Answer
Spiral rings are manufactured by coiling cold-rolled flat wire. This cold-working increases the tensile strength through strain hardening, but it also leaves high levels of residual tensile stress on the outer diameter and compressive stress on the inner diameter. If the ring is used as-coiled, these stresses can lead to dimensional instability. Heat treatment (stress relieving or age hardening) allows the atoms to rearrange into a lower-energy state, 'locking' the ring into its coiled shape. For carbon steel, this is a tempering process; for 17-7PH, it is precipitation hardening. The resulting ring has a more uniform stress profile, which improves its resistance to fatigue and ensures that it maintains its 'cling' diameter over the life of the product.
