Stainless steels are iron based alloys containing at least 10.5% Chromium. They achieve their stainless characteristics through the formation of an invisible and adherent Chromium rich oxide film. 15-7PH is an alloy which can be precipitation hardened by heat treatment to form a martensitic phase.Foil - Thin sheets of pure metal and metal alloys. Due to their fragile nature, some foils are coated on one side with an acrylic or polyester support. Where foils are supported they are indicated in the detailed item description.