Development direction of the hottest bearing steel

2022-08-17
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Development direction of bearing steel

bearing steel is mainly used to manufacture rolling elements and rings of rolling bearings. Because the bearing should have the characteristics of long life, high precision, low calorific value, high speed, high rigidity, low noise, high wear resistance, etc., it is required that the bearing steel should have: high hardness, uniform hardness, high elastic limit, high contact fatigue strength, necessary toughness, certain hardenability, corrosion resistance in atmospheric lubricants. In order to meet the above performance requirements, the uniformity of chemical composition, the content and type of non-metallic inclusions, the particle size and distribution of carbides, decarburization and other requirements of bearing steel are strict. Bearing steel is generally developing towards high quality, high performance and multiple varieties. Bearing steel is divided into high carbon chromium bearing steel, carburized bearing steel, high temperature bearing steel, stainless bearing steel and special bearing materials according to its characteristics and application environment

in order to meet the requirements of high temperature, high speed, high load, corrosion resistance and radiation resistance, it is necessary to develop a series of new bearing steels with special properties. In order to reduce the oxygen content of bearing steel, the smelting technologies of bearing steel such as vacuum smelting, electroslag remelting and electron beam remelting have been developed. The smelting of large quantities of bearing steel has developed from electric arc furnace smelting to various types of primary smelting furnaces plus external refining. At present, bearing steel is produced by primary smelting furnace with a capacity of more than 60 tons + LF/VD or Rh + continuous casting + continuous rolling process to achieve the purpose of high quality, high efficiency and low energy consumption. In terms of heat treatment process, the car bottom furnace and bell type furnace have been developed into continuous controllable atmosphere annealing furnace for heat treatment. At present, the longest continuous heat treatment furnace is 150m. The spheroidized structure of bearing steel processed and produced is stable and uniform, with small decarburization layer and low energy consumption

since the 1970s, with the economic development and industrial technological progress, the application range of bearings, taking North America as an example, has expanded; The development of international trade has also promoted the internationalization of bearing steel standards and the development and application of new technologies, new processes and new equipment. Supporting technologies and process equipment with high efficiency, high quality and low cost came into being. Japan and Germany have built high-purity and high-quality bearing steel production lines under the condition of ensuring the physicochemical properties of PPC, which has rapidly increased the output of steel and greatly improved the quality and fatigue life of steel. The oxygen content of bearing steel produced in Japan and Sweden fell below 10ppm. In the late 1980s, the advanced level of yamayo special steel company in Japan was 5.4ppm, which reached the level of vacuum remelted bearing steel

the contact fatigue life of bearing is very sensitive to the uniformity of steel structure. Improving cleanliness (reducing the content of impurity elements and inclusions in steel) and promoting the fine and uniform distribution of non-metallic inclusions and carbides in steel can improve the contact fatigue life of bearing steel. The structure of the bearing steel in use should be that fine carbide particles are evenly distributed on the tempered martensite matrix, which can give the bearing steel the required properties. The main alloy elements in high carbon bearing steel are carbon, chromium, silicon, manganese, vanadium, etc

how to obtain spheroidized structure is an important problem in the production of bearing steel, and controlled rolling and controlled cooling is an important production process of advanced bearing steel. The spheroidizing annealing time of bearing steel can be shortened, the carbides can be refined and the fatigue life can be improved by controlling rolling or rapid cooling after rolling. In recent years, Russia and Japan adopt low-temperature controlled rolling (below 800 ℃ ~ 850 ℃), air cooling and short-time annealing after rolling, or completely abolish the spheroidizing annealing process, which can obtain qualified bearing steel structure. 650 ℃ warm processing of bearing steel is also a new technology. If eutectoid steel or high carbon steel has fine grain structure before hot processing or can form fine grains during processing, it will show superplasticity at a certain strain rate within the melting temperature range of (0.4 ~ 0.6). The 650 ℃ warm working test of 52100 steel carried out by the Naval Research Institute (NSP) shows that the true strain of 2.5 does not fracture at 650 ℃. Therefore, it is possible to replace high-temperature processing with 650 ℃ temperature processing and combine it with spheroidizing annealing process, which is of great significance to simplify equipment and processes, save energy and improve quality

in terms of heat treatment, progress has been made in improving the quality of spheroidizing annealing, obtaining fine, uniform and spherical carbides, shortening the annealing time or canceling the spheroidizing annealing process, that is, twice structural annealing is used in wire rod production, and the recrystallization annealing after drawing is changed from 720 ℃ ~ 730 ℃ to 760 ℃. In this way, the structure with low hardness, good spheroidization and no shaped carbide can be obtained. The key is to ensure that the surface reduction rate of intermediate drawing is ≥ 14%. This process increases the efficiency of the heat treatment furnace by 25% - 30%. Continuous spheroidizing annealing heat treatment technology is the development direction of bearing steel heat treatment

all countries are researching and developing new bearing steel, expanding the application and replacing the traditional bearing steel. For example, the rapid carburizing bearing steel can improve the carburizing speed by changing the chemical composition, in which the carbon content is increased from the traditional 0.08% - 0.20% to about 0.45%, and the carburizing time is shortened from 7 hours to 30 minutes. High frequency quenching bearing steel is developed. Ordinary medium carbon steel or medium carbon manganese and chromium steel is used to replace ordinary bearing steel by high frequency heating quenching, which simplifies the production process, reduces the cost, and improves the service life. The fatigue life of gcr465 and scm465 developed in Japan is 2 ~ 4 times higher than that of suj-2. As more and more bearings are used in environments with high temperature, corrosion and poor lubrication conditions, bearing steels such as M50 (crmo4v) accounting for 15.56% and 440C (9Cr18Mo) used in the past can no longer meet the use requirements. There is an urgent need to develop bearing steels with good processing performance, low cost, long fatigue life and suitable for different purposes and uses, such as high-temperature carburized steel m50nil, easy to machine stainless bearing steel 50x18m and ceramic bearing materials

aiming at the weakness of low hardenability of GCr15SiMn steel, China has developed high hardenability and hardenability bearing steel gcr15simo, with hardenability HRC ≥ 60 and hardenability J60 ≥ 25mm. The contact fatigue life L10 and L50 of gcr15simo are 73% and 68% higher than that of gcr15si Mn respectively. Under the same service conditions, the service life of bearings made of g015simo steel is twice that of gcr15simo steel. In recent years, China has also developed GCr4 bearing steel, which can save energy, resources and impact resistance. Compared with GCr15, the impact value of GCr4 is increased by 66% - 104%, the fracture toughness is increased by 67%, and the contact fatigue life L10 is increased by 12%. GCr4 steel bearing adopts high temperature heating surface quenching heat treatment process. Compared with the fully quenched GCr15 steel bearing, the service life of GCr4 steel bearing is significantly improved, and it can be used for heavy-duty high-speed train bearings

in the future, bearing steel will mainly develop in two directions: high cleanliness and diversified performance. Improving the cleanliness of bearing steel, especially reducing the oxygen content in the steel, can significantly prolong the service life of bearings. When the oxygen content is reduced from 28ppm to 5ppm, the fatigue life can be extended by an order of magnitude. In order to prolong the service life of bearing steel, people have been committed to developing and applying refining technology to reduce the oxygen content in steel for many years. Through unremitting efforts, the minimum oxygen content in bearing steel has been reduced from 28ppm in the 1960s to 5ppm in the 1990s. At present, China can control the minimum oxygen content in bearing steel at about 10ppm. The change of bearing service environment requires that bearing steel must have diversified properties. For example, the increase of equipment speed requires quasi high temperature bearing steel (below 200 ℃) (usually the method of increasing Si content and adding V and Nb on the basis of SUJ2 steel is adopted. 2. The correction of force value on the criterion should be performed by the customer service department of the testing machine manufacturer or the measurement unit recognized by the state. If the user makes self-tuning and poses quality problems, the manufacturer will not bear it to achieve the purpose of anti softening and stabilizing the size); Corrosion applications require the development of stainless bearing steel; In order to simplify the process, high-frequency quenched bearing steel and short-time carburized bearing steel should be developed. (end)

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