3.4 Strengthening technology of spring

(1) Heat Treatment Strengthening Technology of Spring

1) Protective atmosphere heat treatment. In China, the heat treatment of springs with wire less than 15mm, oil-quenched and tempered steel wires and toughened steel adopts protective atmosphere heat treatment. Protective atmosphere heat treatment can eliminate surface decarburization and oxidation and improve the surface quality of materials.

2) Induction heating or protective atmosphere induction heating treatment. This process is usually carried out on the wire before the helical spring is formed. Some spring factories put the heat treatment of wire material and spring production together to reduce the cost. Induction heating treatment has a good reinforcing effect, and the induction heating speed is fast, which is conducive to refining the grain and reducing the surface decarbonization, and can give full play to and improve the strength and toughness of the material.

3) Surface nitriding heat treatment process technology. In recent years, in order to achieve reliable fatigue life of high stress valve spring or other high stress clutch spring, surface nitriding process technology is also adopted. At present, the advanced process is low-temperature gas nitriding technology. Generally, the nitriding temperature is 450~470 ℃, and the gas nitriding time is 5-20h.

(2) Shot peening process of spring

1) Combined shot blasting technology. Combined shot peening is generally called multiple shot peening process. Most economical processes use secondary shot blasting. This is achieved by using shot peening of different diameters. For the first time, larger shot size is used to obtain residual compressive stress and surface finish.

2) Stress peening process. The stress shot peening process is also a classic shot peening process, just because it is difficult to be used in mass production. But in recent years, due to the rapid development of the stress shot peening equipment, it has been widely used in the mass production of high stress automotive suspension springs. In particular, the combination of stress-reinforcing shot peening and other shot peening processes has a good reinforcing effect. The pre-stress of stress shot peening is generally set at 700~800MPa, and the peak value of residual stress can reach 1200~1500MPa after stress blasting, so as to obtain high fatigue strength.

(3) Hot pressing process of spring The hot pressing process is mainly applied to the spiral spring with high requirements for water resistance and deformation resistance, and it is an advanced stabilization process for water resistance and deformation resistance. In addition to significantly improving the resistance to water deformation
Improved fatigue life.