Precipitation Hardening (PH) stainless steels are classified as martensitic or semi-austenitic. They develop their high strength and hardness through a variety of heat treatments resulting in a very high strength-to-weight ratio. Semi-austenitic grades are 17-7 PH® and PH 15-7 Mo®. They are austenitic in the annealed state, and martensitic in the hardened condition. Martensitic grades include 17-4 PH® and 15-5 PH®. The PH grades achieve high tensile properties in heat treated conditions. Applications for PH steels include aerospace components, flat springs, and retaining rings.