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Factors Affecting Bearing Steel Quality


The main material of the bearing is bearing steel, and its quality has extremely strict requirements on the internal structure of the bearing, the uniformity of chemical composition, the content of non-metallic inclusions, the size and distribution of carbide particles, and the degree of decarburization. Therefore, when selecting bearing steel, we must conduct strict screening.

Regarding the factors that affect the quality of bearing steel, we can conduct an in-depth analysis from both internal and external perspectives. Starting from the bearing steel itself, we can explore its internal composition and characteristics; at the same time, we cannot ignore the possible impact of external factors on its quality.

External factors:

  • Dimensional accuracy: The dimensional accuracy of bearing steel directly affects the processing and assembly quality of parts. If the dimensional accuracy is inaccurate, it may cause the bearing parts to not be assembled correctly, or even damage the equipment and molds.
  • Surface defects: Defects on the surface of bearing steel, such as cracks, slag inclusions, burrs, etc., will affect the processing quality and performance of the bearing, and even shorten the bearing life.

Internal factors:

  • Inclusions: Inclusions in bearing steel can cause stress concentration and easily cause cracks and other defects, thus affecting the fatigue life of the bearing.
  • Carbide: The content, shape and distribution of carbide will affect the hardness and wear resistance of bearing steel, directly affecting the service life of the bearing.
  • Gas content: The content of oxygen, nitrogen, hydrogen and other gases will affect the purity of bearing steel. High content of gas may lead to the formation of inclusions, thereby affecting the quality of bearing steel.
  • Center porosity and center segregation: These internal defects will cause unevenness of the bearing steel and affect its mechanical properties and service life.
  • Consistency of product performance: During the production process of bearing steel, the performance of each batch of products is required to be consistent to ensure the replaceability and stability of the bearings between different batches.


These factors can be summarized into three main indicators: dimensional accuracy and surface quality, purity and uniformity. Let me briefly explain these three indicators:

Dimensional accuracy and surface quality

The dimensional accuracy of bearing steel is critical to ensuring the precise processing and assembly of bearing parts. Inaccurate dimensions will not only affect the accurate calculation of blank size and weight, but may also cause damage to equipment and molds. At the same time, surface quality also has a direct impact on the processing accuracy, performance and life of the bearing. Obvious surface defects such as cracks, slag inclusions, burrs, scars, oxide scale, etc. may affect the reliability and service life of the bearing.


The purity of bearing steel is one of the important indicators to measyre its quality. High purity steel means low levels of non-metallic inclusions, which helps reduce stress concentrations during forging and the formation of heat treatment defects. The level of purity directly affects the fatigue life of the bearing, because the presence of inclusions will significantly reduce the contact fatigue life of the bearing steel. Research shows that there is a negative correlation between the content of inclusions in steel and the contact fatigue life of bearing steel.

Tissue uniformity

The structural uniformity of bearing steel is crucial to ensure the heat treatment deformation and structural uniformity of the bearing during the manufacturing process. The fine and dispersed distribution of inclusions and carbide particles contributes to improved bearing performance and service life. On the contrary, if the particle size of inclusions and carbides is large and unevenly distributed, the service life of the bearing will be shortened. Therefore, ensuring the structural uniformity of bearing steel is one of the key factors to ensure bearing quality.