Official Answer
Answer
Stress relieving is a thermal process performed after coiling to stabilize the spring's geometry. During cold coiling, significant residual stresses are introduced into the material. Without stress relieving, these stresses can cause the spring to relax or 'creep' over time, leading to a loss of free height and reduced load at the working height. For carbon steel, stress relieving occurs at $450^{\circ}F-500^{\circ}F$. For 17-7PH, the precipitation hardening at $900^{\circ}F$ also acts as a stress relief. This process 'sets' the waves, ensuring that the spring rate $k$ remains constant throughout its service life. Skipping this step in a high-precision application will result in 'load loss' and potential assembly loosening.
