Answer
17-7PH (UNS S17700) is a semi-austenitic precipitation-hardening stainless steel that provides high strength and corrosion resistance. In condition CH900, the material is cold-reduced to Condition C and then age-hardened at $900^{\circ}F$ ($482^{\circ}C$). This process transforms the austenite to martensite through cold work and then precipitates an aluminum-rich intermetallic phase. The resulting yield strength typically exceeds $200$ ksi. For wave springs, this high elastic limit allows for significant deflection without permanent set. However, designers must be cautious of the material's susceptibility to stress corrosion cracking (SCC) if exposed to chlorides while under high tensile stress. Furthermore, the fatigue limit in CH900 is optimized by the fine precipitate dispersion, making it superior to 302/304 stainless for high-cycle dynamic loading in flight control actuators.
