Spring steel refers to special alloy steel used to manufacture various types of springs and other elastic components. According to performance requirements and usage conditions, it can be divided into ordinary alloy spring steel and special alloy spring steel.
According to its basic performance and usage characteristics, spring steel belongs to mechanical structural steel; according to its quality grade, it belongs to special quality steel, that is, steel that requires particularly strict quality and performance control during the production process. According to Chinese custom, spring steel is a special steel. The technical requirements for making spring steel are relatively high. Excellent technology directly determines the quality.
Spring is an important part in various machines and instruments. Its function is to convert mechanical work or kinetic energy and deformation energy into each other by relying on the elasticity of the material and the spring structure.
Spring mainly works under dynamic load, that is, under impact, vibration conditions or alternating stress, and plays the roles of support, vibration reduction, buffering, measurement, control, storage and output of energy. The main form of spring failure is fatigue fracture.
No matter where the spring is used, it is always in the process of deformation – recovery – deformation – recovery again, and no permanent deformation is allowed. Therefore, the spring should have high fatigue performance. Springs working in water, steam, oil, salt or alkali media should also have heat resistance and corrosion resistance. Some springs for special purposes are also required to have good electrical conductivity and non-magnetic properties. In order to ensure that the spring works reliably, spring steel must have the following basic performance requirements:
1) It must have high yield limit and elastic limit, especially a high yield-strength ratio, to avoid plastic deformation of the spring under high load.
2) It has a high fatigue limit to avoid fatigue damage of the spring under long-term vibration and alternating stress.
3) It has sufficient impact toughness and plasticity to prevent sudden brittle fracture under impact.
4) It has good surface quality. Any small rust, pits, bruises, decarburization, etc. may become the origin of fatigue fracture.
5) Spring steel should have good hardenability and low overheating sensitivity.
6) Springs for special purposes also have special requirements. For example, springs in electrical instruments are required to have high conductivity; springs working in high temperature or corrosive media are required to be resistant to high temperatures or corrosion.
Carbon steels include 65, 70, 85, etc., with a carbon content of 0.6% to 0.9% (mass fraction), and have high elastic limit and strength. Its disadvantages are poor hardenability, poor stress relaxation resistance, poor corrosion resistance, and large temperature coefficient of elastic modulus.
It is mostly used for springs with steel cross-sections less than 10 mm and low operating temperatures.
The most commonly used manganese steel is 65Mn. Compared with carbon spring steel, it has higher hardenability and strength, less decarburization tendency, but greater overheating tendency. It is generally used for small and medium-sized low-stress springs with a cross-section less than 15 mm.
Adding silicon to manganese steel can significantly improve the yield strength and tempering resistance stability of the steel. Commonly used silicon-manganese spring steels include 55Si2Mn and 60Si2Mn. In order to further improve the performance of silicon-manganese steel, trace amounts of boron and vanadium are added to the steel, such as 55Si2MnB, 55SiMnVB steel, etc., to obtain better comprehensive mechanical properties after heat treatment.
Silicon chromium steel and silicon chromium vanadium steel have 60Si2CrA, 60Si2CrVA, etc., with good hardenability, small tendency to overheat, and stable mechanical properties when working at high temperatures, can be used to manufacture large coil springs and plate springs that bear heavy loads and impact loads below 350℃.
Chromium manganese spring steel 55CrMnA, 60CrMnA, etc., has a higher elastic limit and strength than 65Mn steel. However, it has the disadvantage of overheating sensitivity and easy to produce tempering brittleness. The 60CrMnMoA spring steel containing molybdenum, its hardenability, strength, plasticity and high temperature strength are improved, the tendency of overheating and tempering brittleness is reduced, and can be used to manufacture plate springs with high loads and larger stresses and helical springs with larger spiral diameter (50 mm). It can also be used as valve springs and piston springs with operating temperatures below 300 ° C.
Chromium vanadium steel includes 50CrVA steel, etc. This steel has high elasticity and fatigue limits and can be used to manufacture particularly important coil springs of various sizes that can withstand large stresses, as well as important springs with large cross-sections and operating temperatures below 300°C.
Tungsten chromium vanadium steel includes 30W4Cr2VA steel, which is a high-strength, heat-resistant spring steel with particularly high hardenability. After quenching at 1050~1100℃ and tempering at 550~650℃, the tensile strength can reach 1500~1700 MPa. This steel is mainly used to make springs used at high temperatures below 540°C.
1) The cold-drawn spring steel processed by quenching lead is generally small springs such as high-stress springs with a diameter of less than 6 mm and valve springs, and the cold-drawn spring steel wire is used. In order to make the steel have high plasticity and good strength before cold drawing, it is fully austenized above Ac3 and quenched by constant temperature lead bath to obtain high plastic sorbite. After a number of cold drawing strengthening to obtain a high strength. The cold-drawn spring wire treated with quenched lead can be directly coiling the spring. After the spring is rolled, it is no longer quenched, but only needs to be fixed or de-stressed at low temperature.
2) Cold-drawn spring steel that is annealed in the middle is cold-drawn several times and annealed (to improve plasticity) in the middle of multiple cold-drawn spring steel for the manufacture of low-stress springs with a diameter of less than 13 mm. This kind of cold-drawn spring steel wire, after many cold strengthening, spring forming, only need to be held at 200 ~ 300℃ for 20 ~ 30 minutes of low temperature tempering, you can eliminate stress, improve the strength limit and stable size, or do not carry out any heat treatment.
3) The delivery state is oil quenched and tempered spring steel. This type of spring steel material has been quenched and medium-temperature tempered after cold drawing by the metallurgical enterprise, so after the spring is formed, it only needs to be stabilized at low temperature. If the spring needs to be corrected after tempering, the correction stress should be eliminated at a temperature 10 to 20°C lower than the tempering temperature.
4) Cold-drawn spring steel without quenching Cold-drawn spring steel without quenching, such as 60Si2MnA, 50CrVA and other cold-drawn alloy spring steel wires, are heat treated in the same way as hot-rolled steel after the spring is formed.
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