15-5PH Stainless Steel (AMS 5659, EN 1.4545, X5CrNiCuNb15-5)

15-5 PH stainless steel, which belongs to the precipitation hardening (PH) martensitic stainless steel group, is an engineering material that stands out for its high strength, excellent corrosion resistance, and superior toughness. The UNS number for 15-5 PH steel, defined according to the ASTM A564 standard, is S15500, and its equivalent in European standards is EN 1.4545 (X5CrNiCuNb15-5).

Widely preferred in the aerospace and defense industries, this steel is used in accordance with aerospace standards such as AMS 5659 primarily, as well as AMS 5862, AMS 5867, and AMS 5663. Thanks to different heat treatment conditions such as H900, H1025, and H1075, the strength–toughness balance of 15-5 PH can be tailored to specific applications. Compared to 17-4 PH (1.4548) steel, 15-5 PH offers a more homogeneous microstructure and lower anisotropy. In applications requiring high reliability—such as aircraft components, precision mechanical parts, molds, and fasteners—15-5 PH stainless steel is a preferred material due to its long service life and dimensional stability.

According to the AMS 5659 standard, 15-5 PH stainless steel is classified into two types based on the melting practice. Type 1 refers to steels produced by VAR (Vacuum Arc Remelting) or the CEVM process, while Type 2 covers materials remelted by the ESR (Electroslag Remelting) method. This classification affects the homogeneity of the microstructure, gas and inclusion content, and ultimately the mechanical performance of the steel.