Why is 'stress relieving' critical after the coiling of carbon steel wave springs?

Coiling wave springs from cold-rolled flat wire introduces significant residual tensile and compressive stresses throughout the cross-section. Without stress relieving, these internal stresses can cause 'creep' or dimensional instability over time. For SAE 1070-1090 carbon steel, stress relieving is typically performed at $600^{\circ}F$ to $700^{\circ}F$. This process stabilizes the microstructure, reduces the risk of stress corrosion, and ensures that the elastic properties are consistent. It also minimizes 'spring back' variations, allowing for tighter control over the free height $L_{free}$ and wave diameter.