According to the forming method, the manufacturing of spring steel can be divided into cold forming and hot forming.
Due to its good impact toughness and surface compressive stress, the tendency of inner sleeve cracking during assembly, outer rib falling off and inner sleeve fragmentation during use is greatly reduced, and the edge stress concentration of roller can be reduced. Therefore, the average life and reliability of Austempering are higher than that of M quenching.
Heat treatment of thermoforming spring
The heating temperature is slightly higher than the quenching temperature. After heating, it is hot rolled, then quenched by waste heat, and finally tempered at 350 ~ 450 degrees to obtain tempered troostite structure. This is a thermomechanical treatment process, which can effectively improve the elastic limit and fatigue life. This method is generally used in large leaf springs of automobiles. For neutral coil spring, it can also be formed under cold condition, and then quenched and tempered.
Spring Factory suggests that in order to further develop the performance potential of spring steel, three points should be paid attention to in spring heat treatment: most spring steel is silicon manganese steel, silicon can promote decarburization, manganese can promote grain growth.
Therefore, the heating temperature, heating time and heating medium should be selected and controlled. If salt furnace is used for rapid heating and heating under protective atmosphere. Tempering should be carried out as soon as possible after quenching to prevent delayed fracture. Due to the high silicon content of spring steel, it is easy to produce graphitization in the process of annealing. The content of graphite is required to be inspected when the steel enters the factory. The tempering temperature is generally 350 ~ 450 ℃. If the steel surface is in good condition (e.g. after grinding), the low limit temperature tempering should be selected; otherwise, the upper limit temperature tempering can be used to improve the toughness of steel and reduce the sensitivity of surface defects.
Heat treatment of cold formed spring steel
Spring manufacturers remind you that for small springs, such as coil springs or spring steel strips with wire diameter less than 8 mm, they can be shaped after heat treatment or cold deformation, that is, cold drawing and cold rolling. The cold drawn steel wire has high strength, which is obtained by the work hardening of cold drawing deformed steel.
Quenching and tempering steel wire: this kind of steel wire is cold drawn to the final size, then hardened and tempered at medium temperature, and finally formed by cold rolling. The disadvantage of this kind of strengthening is that the process is more complicated and the strength is lower than that of lead quenched cold drawn steel wire.
In practice, it is found that the elastic limit of the steel wire which has been strengthened after cold rolling is not high, because the cold rolling forming will be easy to move into error, and the initial plastic deformation resistance will be reduced due to Bauschinger effect. Therefore, a low temperature tempering must be carried out after the cold roll forming, which has caused many changes and improved the elastic limit.