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Bearing steel new technology and direction
Bearing steel is primarily used in the manufacturing of rolling elements and races for rolling bearings. To ensure long life, high precision, low heat generation, high-speed operation, high rigidity, low noise, and excellent wear resistance, bearing steel must possess specific mechanical properties such as high hardness, uniform hardness, high elastic limit, high contact fatigue strength, adequate toughness, proper hardenability, and corrosion resistance in lubricants.
To meet these demanding requirements, the chemical composition of bearing steel must be highly uniform, with strict control over non-metallic inclusions, carbide particle size and distribution, and decarburization levels. Over time, bearing steels have evolved toward higher quality, better performance, and greater variety. They are typically categorized into high-carbon chromium bearing steel, carburized bearing steel, high-temperature bearing steel, stainless bearing steel, and special-purpose bearing materials, depending on their application environments and characteristics.
In response to the need for high-temperature, high-speed, high-load, corrosion-resistant, and radiation-resistant bearings, new types of bearing steels with unique properties have been developed. Advanced smelting techniques like vacuum melting, electroslag remelting, and electron beam remelting have been introduced to reduce oxygen content. Large-scale production now uses electric arc furnaces combined with primary refining and secondary metallurgy processes to achieve high-quality output.
Currently, bearing steel is produced using a process involving primary furnace, LF/VD or RH refining, continuous casting, and continuous rolling, with capacities exceeding 60 tons. This ensures high efficiency, low energy consumption, and superior quality. In heat treatment, traditional methods have evolved into continuous controlled atmosphere annealing furnaces, which can be over 150 meters long, ensuring stable and uniform spheroidized structures with minimal decarburization and lower energy use.
Since the 1970s, the expansion of industrial applications and international trade has driven the standardization of bearing steel and the adoption of new technologies and equipment. Countries like Japan and Germany have established high-purity, high-quality production lines, significantly improving steel quality and fatigue life. Japanese and Swedish bearing steels now have oxygen content below 10 ppm, with some reaching as low as 5.4 ppm.
The contact fatigue life of bearings is highly sensitive to the uniformity of the steel's microstructure. Improving cleanliness by reducing impurities and inclusions, promoting uniform distribution of non-metallic inclusions and carbides, and optimizing the microstructure—such as fine carbide particles in a tempered martensite matrix—can greatly enhance bearing performance. Key alloying elements include carbon, chromium, silicon, manganese, and vanadium.
Obtaining a spheroidized structure is critical in bearing steel production. Techniques like controlled rolling and cooling help eliminate network carbides, shorten spheroidizing annealing times, and improve fatigue life. Low-temperature controlled rolling (below 850°C) and short-time annealing have also been adopted, eliminating the need for spheroidizing annealing in some cases.
Research has shown that processing at around 650°C can enhance superplasticity in certain steels, allowing for energy savings and improved quality. The U.S. Naval Research Institute tested this method on 52100 steel, achieving impressive results without fracture at 650°C.
In heat treatment, advancements have focused on improving spheroidizing annealing, achieving finer, more uniform carbides, and even eliminating the process in some cases. Wire rod production now often uses two-step annealing, resulting in low-hardness, well-spheroidized structures with no reticulated carbides. This increases furnace efficiency by up to 30%.
New bearing steels are continuously being developed to replace traditional materials. Fast carburizing steels, for example, increase carburizing speed and reduce time from 7 hours to just 30 minutes. High-frequency quenching steels offer cost-effective alternatives to conventional bearing steels, improving service life and simplifying production.
Japanese steels like GCr465 and SCM465 show 2–4 times longer fatigue life than SUJ-2. New materials like M50NiL, 50X18M, and ceramic bearings are being developed for high-temperature, corrosive, and specialized applications.
China has developed high-hardenability steels like GCr15SiMo, offering improved contact fatigue life and durability. GCr4 steel, designed for impact resistance and energy efficiency, shows significant improvements in impact value and fatigue life compared to GCr15.
Looking ahead, bearing steel will continue to evolve in two main directions: increased cleanliness and diversified performance. Reducing oxygen content—from 28 ppm to 5 ppm—can extend bearing life by an order of magnitude. As operational environments become more demanding, new bearing steels tailored for high temperatures, corrosion resistance, and simplified processes will play a key role in future applications.