What is the tempering temperature and time control range of stainless steel torsion tension spring after forming

As a key mechanical elastic element, the performance of stainless steel torsion tension spring is directly related to the reliability and service life of mechanical equipment. Tempering after the forming process is one of the core steps to ensure the stability of the mechanical properties of the spring. Reasonable tempering temperature and time control are of great significance to eliminate processing residual stress, improve spring fatigue life and mechanical properties.

The role and necessity of tempering
Tempering is a heat treatment process after spring forming. The main purpose is to eliminate the residual stress generated during cold processing (such as stretching and torsion forming). The existence of residual stress will lead to unstable spring dimensions, fluctuations in mechanical properties, and even premature fatigue fracture. In addition, tempering can also improve the toughness of the material, reduce brittleness, and improve the fatigue resistance of the spring under repeated loading.
For stainless steel materials, especially commonly used austenitic stainless steels such as 304 and 316, tempering helps to stabilize its organizational structure, prevent material performance degradation after cold working hardening, and ensure that the elastic modulus and strength of the spring meet the design requirements.

Stainless steel spring tempering temperature range
The tempering temperature of stainless steel torsion tension springs is usually controlled between 350℃ and 550℃. The specific temperature selection varies according to the stainless steel grade, forming process and application environment of the spring.
350℃ to 400℃: Suitable for springs with light cold processing, which can effectively release the stress of work hardening, avoid excessive grain growth of the material, and maintain high strength and hardness.
400℃ to 450℃: This is the most common tempering temperature range, taking into account the elimination of residual stress and the optimization of mechanical properties. Most 304 and 316 stainless steel springs are tempered in this temperature range to ensure that the spring has good fatigue life and dimensional stability.
450℃ to 550℃: Suitable for springs or special alloy materials in high stress state. Higher temperature tempering can further improve toughness and reduce brittleness, but too high temperature may reduce the elastic modulus of the spring.
If the tempering temperature is too low, it is difficult to fully eliminate residual stress and affect the stability of spring performance; if the temperature is too high, it may cause the spring strength to decrease and the elastic performance to be damaged, affecting its normal use.

Control standard of tempering time
The tempering time is usually determined according to the size, wire diameter and material thickness of the spring, generally between 15 minutes and 60 minutes.
For springs with fine wire diameter (less than 1.0mm), the tempering time is mostly controlled at 15 to 30 minutes to avoid excessive annealing of the material due to too long a time.
Springs with medium wire diameter (1.0mm to 3.0mm) are generally tempered for 30 to 45 minutes to ensure that stress is completely released while maintaining the hardness and strength of the material.
Springs with larger wire diameters or thicker thicknesses require 45 to 60 minutes to ensure that heat is evenly transferred to the inside of the spring and the residual stress is fully eliminated.
Insufficient tempering time may cause the residual stress inside the spring to not be completely released, and dimensional changes or early fatigue fractures may occur in subsequent use. Too long a time may affect the hardness and elastic modulus of the material and reduce the load-bearing capacity of the spring.

Temperature uniformity and atmosphere control during tempering
Temperature uniformity during tempering directly affects the performance of the spring. A high-precision temperature-controlled furnace is used to ensure that the spring is heated evenly throughout the entire workpiece volume to avoid local overheating or temperature gradients that cause stress concentration.
The tempering environment is usually air or a protective atmosphere (such as nitrogen or argon). Protective atmosphere can effectively prevent high temperature oxidation and surface decarburization, keep the spring surface smooth and the material corrosion resistant. For springs in the medical and electronic industries with high requirements, protective atmosphere tempering is a common process choice.

The importance of performance testing after tempering
After tempering, a series of performance tests must be performed to ensure that the spring meets the design requirements. Common tests include spring stiffness test, dimensional stability test, fatigue life test and surface hardness test. Through testing feedback whether the tempering process is appropriate, the temperature and time control can be further optimized.
Fatigue life test is particularly important. After reasonable tempering, the fatigue performance of stainless steel springs is significantly improved, which can meet the requirements of high-cycle cyclic loads and adapt to complex mechanical environments.