The “inner strength” secret of bearing steel: exploring the material foundation of high-end rolling bearings
From: XingMao DATE: 2025/8/15 Hits: 941
The “inner strength” secret of bearing steel: exploring the material foundation of high-end rolling bearings
From high-speed railways to deep-sea drilling equipment, from precision CNC machine tools to wind turbines, rolling bearings serve as the ‘joints’ of modern industrial equipment. Their operational stability and service life directly determine the reliability and efficiency of the entire machine. Behind all this lies bearing steel—a seemingly ordinary metal m...
From high-speed railways to deep-sea drilling equipment, from precision CNC machine tools to wind turbines, rolling bearings serve as the ‘joints’ of modern industrial equipment. Their operational stability and service life directly determine the reliability and efficiency of the entire machine. Behind all this lies bearing steel—a seemingly ordinary metal material that is, in fact, the ‘hidden champion’ determining the upper limit of bearing performance. Among these, the precision of the smelting process and the purity of the material constitute the true ‘gold standard’ for bearing steel.
The ‘hard criteria’ for high-end bearing steel
Bearings operate under high-speed, heavy-load, and long-cycle conditions, imposing nearly苛刻 demands on material performance. Therefore, the smelting of bearing steel is not merely a matter of alloy composition but a challenge to the limits of metallurgy.
Firstly, precise control of chemical composition is fundamental. For high-carbon chromium bearing steels like GCr15, carbon and chromium content must be strictly controlled within an extremely narrow range. Excessively high carbon content can lead to increased brittleness, while too low a content affects hardness; chromium content directly impacts quenching hardenability and wear resistance, with deviations exceeding 0.05% potentially causing performance fluctuations.
Secondly, steel purity is considered a core indicator. Non-metallic inclusions, especially oxides and sulphides, are the primary causes of bearing fatigue failure. International advanced standards require total oxygen content (T.O.) in steel to be below 10 ppm per kilogram, with inclusion sizes controlled to less than 10 micrometres. This is equivalent to ‘capturing’ invisible impurities in a tonne of molten steel.
Furthermore, the uniformity of the microstructure is equally critical. Ideal bearing steel should have fine, uniformly distributed carbide particles, avoiding banded segregation or network carbides. This not only enhances material strength but also ensures consistent performance after heat treatment.
The ‘battle’ of the smelting process
Achieving the above standards presents numerous technical challenges. For example, trace elements such as calcium, aluminium, and titanium, though present in extremely low concentrations, can easily form high-melting-point inclusions that affect the fatigue life of the steel. Additionally, preventing secondary oxidation and maintaining the cleanliness of the molten steel during continuous casting remains a long-standing industry challenge.
To overcome these challenges, leading domestic companies have widely adopted a full-process production chain comprising ‘electric furnace primary smelting + LF refining + RH vacuum degassing + continuous casting with protective pouring.’ Through vacuum degassing technology, hydrogen content can be reduced to below 1.5 ppm, significantly lowering the risk of white spots. Meanwhile, the application of electromagnetic stirring and light pressure reduction technology effectively improves centre segregation in ingots and enhances microstructural uniformity.
Some high-end production lines have also introduced inclusion modification technology, using calcium treatment to convert brittle aluminium oxide into spherical calcium aluminate, thereby reducing its harmful effects. Additionally, large-pressure forging processes are employed to further compact the internal structure and eliminate potential defects.
Application Example: Material Differences, Lifespan Differences
A manufacturer of wind turbine main shaft bearings compared the use of bearing steel with different purity grades: Batch A had a total oxygen (TO) content of 8 ppm, while Batch B had 15 ppm. After operating under the same conditions for 20,000 hours, the fatigue life of Batch A bearings exceeded the design value by 30%, while Batch B already exhibited early pitting corrosion. This case clearly demonstrates that even minor material differences can result in several-fold differences in service life.
In the high-speed railway bearing sector, one of the key reasons for the long-term dominance of foreign brands is their mastery of core technologies for ultra-pure steel production and microstructure control. In recent years, domestic companies have achieved partial substitution in high-end products through technology introduction and independent innovation, but overall material stability still has room for improvement.
Conclusion: Laying a solid foundation is essential for steady progress
The quality of bearing steel production is a critical ‘foundational logic’ in the domestic production of high-end bearings. It not only affects the performance of individual products but also impacts the reliability of the entire equipment manufacturing industry. In the future, only by continuously increasing investment in metallurgical basic research, process equipment upgrades, and quality control systems, and promoting deep integration between industry, academia, and research, can we truly break through the ‘chokepoint’ constraints.
The industry is calling for the establishment of a unified high-standard material certification system, strengthening upstream-downstream collaboration, and enhancing the overall quality of China's bearing steel from the source. Only in this way can China's bearing industry transition from ‘following’ to ‘keeping pace’ and even ‘leading’ in global competition.
