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What are the factors affecting the fatigue life of bearing steel

2022-05-07

There will be such and other problems when the slewing bearing is used, so it has a certain service life from its production, which is also the theoretical service life. In fact, the service life of the bearing is not only affected by the use environment and external factors. It is related to its own production materials, such as the hardness of rotary bearing steel, etc. The following editors from Zhiyuan will introduce to you the factors that affect the fatigue life of bearing steel.

 

slewing bearing

 

Factors affecting the fatigue life of bearing steel

 

1. The effect of nitrides on fatigue life

 

Some scholars have pointed out that when nitrogen is added to the steel, the volume fraction of nitrides decreases. This is due to the reduction in the average size of the inclusions in the steel. Limited by technology, there are still a considerable number of inclusion particles smaller than 0.2 in. counted. It is precisely the existence of these tiny nitride particles that has a direct impact on the fatigue life of bearing steel. Ti is one of the elements that form nitrides. It has a small specific gravity and is easy to float. There will also be a part of Ti left in the steel to form multi-angular inclusions. Such inclusions are likely to cause local stress concentration and fatigue cracks, so it is necessary to control the occurrence of such inclusions.

 

2. The influence of oxides on fatigue life

 

The oxygen content in steel is an important factor affecting the material. The lower the oxygen content, the higher the purity and the longer the corresponding rated life. The oxygen content in steel is closely related to oxides. During the solidification process of molten steel, the dissolved oxygen of aluminum, calcium, silicon and other elements forms oxides. The oxide inclusion content is a function of oxygen. As the oxygen content decreases, the oxide inclusions will decrease; the nitrogen content is the same as the oxygen content, and also has a functional relationship with the nitride, but because the oxide is more dispersed in the steel, it plays the same role as the carbide. , so it has no destructive effect on the fatigue life of steel.

 

Due to the existence of oxides, steel destroys the continuity of the metal matrix, and because the expansion coefficient of oxides is smaller than the expansion coefficient of the bearing steel matrix, when subjected to alternating stress, it is easy to generate stress concentration and become the origin of metal fatigue. Most of the stress concentration occurs between oxides, point inclusions and the matrix. When the stress reaches a sufficient level, cracks will occur, which will rapidly expand and destroy. The lower the plasticity of the inclusions and the sharper the shape, the greater the stress concentration.

 

slewing bearing

 

3. The effect of sulfide on fatigue life

 

Almost all of the sulfur content in steel exists in the form of sulfides. When the sulfur content in the steel increases, the sulfide in the steel increases accordingly, but because the sulfide can be well surrounded by the oxide, the influence of the oxide on the fatigue life is reduced, so the number of inclusions has no effect on the fatigue life. Certainly, it is related to the nature, size and distribution of inclusions. The more inclusions, the lower the fatigue life must be, and other influencing factors must be considered comprehensively. In bearing steel, sulfides are dispersed and distributed in a fine shape, and are mixed with oxide inclusions, which are difficult to identify even by metallographic methods. Experiments have confirmed that on the basis of the original process, increasing the amount of Al has a positive effect on reducing oxides and sulfides. This is because Ca has a fairly strong desulfurization ability. Inclusions have little effect on the strength, but are more harmful to the toughness of the steel, and the degree of damage depends on the strength of the steel.

 

The above is a summary of the factors that affect the fatigue life of bearing steel. In fact, if we want to improve the service life of bearing steel, we can start from the heat treatment process and machining accuracy of bearing materials and the later use specifications of bearings. Our Yantai Zhiyuan factory has rich experience in the production of Slewing Ring Bearing, with excellent production technology and good product quality. It is exported to dozens of countries and regions. If you need it, please send us a message for details.