What Are The Reasons For The Cracking Of The Bearing Steel Ball?

The steel ball is the rolling body that carries the total load of the ball bearing and is also one of the important components of the bearing. However, in the process of using the bearing, we often find the cracking phenomenon of the bearing steel ball, such as: the bearing steel ball wear marks, the bearing steel ball has obvious extrusion, the bearing steel ball local defect, the bearing steel ball cracks and the surface of the steel ball.

1, according to the bearing steel ball cracking fracture analysis, some parts of the material are linear distribution, the edge is bright and uneven, there are obvious extrusion and wear marks of these bearing steel ball fracture phenomenon.

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

(1) The steel ball is cracked during use after being installed inside the bearing, and the cracking direction is the rolling direction of the material.

(2) There are obvious loose bands in the core of the steel ball, and the banded carbides exceed the standard and the surface contains abnormal elements such as oxygen, calcium and magnesium. In addition, the strip depth is about 0.25mm, which determines that there is a shrinkage hole residual in the heart of the steel ball, which is a metallurgical defect, which is also the main reason for the cracking of the steel ball during use.

(3) Overheating of the quenched tempered 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 reasons for cracking can be found by metallographic method by observing the relationship between the defect morphology and the metallographic structure.

2, The bearing steel ball is bright as a whole, and no high temperature discoloration is seen, but there is a crack of about 10mm, and there is a phenomenon of spalling near the crack.

After analysis, the reason for the cracking of the bearing steel ball is mainly due to the high quenching heating temperature, a large number of carbides are dissolved, so that the carbon content of austenite is significantly increased, and the network or semi-network carbides are formed in the grain boundary during cooling. By observing and analyzing the microstructure of the faulty steel ball, it is concluded that the fault steel ball appears overheating during the quenching process. At the same time, there are banded carbides in the steel ball structure, which makes the carbon-poor zone overripe during the heat treatment process. As a result, the large deformation of the steel ball during quenching is easy to lead to quenching cracks. That is to say, the quenching crack caused by the high quenching temperature.

The quenching crack refers to the crack produced during the quenching process or in the process of placing at room temperature after quenching, which is a macroscopic crack caused by the 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 working process.

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

3，Some bearing steel balls show local protrusions or ellipses, but the surface of the steel ball after husking is bright and complete.

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