After compression spring rolling, recrystallization annealing treatment is required to stabilize the geometric shape of the spring and reduce quenching deformation. The recrystallization annealing temperature is 550-650 ℃, followed by air cooling after 1-1.5 hours. A small amount can be carried out in a salt bath furnace, while a large amount can be used to control the atmosphere in a continuous resistance furnace.
2) When quenching and heating in a salt bath furnace, the spring should be evenly tied with steel wire or heated on the core shaft. When heating, the surface of the spring should be decarburized with dinitrogen pentoxide. Deoxygenation should be carried out carefully in a salt bath. It can also be heated in a controlled atmosphere chamber furnace. Heating temperature 850 ℃± 10 ℃, keep warm for 10-15 minutes. The quenching oil is thoroughly cooled out of the oven.
3) After tempering and quenching, secondary tempering can be carried out. Firstly, the correct tempering temperature should be about 20 ℃ lower than the final tempering temperature of Z, kept for 10-15 minutes, and then air-cooled. Then perform final tempering, calibrate the spring, and install the spring on the tempering forming fixture for final tempering. The tempering fixture should meet the requirements for spring pitch and free length. Tempering temperature 420 ℃± 10 ℃, holding time 30-35 minutes.
4) Shot blasting is required to improve the fatigue strength of springs. The diameter of the projectile is 0.3-0.5mm. When using compressed air injection, the pressure of the compressed air is 0.4-0.5mpa; Adopting centrifugal shot blasting with a linear speed of 70m/s. After shot blasting treatment, the service life of compressed springs can be more than doubled.
The service life of compression springs should be considered both in use and in use. If the manufacturer consumes compression springs with a short lifespan and poor quality, then the compression spring manufacturer should consider this during the consumption process, which is also a customer interpretation. Usually, during use, we may shorten the lifespan of compression springs due to improper use. Below, we will introduce several methods to improve the service life of compression springs.
- Deformation heat treatment
Deformation heat treatment separates deformation strengthening and heat treatment strengthening, which can greatly improve the strength and durability of steel. Deformation heat treatment can be divided into high temperature and medium low temperature. High temperature deformation heat treatment can be quenched immediately after stable deformation in austenite state, or combined with forging or hot rolling, that is, quenched immediately after hot forming. By rapid tempering and high-temperature deformation heat treatment, the strength and fatigue life of automotive steel plate compression springs can be greatly improved.
- Isothermal quenching
Compression springs with small diameters or low hardenability can be selected for isothermal quenching, which can reduce the variation of dead points and further improve the strength and tolerance of the spring.
- Low temperature carburizing
For spiral compression springs, the combination of tempering and low-temperature carbonitriding (soft nitriding) significantly improves fatigue life and corrosion resistance.
- Eliminate the relaxation of compression springs
When a compression spring works for a long time under external force, it will undergo small deformation due to stress relaxation. Especially for compression springs, stress relaxation is more severe at high temperatures, and the accuracy of compression springs decreases, usually resulting in higher accuracy. Therefore, the compression spring should be relaxed after quenching and tempering. Heat treatment process: Stop preloading the compression spring to exceed the deformation that may occur during the operation of the compression spring. Then heat at an operating temperature above 20 for 8 to 24 hours.
- Shot blastingtreatment
Shot blasting is one of the commonly used methods to improve the appearance quality of compressed springs. Springs have high requirements for appearance quality. Scratches, creases, oxidation, decarburization and other external defects are often stress concentration centers and fatigue fracture sources during the operation of compression springs. If you use small steel shot to radiate the appearance of spring at high speed, it can not only strengthen shot blasting processing to improve the appearance quality of compressed springs, but also enhance the appearance strength of compressed springs. The appearance is in a state of compressive stress, which is useful for improving spring fatigue strength and daily life
