15-5 stainless steel is a martensitic, precipitation-hardening material with chromium, nickel and copper.  It is often a first choice in the aerospace industry for fasteners and structural components.  Its unique structure provides increased toughness and better corrosion resistance than its predecessor, 17-4 PH.  Both inclusion control and a minimized amount of delta ferrite as compared to 17-4 stainless steel contribute to the greater toughness of 15-5.  The alloy is further strengthened by a low temperature heat treatment which precipitates a copper containing phase in the alloy.  15-5 PH is able to meet the stringent mechanical properties required in the aerospace and nuclear industries.

17-4 PH is a martensitic, chromium-nickel-copper precipitation-hardening stainless steel. 17-4 PH stainless steel is capable of attaining a wide range of strength and toughness properties depending on the precipitation or aging temperature used in hardening.  Its valuable combination of  high strength, good corrosion resistance and toughness in both base metals and welds gives designers opportunities to add reliability to their products while simplifying fabrication and often reducing costs. High strength is maintained to approximately 600°F (316°C). This material has good resistance to stress corrosion cracking in the lower strength conditions.