How do we account for the work hardening of 17-7PH stainless steel when calculating spring relaxation?

17-7PH (Type 631) stainless steel achieves its properties through a combination of cold reduction and precipitation hardening. When designing for high-temperature environments, the relaxation or 'set' is influenced by the heat treatment condition (e.g., CH900). Relaxation is modeled by the Arrhenius equation where the rate of creep is $\epsilon = A \sigma^n e^{-Q/RT}$. For a wave spring, stress $\sigma$ must be kept below 75% of the minimum tensile strength of the CH900 condition ($210-240$ ksi) to minimize permanent set. If the operating temperature exceeds $650^{\circ}F$ ($343^{\circ}C$), the material undergoes significant loss of elastic modulus, and the design must be derated by approximately 5-10% to account for thermal relaxation.