1)Deformation heat treatment- -Combine the deformation strengthening and heat treatment strengthening of the steel , to further improve the strength and toughness of the steel. Thermomechanical heat treatment is divided into high, medium and low temperature. High temperature thermomechanical heat treatment is quenched immediately after deformation occurs in a stable austenite state. , can also be combined with forging or hot rolling , that is, quenched immediately after hot forming. Thermomechanical treatment has been used in the production of automobile leaf springs. (60Si2Mn) 
(2)Austempering of spring--For springs with small diameter or sufficient permeability, austempering can be used, it can not only reduce deformation >, And it can also improve the strength and toughness, It is best to perform tempering after austempering, can increase the elastic limit, >The tempering temperature is the same as the austempering temperature.  
(3)Relaxation of the spring--The spring works under the action of external force for a long time,As a result of stress relaxation, a small amount of permanent ( Plastic)Deformation,Especially the spring working at high temperature,The stress relaxation phenomenon is more serious at high temperature,< /span>Reduce the accuracy of the spring , This is not allowed for general precision springs. Therefore, , such springs should be relaxed after quenching , after tempering -- preload the spring , Make the amount of deformation exceed the amount of deformation that may occur when the spring is working. Then heat , heat preservation 8-24h under the condition of 20C higher than the working temperature.  
(4)Low temperature carbonitriding -- adopts tempering and low temperature carbonitriding (nitrocarburizing) phase The combined process , can significantly improve the fatigue life and corrosion resistance of the spring. , This process is mostly used for coil springs.  
(5)Shot peening treatment --Surface defects such as scratches, folding, oxidative decarburization, etc. often become stress concentration places and sources of fatigue fracture during spring operation. If small steel shots are used to spray the surface of the spring at high speed , not only improves the surface quality of the spring , increases the surface strength , and makes the surface in a state of compressive stress , to improve the fatigue strength and service life of the spring.  
Operation precautions 
(1) Check the surface for defects such as decarburization and cracks before heat treatment. These surface defects will severely reduce the fatigue limit of the spring.  
(2)Quenching heating should pay special attention to prevent overheating and decarburization, do a good job in salt bath deoxidation, control the furnace gas atmosphere Strictly control heating temperature and time 
(3) In order to reduce the deformation , the method of loading the spring during heating , the form of fixture and the cooling method of quenching during cooling.  
(4) Tempering as soon as possible after quenching , heating should be as even as possible. Quick cooling after tempering can prevent temper brittleness and cause surface compressive stress , to improve fatigue strength.  
Quality check 
Before heat treatment--
(1) The rolled surface of the steel is often the surface after the spring is made , so there should be no cracks, folds, scars, hair lines, bubbles, interlayers, and pressed oxidation Pi etc.
(2) Surface decarburization will significantly reduce the fatigue strength of the spring. , The depth of the decarburized layer should be inspected as required.
After heat treatment--
(1) There should be no cracks, corrosion pits and severe quenching deformation when observing the spring watch with the naked eye or a low-power magnifying glass.
(2)The hardness and its uniformity meet the requirements. In mass production, , is allowed to use a file to sample the hardness ,, but it must be noted that the position of the file mark should not affect the final accuracy of the spring.
(3) The metallographic structure should be troostite or a mixed organization of troostite and sorbite.
(4)After the leaf spring is assembled , usually permanent deformation under working load and static load deflection test