Answer
17-7PH is used in two primary heat-treated conditions for spiral rings. Condition CH900 involves cold-rolling the material to a high strength (Condition C) followed by age hardening. This results in the highest possible tensile strength ($240 ksi$) but lower ductility. RH950 involves a solution treatment, followed by a sub-zero transformation to martensite and then aging at $950^\circ F$. RH950 provides better dimensional stability and higher toughness, though slightly lower strength than CH900. For most spiral ring applications, CH900 is the standard because the coiling process benefits from the high initial strength of the cold-rolled wire. However, for large-diameter rings where installation requires significant expansion without snapping, the increased toughness of RH950 may be preferred to prevent brittle fracture.
