Spring steel is widely used in various equipment such as airplanes, railway vehicles, automobiles, tractors and other transportation tools and construction machinery. Spring steel should have excellent comprehensive properties, hoping to obtain higher mechanical properties (especially elastic limit, strength limit, yield ratio), elastic reduction performance (that is, elastic reduction resistance, also known as relaxation resistance), fatigue performance , Hardenability, physical and chemical properties (heat resistance, low temperature resistance, oxidation resistance, corrosion resistance, etc.). At the same time, from the perspective of energy saving and economy, the requirement to reduce the weight of springs to reduce the weight of vehicles, motorcycles and other transportation tools has also become an important aspect. Therefore, the development of high-strength spring steel is required. In recent years, a lot of research work has been carried out at home and abroad in order to further improve the strength level and service life of spring steel.
1 Main steel grades of spring steel at home and abroad
Chinese spring steel referred to the spring steel grades of the former Soviet Union in the 1950s. The main reason is that the Si-Mn series spring steel has the disadvantage of low hardenability. With the rapid development of the national economy, it can no longer meet the needs of China’s industrial development. After two revisions in 1977 and 1984, some useless grades were deleted and Cr-Mn spring steel with high hardenability was added. There are 15 steel grades of spring steel currently in production and used and listed in GB/T 1222-2007.
When American ASTM A 689 carbon steel and alloy steel bars for springs are classified according to their chemical composition, their standard steel numbers are AISI series 100, 4100, 5100, 6100, 8600 and 9200, and include AISI boron steel series 10B00, 15B00, 50B00 and 51B00. The specified steel grades can be found in ASTM A 322 and A 576, and the chemical composition of AISI steel grades can be adjusted to suit the special steel size, spring shape and other special requirements for permeability. For delivery according to hardenability, capital letter “H” should be added after steel grade. The standard alloy steel grades are AISI series and 4100H, 5100H, 6100H, 8600H and 9200H, as well as 50B00H and 51B00H including AISI boron series. For the specified steel grade, see standard ASTM A 304.
There are many types and quantities of spring steel in the United States, but the commonly used steel grades are 9260, 9254, 5160 and improved 5160, especially 5160(H) and 9260 which are the most widely used and the largest in output.
Nine steel grades are included in the Japanese spring steel standard JIS G4801. When JIS G4801 was revised in 1984, the spring steel SUP4 was deleted because it had no use value. SUP3 was only used as a supplement to the leaf spring of railway vehicles. Among the 8 alloy spring steel grades, SUP6 and SUP7 are Si-Mn steel, and high-silicon SUP7 is mainly used for high-stress suspension springs; SUP9 and SUP9A are Cr-Mn steel; compared with SUP9, it was taken from when the standard was revised in 1977 SUP9A of American steel grade SAE5160 has higher carbon, manganese, and chromium content and better hardenability, suitable for thicker suspension springs; SUP10 is Cr-V steel, which has good toughness and is suitable for use conditions Bad spring steel; SUP11A is a spring steel with boron treatment for SUP9, which has better hardenability and can be used for 35 mm thick springs; two new grades were introduced in the new standard in 1984; SUP12(SAE9254) It is Si-Cr steel with good tempering resistance and decarburization resistance. It is used for high-stress suspension springs; SUP13 (SAE4161) is Cr-Mo steel with very good hardenability and can be used for super large springs with a diameter of more than 60 mm. .
There are 6 steel grades in the German spring steel standard DIN 17221. Among them, 38Si7 is Si-Mn steel, 54SiCr6 and 56SiCr7 are Si-Mn-Cr steel, 55Cr3 is Cr-Mn steel, 50CrV4 is Cr-V steel, and 51CrMoV4 is added with a certain amount of Mo content on the basis of 50CrV4, which greatly improves It improves the hardenability and tempering stability of steel, and is suitable for manufacturing super-large springs that work in high-temperature environments.