PURPOSE: To obtain machine parts made of a precipitation hardening alloy with corrosion resistance and high strength, by forming a worked layer on the surface of a precipitation hardening alloy in a solubilized state and by subjecting the alloy to age heat treatment.

CONSTITUTION: A precipitation hardening material such as an Ni or Cr alloy is forged or mechanically worked and subjected to soln. heat treatment. A worked layer having ≥ about 50μm thickness is formed on the surface of the material by peening or other method, and the material is subjected to age heat treatment. By this method a layer with superior mechanical strength remains on the surface, superior mechanical strength is provided as a whole, and machine parts with improved corrosion resistance and stress corrosion cracking resistance are obtd.