Several methods to improve the service life of medical spring

With the increase of industrial products, spring products are more and more rich, the number of springs gradually increased, spring related technology is gradually mature. How to improve the life of spring is a problem that spring manufacturers must face.

(1) Deformation heat treatment

Deformation heat treatment is the combination of deformation strengthening and heat treatment strengthening to further improve the strength and toughness of steel. Deformation heat treatment can be divided into three stages: high temperature, medium temperature and low temperature. High temperature deformation heat treatment in stable austenite state can be quenched immediately after deformation, or can be combined with forging or hot rolling, that is, quenched immediately after hot forming. After high temperature deformation heat treatment (930℃+ 18% thermal variable, oil quenching), the strength and fatigue life of automotive leaf springs made of 60Si2Mn steel are greatly improved under rapid tempering at 650℃×3.25min.

(2) spring isothermal quenching

For springs with small diameter or sufficient hardenability, isothermal quenching can be used, which can not only reduce the change of heart, but also improve the strength and toughness. It is best to temper again after isothermal quenching, which can improve the elastic limit. The tempering temperature is the same as that of isothermal quenching.

(3) Shot peening

Shot peening is one of the most widely used methods to improve the surface quality of spring. The spring requires a high surface quality, scratches, folding, oxidation and decarbonization surface defects often become the place of stress concentration and fatigue fracture source when the spring is working. If the small steel shot is sprayed at high speed on the surface of the spring, the shot peening treatment can not only improve the surface quality of the spring, improve the surface strength, so that the surface is in the state of compressive stress, so as to improve the fatigue strength and service life of the spring.

(4) relaxation of the spring

Spring for a long time under the action of external force, due to stress relaxation, will produce a trace of permanent (plastic) deformation, especially the high temperature work of the spring, at high temperature stress relaxation phenomenon is more serious, so that the accuracy of the spring is reduced, which is not allowed for general precision spring. Therefore, this kind of spring should be relaxed after quenching and tempering. Heat treatment process: the spring is pre-loaded so that its deformation exceeds the possible deformation of the spring when it is working. Then, it is heated at a temperature 20℃ higher than the working temperature and kept for 8~24h.

(5) Low temperature carbonnitriding

Tempering combined with low temperature carbonnitriding (soft nitriding) can significantly improve the fatigue life and corrosion resistance of the spring.