Research and development status of bearing steel in steel grade series and at h

Research and development status of bearing steel in steel grade series and at home and abroad

The quality of bearing steel is one of the strictest requirements and the most inspection items of the steel grades among all alloy steels. It is recognized in the world that the manufacturing level of bearing steel marks the metallurgical level of a country. With the increasing development of science and technology, the performance of bearing steel is constantly improving, and people's use conditions and requirements for bearing steel are becoming stricter and more demanding. Depending on the performance characteristics of the bearing, the use and working environment are different. Therefore, in addition to the mass-produced high-carbon chromium bearing steel, carburized bearing steel, medium-carbon bearing steel, stainless bearing steel, and high-temperature bearing steel have also been developed And series of steel grades such as nitrocarburizing and pure steel.

High-carbon chromium bearing steel is the most representative steel type of bearing steels, for which every country has its own special technical standards：

For example, included in the international standard ISO/FDIS683-17, the steel grades of high carbon chromium bearing steel are: 100Cr6, 100CrMnSi4-1, 100CrMnSi6-4, 100CrMnSi6-6, 100CrMo7, 100CrMo7-3, 100CrMo7-4, 100CrMnMoSi8-4- 6.

American material standard of ASTM A295 high carbon chromium bearing steel includes: 52100, 5195, UNSK19526, 1070M, 5160. In addition, the United States has another special standard ASTM A485 for high hardenability high carbon chromium bearing steel, which includes steel grades: Grade1~Grade4, 100CrMnSi4-4, 100CrMnSi6-4, 100CrMnSi6-6, 100CrMo7, 100CrMo7-3 , 100CrMo7-4, 100CrMnMoSi8-4-6.

The steel grades of high carbon chromium bearing steel (G B/T18254-2002) in the Chinese steel standard include: GCr15, GCr15SiMn, GCr4, GCr15SiMo, GCr18Mo.

The surface of carburized bearing steel has high hardness and high wear resistance after carburization, while the core still has good toughness and can withstand greater impact. The maximum service temperature of this type of steel is generally below 200°C. The output of this type of steel accounts for about 3% of the total output of bearing steel in China and about 30% in the United States. The carburized bearing steel grades in ISO/FDIS683-17 include 20Cr3, 20Cr4, 20MnCr4-2, 17MnCr5, 19MnCr5, 15CrMo4, 20CrMo4, 20MnCrMo4-2, 20NiCrMo2, 20NiCrMo7, 18CrNiMo7-6, and 16NiCrMo16-5.

In the American ASTM A534 carburizing steel standard, in addition to covering all the steel grades of ISO/FDIS683-17, it also includes: 4118H, 4320H, 4620H, 4720H, 4817H, 4820H, 5120H, 8617H, 8620H and 9310H.

The steel grades in China's carburized bearing steel standard GB/T3203-82 have: G20CrMo, G20CrNiMo, G20CrNi2Mo, G20Cr2Ni4, G10CrNi3Mo. After carburized, quenched and tempered, G20Cr2Mn2Mo steel has higher hardness of the surface layer and wears resistance, which meets the basic requirements of bearing materials. The hardness of the core is better, and has good toughness, which is suitable for making parts that can withstand impact load. In addition, it also has higher heat resistance; its performance is similar to that of the US 4118H. After carburizing or carbonitriding, G20CrNiMo steel has significantly better contact fatigue life than GCr15 steel. Its surface wear resistance is similar to that of GCr15 steel; its core has sufficient toughness. This steel also has good hardenability and good steel for making impact-resistant bearings，which performance is similar to that of US 8620H. G20CrNi2Mo steel, it has strong surface hardenability, and better hardenability and comprehensive mechanical properties than G20CrNiMo steel. It is suitable for making rings of rolling bearings for railway trains and also for making automobile gears. Its performance is similar to that of the US 4320H. After carburization the surface of G20Cr2Ni4 steel has high hardness, wear resistance and contact fatigue strength, at the same time it has good core toughness and can withstand strong impact loads. However, it is sensitive to the formation of white spots during use, and is prone to temper brittleness. It is suitable for making large-sized bearings resistant to impact loads. G10CrNi3Mo is a sort of surface carburizing steel with relatively high alloy content and high hardenability. Because of its low carbon content, the hardness of the core is not higher than 32~38HRC, and its performance is similar to the United States' 9310H.

The strength, plasticity, toughness and process properties of G20Cr2Mn2Mo steel are similar to those of G20Cr2Ni4 steel. The carburizing speed is fast and easy to reach saturation, and the carburized surface is easy to form coarse-grained carbides. It is mainly used for manufacturing large and medium-sized bearings working with high impact loads.

The development of medium-carbon bearing steel is mainly to meet the need of manufacturing bearings for hubs and gears, as well as bearing components or oversize bearings for multiple functions, and the steel is suitable for making extra-large bearings for heavy equipment such as tunneling, lifting, and large machine tools. Generally, the bearing’s speed is not high, but it bears large axial and radial loads and bending stresses, etc. It’s hot and cold working performance is better, and the heat treatment process is relatively simple compared with carburizing and carbonitriding treatment, and it also achieves the surface hardening effect. Therefore, it has been very popular in recent years. The medium carbon bearing steel grades included in the international standard ISO/FDIS683-17 are: C56E2 (equivalent to S55C or SAE1055), 56Mn4, 70Mn4 (equivalent to SAE1070), 43CrMo4 (equivalent to SCM440 or SAE4142). In the American medium carbon bearing steel standard ASTM A866 (2001), in addition to C56E2 and 56Mn4, there are: 1030, 1040, 1050, 1541, 1552, 4130, 4140, 4150, 5140, 5150, 6150 and 43CrMo4. After quenching and tempering, these medium carbon bearing steels have high yield strength ratio, high elastic limit and wear resistance, good fatigue resistance and frequent impact resistance. Among China's medium carbon alloy steels, the steel grades commonly used for medium carbon bearing steels are: 55, 50MnA, 70Mn, 37CrA, 65Mn, 50CrVA or 50CrNi, 55SiMoVA, 50SiMo, 50CrNiMo or SAE8660.

The stainless bearing steel developed to meet the needs of chemical, petroleum, shipbuilding, food industry, etc., is mainly used to manufacture bearings and certain parts that work in corrosive environments. It can also be used to manufacture low-friction, low-friction, miniature precision bearings with low torque. Stainless bearing steel mainly includes: medium and high carbon martensitic stainless steel, austenitic stainless steel, precipitation hardening stainless steel and so on. In order to meet the hardness requirements of bearings, martensitic stainless steel is often used.

The stainless bearing steel grades accepted in ISO/FDIS683-17 are: X47Cr14, X65Cr14, X108CrMo17 (equivalent to ASTM440C), X90CrMoV18-1. The stainless bearing steels in the American standard ASTM A756 are: 440C and 440CMOD. China's stainless steel bearing steel GB3086 standard steel grades are 9Cr18 (equivalent to ASTM440C) and 9Cr18Mo.

With the rapid development of the aviation and aerospace industries, the requirements for manufacturing bearings used in jet engines, gas turbines and aerospace vehicles are getting higher and higher, and the working temperature of bearings is getting higher and higher, even higher than 300℃. In this way, high-temperature bearing steel suitable for demand came into being. The characteristics of these high temperature bearing steels are: high temperature hardness (greater than 50HRC) and dimensional stability, high temperature oxidation resistance, low thermal expansion and high –anti creep strength，of which the first two are the main indicators for selecting high-temperature bearing steel materials. High temperature bearing steel is divided into: high temperature stainless bearing steel, high temperature high speed tool steel and high temperature carburizing bearing steel. The steel grades of high temperature bearing steel included in ISO/FDIS683-17 are: 80MoCrV42-16, X82WmoCrV6-5-4, X75WCrV18-4-1. Steel grades such as T1, M2, and M50 in the American high-speed tool steel ASTM A600 (1999) standard can be used as high-temperature bearing steel. The steel grades in China's high temperature bearing steel standard GB3086 are: 8Cr4Mo4V and 10Cr14Mo4. 8Cr4Mo4V is a high-temperature stainless steel containing molybdenum (Mo), which is equivalent to M50 steel in the ASTMA600 standard. M50 steel is also a high-temperature bearing steel widely used in various countries. , It has good high-temperature hardness and high-temperature dimensional stability, and has high-temperature contact fatigue resistance. It is used to manufacture bearings whose working temperature is below 315℃. These bearings are mainly used for aircraft, naval engines, as well as for medium and high temperature equipment in metallurgy, chemical and atomic energy industries. 10Cr14Mo4 steel is an improved steel grade of 9Cr18Mo. It increases the content of Mo and reduces the content of Cr, which improves the high temperature hardness and wear resistance, and the service temperature can reach 480℃. The steel grades of high-speed tool steel in China's high-temperature bearing steel series include Cr4Mo4V and W18Cr4V. The former is equivalent to M50 in the United States. It is widely used because of its excellent comprehensive performance and low alloying element content. It is equivalent to 10Cr14Mo4 in terms of wear resistance, high temperature hardness and oxidation resistance. As an intermediate high temperature bearing steel, it can be used for manufacturing bearings that working below 315°C. The latter, which are equivalent to T1 in ASTMA600, are suitable for bearings that work at higher temperatures and higher hardness conditions.