part is caused by the factors of the steel ball itself. For example, raw material defects or manufacturing defects, and raw material factors are mainly divided into three aspects: surface defects, low-power tissue defects and microscopic structure defects. Another part of the bearing steel ball failure may also be caused by fatigue.

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