AMS 5659 is an aerospace material specification for a premium quality corrosion resistant
precipitation hardenable steel alloy. Common names for the alloy are 15-5 or UNS S15500.
AMS 5659 includes material in the form of bars, wire,forgings, forging stock, tubing, and rings.
This alloy is typically used where a combination of strength and corrosion resistance is required
in applications with service temperatures up to 600 deg F.
AMS 5659 requires consumable electrode remelting to premium aircraft quality standards
With the exception of forging stock, material to this standard is supplied in the solution heat
treated condition that can be readily heat treated to final properties during the manufacture of
component parts.
To assure the results of the final precipitation hardening treatment; samples of the product are
precipitation hardened to the H900 condition and tensile tested for conformance to specification
minimum requirements.

For more info on stainless steel grade 15-5 check out the long video here, for more info about the metal you can also check out the grade page here.