Heat treatment of spring steel

Spring steel can be divided into hot forming spring and cold forming spring according to the different forming ways.

Heat treatment of thermoforming springs. Thermoforming springs are used to make springs of large or complex shapes. Generally, quenching heating is combined with forming. That is, the heating temperature is slightly higher than the quenching temperature (830℃~880℃), after heating, hot coil forming is carried out, and then the waste heat is quenched, and finally the moderate temperature tempering is carried out at 350℃~450℃, so as to obtain the tempered tretinite structure.

The surface quality of spring steel is very important because of its maximum torsional and bending stress. Surface decarburization is the most taboo, will greatly reduce the fatigue strength of steel. Therefore, the heating temperature, heating time and heating medium should pay attention to the selection and control. In addition, shot peening after tempering is also beneficial to eliminate surface defects such as decarburization, cracks, inclusions and markings, and strengthen the surface to form residual compressive stress and improve the fatigue strength of the spring.

Heat treatment of cold forming springs. Cold-formed spring steel is first after quenching, tempering treatment, or after isothermal quenching, and then through cold drawing to get high strength steel wire, and then use this steel wire directly to roll the required spring. This spring is no longer formed after quenching treatment, only a 180~370℃ low and medium temperature tempering, in order to eliminate the internal stress caused by forming. The cross-section size of this kind of spring steel is small, according to the quenching and tempering process before forming is divided into oil tempering steel wire and rapid isothermal treatment cold drawn steel wire. The former is oil quenching + moderate temperature tempering treatment; The latter refers to the lead bath (500~550℃) isothermal quenching to make the sotenite transformation, and then through several cold drawing strengthening.

If the spring wire diameter is too large, such as Φ> 15mm, plate thickness h> 8mm, there will be quench opaque phenomenon, resulting in the reduction of elastic limit, fatigue strength, so the spring steel hardenability must be adapted to the diameter of the spring material.


Post time: Mar-29-2023
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