Data elements affecting bearing life and its manipulation
August 06 06:20:07, 2025
**Data Elements Affecting Bearing Life and Their Control**
Home > Bearing Knowledge > Data Elements and Their Control That Affect Bearing Life
Source: China Bearing Network | Time: 2013-06-06
Bearing life is influenced by a variety of factors, including material properties, microstructure, and heat treatment processes. The early failure modes of rolling bearings typically involve cracking, plastic deformation, wear, corrosion, and fatigue. Under normal conditions, the primary cause of failure is fatigue. However, other factors such as hardness, strength, durability, wear resistance, and internal stress also play critical roles in determining bearing performance.
One of the key elements affecting bearing life is the carbon content in quenched martensite. For high-carbon chromium steel (such as GCr15), the original microstructure before quenching—often granular pearlite—has a significant impact on the mechanical properties of the final product. When the carbon content in martensite is around 0.5%, the mechanical performance reaches its peak, with optimal fatigue life and resistance to crushing.
The martensite obtained after quenching is usually fine-grained and cryptocrystalline. This structure helps prevent microcracks that can occur during the quenching of high-carbon steels. The substructure consists of dislocation-type lath martensite, which provides high strength and resistance. Therefore, achieving the correct amount of martensite with uniform carbon distribution is essential for maximizing bearing performance.
Another important factor is the amount of retained austenite (Ar) in the hardened steel. After normal quenching, GCr15 steel may contain 8% to 20% Ar. While Ar can improve toughness, it can also reduce hardness if present in excess. Studies show that increasing the Ar content initially improves hardness and fatigue life, but beyond a certain point, the benefits decrease. The optimal Ar content for hardness is around 17%, while the peak fatigue life occurs at about 9%.
Undissolved carbides also have a significant effect on bearing life. These carbides are hard and brittle, and their presence can lead to stress concentration and cracking. Proper control of carbide size, distribution, and quantity is necessary to ensure good mechanical properties. Excess undissolved carbides can reduce hardness, strength, and fatigue life. To minimize these effects, it's important to achieve a fine and uniform microstructure through proper heat treatment.
Residual stresses after quenching and tempering also influence bearing performance. Compressive residual stresses can enhance fatigue life, while tensile stresses can reduce it. Controlling the cooling process and using surface treatments like carburizing or nitriding can help introduce beneficial compressive stresses. For example, carburized parts show significantly improved touch fatigue life compared to non-carburized ones.
Impurity content in the steel, such as oxygen, nitrogen, phosphorus, and oxides, also affects bearing performance. High levels of impurities can reduce ductility, strength, and fatigue life. Using advanced refining techniques like electroslag remelting or vacuum arc remelting can help achieve high-purity steel suitable for bearing applications.
To optimize bearing life, several key factors must be controlled:
1. Fine and uniformly dispersed carbides in the original microstructure.
2. Proper quenching temperature and time to achieve an ideal martensitic structure with about 0.55% carbon, 9% retained austenite, and 7% undissolved carbides.
3. Surface compressive stress after tempering, which can be enhanced through carburizing or nitriding.
4. High-purity steel with low oxygen and nitrogen content.
By carefully managing these elements, bearing manufacturers can significantly extend the service life and reliability of their products.