The Secret to Bearing Steel Quality: Core Performance Indicators and Typical Defects
As a critical component in mechanical systems, the performance and life of rolling bearings depend largely on the quality of the bearing steel they are made of. To ensure stable operation under high loads and high speeds, extremely stringent technical requirements are imposed on the steel.
I. Core Performance Requirements for Bearing Steel
High Purity and Low Impurity Content
Non-metallic inclusions in steel (such as oxides and sulfides) are the source of fatigue cracks. Therefore, modern bearing steels generally utilize refining processes such as vacuum degassing and electroslag remelting to minimize sulfur, phosphorus, and gas content, thereby improving material uniformity and fatigue strength.
Precise Chemical Composition Control
Mainstream bearing steel is primarily high-carbon chromium steel (such as GCr15). Its carbon content must be stabilized between 0.95% and 1.05%, and its chromium content must be controlled between 1.30% and 1.65%. Precise proportioning ensures a high-hardness martensitic matrix and evenly distributed fine carbides after quenching, imparting the material with excellent wear and compressive resistance.
Microstructure Homogeneity and Low Defect Levels
The microstructure must be free of obvious banded segregation, Widmanstätten structure, or network carbides. The ideal quenched and tempered microstructure is cryptocrystalline martensite + finely dispersed carbides + an appropriate amount of retained austenite to ensure comprehensive mechanical properties.
Strict Surface and Dimensional Accuracy
The steel surface must be free of defects such as cracks, folds, and scars, and the depth of the decarburized layer must be within the specified range (typically ≤0.20mm). Furthermore, dimensional tolerances and shape accuracy directly impact subsequent processing efficiency and yield.
II. Common Metallurgical Defects and Their Impacts: Excessive Non-Metallic Inclusions
Large, brittle inclusions (such as Al₂O₃) can easily induce microcrack propagation in stress concentration areas, significantly reducing contact fatigue life.
Uneven carbide formation: Improper casting or heat processing can lead to the accumulation of carbides in bands or networks, weakening grain boundary strength and increasing the risk of brittle fracture.
Surface defects: Cracks and folds generated during the rolling process, if not promptly removed, can propagate during heat treatment, rendering the workpiece scrapped.
Excessively deep decarburization: A decrease in surface carbon content leads to insufficient quenching hardness and reduced wear resistance, impacting bearing accuracy and life.
In summary, the development and production of high-quality bearing steel is the result of the synergistic integration of metallurgical processes, materials science, and precision manufacturing. From controlling steel purity at the source to monitoring microstructural evolution throughout the entire process, every step is crucial to the reliability of the final product. In the future, as high-end equipment continues to demand higher performance from bearings, new materials such as ultra-clean steel and high-temperature bearing steel will continue to drive industry advancement.
Post time: Oct-30-2025
