Spring steel quenching defects appear in the following four main：
The steel deformation strengthening and heat treatment strengthening of the two combined to further improve the strength and toughness of steel. Deformation heat treatment has high, medium and low temperature. High-temperature deformation heat treatment is in the austenitic state of the deformation immediately after quenching, can also be combined with forging or hot rolling, that is, hot forming immediately after quenching. Deformation heat treatment has been applied to the production of automotive springs.
For a small diameter or permeability enough spring can be used isothermal quenching, it can not only reduce deformation, but also improve the toughness, isothermal quenching is best after a tempering, can improve the elastic limit, tempering temperature and isothermal quenching temperature the same.
Spring work for a long time under the action of external forces, as a result of stress relaxation will produce a small amount of permanent (plastic) deformation, especially the high temperature work of the spring, stress relaxation phenomenon is more serious at high temperatures, so that the accuracy of the spring is reduced, which is not allowed for the general precision spring. Therefore, this type of spring in the quenching, tempering should be relaxed after processing – the spring preload, so that the deformation of the spring may exceed the amount of deformation generated when working. Then heated under conditions higher than the working temperature of 20C, holding 8-24h.
The combination of tempering and low-temperature carbonitriding (nitrocarburizing) process can significantly improve the fatigue life of the spring and corrosion resistance, this process is mostly used for coil springs.
Scratches, folding, oxidation decarburization and other surface defects will often become the spring work where the stress is concentrated and fatigue fracture sources. If the spring surface with fine steel shot at high speed, not only improve the surface quality of the spring, improve the surface strength, and make the surface in a state of compressive stress, thereby improving the spring fatigue strength and service life.