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What is bearing steel, and what is the material of bearing steel?

wallpapers Tech 2020-05-27
Bearing steel is used to make balls, rollers, and bearing rings. Bearings are subjected to extreme pressure and friction during operation, so bearing steels are required to have a high and uniform hardness and wear resistance, as well as upper elastic limits. The requirements for the uniformity of the chemical composition of bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are stringent. It is one of the most strict steel types in all steel production.
 
In 1976, the International Organization for Standardization (ISO) incorporated some common bearing steel grades into international standards and divided the bearing steel into four categories: fully hardened bearing steel, case hardened bearing steel, stainless bearing steel, and high temperature bearing steel. Steel number. Some countries add a type of bearing steel or alloy for particular purposes. The classification method of bearing steel that has been included in the standard in China is similar to ISO, corresponding to four categories of high-carbon chromium bearing steel, carburized bearing steel, stainless corrosion-resistant bearing steel, and high-temperature bearing steel.
 
In the past 50 years, China has also made significant progress in bearing steel grades and bearing materials, such as chromium-free bearing steel, medium carbon bearing steel, special-purpose bearing steel and alloys, cermets, etc. High-carbon chromium bearing steel GCr15 is the world's most significant production taking iron, with a carbon content of Wc of about 1% and a chromium content of War of about 1.5%. Since its birth in 1901 to more than 100 years, the main components have basically not changed. With the advancement of science and technology, research work continues, and product quality continues to improve, accounting for more than 80% of the world's total bearing steel production. So much so that the bearing steel we are talking about is GCr15 if there is no particular explanation.
 
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., the bearing steel should have: high hardness, uniform hardness, upper elastic limit, high contact fatigue Strength, necessary toughness, certain hardenability, corrosion resistance in atmospheric lubricants. In order to achieve the above performance requirements, strict requirements are imposed on the uniformity of the chemical composition of the bearing steel, the content and type of non-metallic inclusions, the particle size and distribution of carbides, and decarburization. Bearing steel is generally developed in the direction of 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 unique bearing materials according to characteristics and application environment.
 
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 unique properties. To reduce the oxygen content of bearing steel, bearing steel smelting technologies such as vacuum smelting, electroslag remelting, and electron beam remelting have been developed. The smelting of large quantities of bearing steel has been developed by electric arc furnace smelting, and it has been developed into various types of primary furnaces and refining outside the oven. At present, the bearing steel is produced by a central boiler 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 the heat treatment process, the vehicle bottom furnace and bell furnace have been developed into a continuously controlled atmosphere annealing furnace for heat treatment. At present, the most extended continuous heat treatment furnace type is 150m, the spheroidized structure of the bearing steel produced by processing is stable and uniform, the decarburization layer is small, and the energy consumption is low.
 
Since the 1970s, with the economic development and industrial, technological progress, the application range of bearings has expanded; and the development of international trade has promoted the internationalization of bearing steel standards and the development and application of new technologies, new processes and modern equipment. The supporting technology and process equipment with high quality, high quality, and the low cost came into being. Japan and Germany have built high-cleanliness and high-quality bearing steel production lines, which have rapidly increased steel output and greatly improved the quality and fatigue life of steel. The oxygen content of enduring steels produced in Japan and Sweden drops below ten ppm. In the late 1980s, the advanced level of Japan's Sanyo Special Steel Company was 5.4 ppm, which reached the level of vacuum remelted bearing steel.
 
The contact fatigue life of bearings is very sensitive to the uniformity of the steel structure. Improve cleanliness (reduce the content of impurity elements and inclusions in steel), promote the fine and even distribution of non-metallic inclusions and carbides in iron, and improve the contact fatigue life of bearing steel. The structure of the bearing steel in use should be tempered martensite matrix with fine carbide particles evenly distributed. Such an arrangement can give the bearing steel the required properties. The main alloying elements in high carbon bearing steel are carbon, chromium, silicon, manganese, vanadium, etc.
 
How to obtain the modular structure is an essential issue in the production of bearing steel, and controlled rolling and controlled cooling are critical production processes for advanced bearing steel. Through controlled rolling or rapid cooling after rolling, the network carbide is eliminated, and a suitable preparatory structure is obtained, which can shorten the spheroidizing annealing time of the bearing steel, refine the carbide, and improve the fatigue life. In recent years, Russia and Japan have adopted low-temperature controlled rolling (800 ℃ ~ 850 ℃ or less), after rolling using air cooling plus short-time annealing, or altogether cancel the spheroidizing annealing process; you can get a qualified bearing steel structure. The 650 ℃ warm processing of bearing steel is also a new technology. If the eutectoid steel or high carbon steel has a fine grain structure before thermal processing or can form fine grains during the processing, it will show superplasticity at a specific strain rate within the melting temperature range of (0.4 ~ 0.6). The United States Naval Research Institute (NSP) conducted a 650 ° C temperature processing test on 5 2100 steel and showed that at 650 ° C, the right strain 2.5 did not break. Therefore, it is possible to replace high-temperature processing with 650 ℃ temperature processing and combine it with the spheroidizing annealing process, which is of great significance for simplifying equipment and procedures, saving energy and improving quality.
 
In terms of heat treatment, progress has been made in improving the quality of spheroidizing annealing, obtaining fine, uniform, and spherical carbides, and shortening the annealing time or eliminating the spheroidizing annealing process. The recrystallization annealing after 720 ℃ ~ 730 ℃ was changed to 760 ℃ microstructure annealing. In this way, a structure with low hardness, good spheroidization, and no mesh carbide can be obtained. The critical point is to ensure that the standard drawing reduction rate is ≥14%. This process increases the efficiency of the heat treatment furnace by 25% to 30%. Continuous spheroidizing annealing heat treatment technology is the development direction of bearing steel heat treatment.
 
Countries are researching and developing new bearing steels, expanding applications, and replacing traditional bearing steels. For example, rapid carburizing bearing steel can improve the carburizing speed by changing the chemical composition. The carbon content is increased from conventional 0.08% to 0.20% to about 0.45%, and the carburizing time is shortened from 7 hours to 30 minutes. Developed high-frequency quenching bearing steel, using ordinary medium carbon steel or medium carbon-manganese, chromium steel, and replacing ordinary bearing steel by high-frequency heating quenching, which not only simplifies the production process but also reduces the cost and improves the service life. The fatigue life of GCr465 and SCM465 developed in Japan is 2 to 4 times higher than that of SUJ? 2. Due to the increasing use of bearings in environments with high temperatures, corrosion, and harsh lubrication conditions, bearing steels such as M50 (CrMo4V), 440C (9Cr18Mo), etc. used in the past cannot meet the requirements of use, and it is urgent to develop excellent processing performance, low cost, and fatigue Bearing steel with long life and suitable for different purposes and uses, such as high-temperature carburized steel M50NiL, easy-to-process stainless bearing steel 50X18M and ceramic bearing materials.
 
Aiming at the weakness of GCr15SiMn steel with low hardenability, 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 GCr15Si Mn, respectively. Under the same 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 that can save energy, resources, and impact. Compared with GCr15, the impact value of GCr4 is increased by 66% to 104%, the fracture toughness is increased by 67%, and the contact fatigue life L10 is increased by 12%. GCr4 steel bearings use high-temperature heating? Surface quenching heat-treatment process. Compared with fully hardened GCr15 steel bearings, the life of GCr4 steel bearings is significantly improved and can be used for heavy-duty high-speed train bearings.
 
From now on, bearing steel will mainly develop in two directions of high cleanliness and diversified performance. Improving the purity of the bearing steel, especially reducing the oxygen content in the steel, can significantly extend the life of the bearing. The oxygen content is reduced from 28ppm to 5ppm, and the fatigue life can be reached by order of magnitude. In order to extend the life of bearing steel, people have been devoted 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 28 ppm in the 1960s to 5 ppm in the 1990s. At present, China can control the minimum oxygen content in taking iron to about 10ppm. The changes in the use environment of the bearings require that the bearing steel must have diversified properties. If the speed of the equipment is increased, quasi-high temperature (below 200 ℃) bearing steel is needed (usually the method of increasing the Si content on the basis of SUJ2 steel, adding V and Nb to achieve the purpose of softening resistance and stable size); corrosion applications It is necessary to develop stainless bearing steel; in order to simplify the process, high-frequency quenched bearing steel and short-term carburized bearing steel should be developed; in order to meet the needs of aerospace, high-temperature bearing steel should be developed.
 
Bearing steel is used to make balls, rollers, and bearing rings. Bearings are subjected to extreme pressure and friction during operation, so bearing steels are required to have a high and uniform hardness and wear resistance, as well as upper elastic limits. The requirements for the uniformity of the chemical composition of bearing steel, the content and distribution of non-metallic inclusions, and the distribution of carbides are stringent, and it is one of the most strict steel types in all steel production. In 1976, the International Organization for Standardization (ISO) incorporated some common bearing steel grades into international standards and divided the bearing steel into four categories: fully hardened bearing steel, case hardened bearing steel, stainless bearing steel, and high temperature bearing steel. Steel number. Some countries add a type of bearing steel or alloy for particular purposes. The classification method of bearing steel that has been included in the standard in China is similar to ISO, corresponding to four categories of high-carbon chromium bearing steel, carburized bearing steel, stainless corrosion-resistant bearing steel, and high-temperature bearing steel. In the past 50 years, China has also made significant progress in carrying steel grades and bearing materials, such as chromium-free bearing steel, medium carbon bearing steel, special-purpose bearing steel and alloys, cermets, etc. High-carbon chromium bearing steel GCr15 is the world's most significant production taking iron, with a carbon content of Wc of about 1% and a chromium content of War of about 1.5%. Since its birth in 1901 to more than 100 years, the main components have basically not changed. With the advancement of science and technology, research work continues, and product quality continues to improve, accounting for more than 80% of the world's total bearing steel production. So much so that if we do not have special instructions for bearing steel, it means GCr15.

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