New technologies and the development direction of bearing steel
Rolling bearing steel is mainly used in the manufacture of rolling elements and rings.
Since the bearing should have a long life, high-precision, low heat, high speed, high rigidity, low noise, high wear resistance and other characteristics, thus requiring bearing steel should have: high hardness, uniform hardness, high elastic limit, high contact fatigue strength and toughness necessary, certain hardenability in the air bearing the company's lubricant corrosion resistance. To achieve the above performance requirements, bearing steel chemical composition uniformity, non-metallic inclusion content and type, size and distribution of carbides, decarburization demanding.
Bearing steel to the development of high quality, high performance and multi-species direction as a whole. Bearing steel according to characteristics and application environments are divided into: carbon chromium bearing steel, carburizing bearing steel, high temperature bearing steel, stainless steel and special bearing special bearing materials.
To meet the high-temperature, high-speed, high load, corrosion, anti-radiation engineering machinery bearing requirements, the need to develop a series of new bearing steel with special properties. In order to reduce the oxygen content of bearing steel, the development of vacuum smelting, remelting, electron beam remelting bearing steel smelting technology. The large quantities of imported bearings bearing steel smelting by arc melting, develop into various types of foreign First Canadian refining furnace.
Currently, the use of early capacity greater than 60 tons furnace + LF / VD or RH + + continuous casting and rolling bearing steel production process, in order to achieve high-quality, high efficiency, low energy consumption purposes. In terms of the heat treatment process by car bottom furnace, bell furnace developed into a continuous annealing furnace controlled atmosphere heat treatment. Currently, continuous heat treatment furnace up to 150m, processing bearing steel ball of the organization stable and uniform, decarburization is small, low energy consumption.
Since the 1970s, along with economic development and industrial technological progress, expand the scope of application of the bearing; and the development of international trade, but also to promote the development and application of international standards of bearing steel and new technologies, new processes and new equipment, efficiency , high quality, low cost of supporting technology and process equipment came into being. Japan and Germany etc. built a high purity, high-quality bearing steel production line, steel production increased rapidly and dramatically improve the quality of the fatigue life of the steel. Japan and Sweden, the oxygen content of bearing steel production down to 10ppm or less. The late 1980s, Japan's Sanyo Special Steel Company's advanced level of 5.4ppm, reached the level of vacuum remelting bearing steel.
Contact fatigue life of the bearing on the uniformity of the steel structure is very sensitive. Improve the cleanliness (reduction of impurity elements in steel and inclusion content), to promote non-metallic inclusions in steel and carbide fine and uniform distribution, can increase the contact fatigue life of bearing steel. Tissue bearing steel using state should be evenly distributed fine carbide particles tempered martensitic matrix, such organizations can give the required performance of the bearing steel. Carbon bearing steel in the main alloying elements carbon, chromium, silicon, manganese and vanadium.
How to get the ball bearing steel production organization is an important issue, controlled rolling and cooling is important advanced bearing steel production process. Through the controlled rolling or cold rolling fast eliminate network carbide to obtain suitable tissue preparation, ball bearings can be shortened annealing time, refining carbide, improve fatigue life.
In recent years, Russia and Japan controlled rolling and low temperature (800 ℃ ~ 850 ℃ or less), plus air cooling after rolling a short anneal, or completely cancel spheroidizing, you can get qualified bearing steel structure. Bearing steel 650 ℃ temperature processing is also new technology. Before eutectoid steel or high carbon steel having a thermal processing if the fine grain, or during processing to form fine grains, then (0.4 to 0.6) the melting temperature in the range, at a certain strain rate, exhibit superplasticity. Naval Postgraduate School (NSP) for 52100 steel processing temperature of 650 ℃ tests showed that at 650 ℃ 2.5 true strain fracture does not occur. Therefore, it is possible to 650 ℃ temperature and high-temperature processing instead of processing combined with the ball annealing process, which simplifies the equipment and processes, save energy, improve quality is important.
In terms of heat treatment, to improve the quality of ball annealing, to obtain small, uniform, spherical carbides and shortening the annealing time or cancel ball annealing step of research progress has been made, namely wire rod produced using organized two annealing, the drawing after 720 ℃ ~ 730 ℃ to 760 ℃ annealing recrystallization annealing organization. So you can get a low hardness, ball, and no carbide network organization, the key to ensure that the intermediate drawing reduction rate ≥14%. The process of the heat treatment furnace efficiency increased by 25% to 30%. Continuous ball annealing heat treatment technology is the development direction of bearing steel heat treatment.
All countries in the research and development of new bearing steel, and expand the application instead of the traditional steel bearing. The quick carburizing bearing steel, by changing the chemical composition to increase the rate of carburization, wherein the carbon content increased from the conventional 0.08% to 0.20% to about 0.45%, to shorten the carburizing time from 7 hours to 30 minutes. The development of high-frequency hardening bearing steel, carbon steel or ordinary carbon manganese, chromium steel, hardened by high-frequency heating to replace the ordinary bearing steel, not only simplifies the manufacturing process and reduce the costs and increase the service life.
Japan developed GCr465, SCM465 fatigue life than SUJ-2 2 ~ 4 times higher. Due to the use of bearing more and more, M50 (CrMo4V) used in the past, 440C (9Cr18Mo) bearing steel, etc. can not meet the requirements, the urgent need to develop processing performance, low cost, high temperature fatigue in harsh, corrosive, lubrication conditions environment long life, can be suitable for different purposes and uses steel bearings, such as high temperature carburizing steel M50NiL, easy processing stainless steel bearings and ceramic bearings 50X18M materials. For GCr15SiMn steel quenching low weaknesses, China's development of high hardenability and hardenability bearing steel GCr15SiMo, its hardenability HRC≥60, hardenability J60≥25mm. GCr15SiMo contact fatigue life L10 and L50, respectively, compared GCr15SiMn by 73% and 68%, under the same conditions, the service life of the bearings with G015SiMo steel is twice GCr15SiMo steel. In recent years, China has developed the energy savings, resource conservation and impact GCr4 bearing steel. Compared with GCr15, GCr4 impact value increased by 66% and 104%, fracture toughness increased by 67%, contact fatigue life L10 increased by 12%. GCr4 steel bearing high temperature heating - surface hardening heat treatment process. And full hardenability of GCr15 bearing steel compared, GCr4 steel bearing life significantly improved, high-speed train can be used for heavy-duty bearings. Bearing steel next major development in two directions diversified high cleanliness and performance. Improve the cleanliness of the bearing steel, in particular reducing the oxygen content in steel, can significantly extend bearing life. Oxygen levels ranging from 28ppm down to 5ppm, the fatigue life can be extended an order of magnitude. To prolong the life of the bearing steel, it has been committed to the development and application of refined techniques to reduce the oxygen content in the steel.
Through unremitting efforts, bearing steel, the minimum oxygen content from the 1960s to the 1990s to reduce 28ppm 5ppm. At present, China may be bearing steel, the minimum oxygen content control at about 10ppm. Changes bearings steel bearing environmental requirements must have diverse properties. The apparatus speed is increased, the need quasi-high temperature (less 200 ℃) bearing steel (commonly used to improve the content of Si on the basis of SUJ2 steel on adding V and methods of Nb to achieve the purpose of the softening-resistant and stable size); corrosion applications need to develop stainless steel bearing; to simplify the process, it should be developed and short high-frequency hardening bearing steel carburizing bearing steel; in order to meet the needs of the aerospace, high temperature bearing steel should be developed.