PH13-8 Mo Stainless Steel (UNS S13800) is a martensitic precipitation-hardening stainless steel that has excellent strength, high hardness, superior toughness, and good corrosion resistance. Good transverse toughness properties are achieved by tight chemical composition control, low carbon content, and vacuum melting. The alloy is produced by vacuum induction melting (VIM) followed by electro-slag remelting (ESR). As a result of this melt practice, excellent macro- and microcleanliness is achieved, and tight compositional control is implemented.

The strengthening mechanism (precipitation hardening in a martensitic matrix) makes it possible to achieve uniform strengthening in heavy sections. Strength and ductility levels can be tailored to the application by varying the aging temperature.

PH13-8Mo is martensitic in structure in the solution annealed condition and is further strengthened by a relatively low temperature heat treatment, which precipitates a strengthening phase in the alloy. Compared to 17-4PH, PH13-8Mo requires only a simple heat treatment, a one step process conducted at a temperature in the range 950°F (510°C) to 1150°F (620°C) depending on the combination of strength and toughness desired.