Spring strengthening technology
(1) Spring heat treatment strengthening technology
1) Heat protection atmosphere. In China, heat treatment with a protective atmosphere is applied to the heat treatment of springs with a wire diameter of less than 15 mm, oil quenched and tempered steel wires, and toughened steels. The protective atmosphere heat treatment can eliminate surface decarburization and oxidation and improve the surface quality of the material.
2) Induction heating or protective atmosphere induction heat treatment. This process is generally performed on wire prior to the formation of coil springs, and some spring plants place the heat treatment of the wire material and springs together to reduce costs. The induction heating treatment has a good strengthening effect, and the induction heating speed is high, which helps to refine grains and reduce surface decarburization, and can fully exert and improve the strength and toughness of the material.
3) Surface nitrided heat treatment process technology. In recent years, in order to achieve a reliable fatigue life, high-stress valve springs or other high-stress clutch springs also employ surface nitriding technology. Nowadays, the more advanced technology is low-temperature gas nitriding technology, and the general nitriding temperature is (450-470). °C, gas nitriding time is (5 ~ 20) h.
(2) Spring shot peening process
1) Combined shot peening technology. Combined shot peening is also commonly referred to as multiple shot peening. Most economical processes use secondary shot peening. This is achieved by shot peening with different diameter pellets. Larger pellets were used for the first time to obtain residual compressive stress and surface finish.
2) Stress shot peening process. The stress shot peening process is also a classic shot peening process, but because it is difficult to apply to mass production, in recent years due to the rapid development of stress shot peening equipment, it has been obtained in large batch production of high stress automotive suspension springs. development of. In particular, the combination of stress-strengthening shot peening and other shot peening techniques has a very good strengthening effect. The prestress of stress shot peening is generally set at (700-800) MPa. After stress shot blasting, the peak value of residual stress can reach (1200-1500) MPa, resulting in high fatigue strength.
(3) Hot-pressing process of the spring The hot-pressing process is mainly applied to spiral springs with high requirements for permanent deformation, and it is used as a high-precision anti-permanent deformation stabilization process. In addition to a significant increase in resistance to permanent deformation, the hot-forcing process can also increase fatigue life.