A method and apparatus for manufacturing a part. The part may be positioned in a chamber. The part may be comprised of a metal and may be a positioned part. A gas containing nitrogen may be sent into the chamber. An electromagnetic field may be generated in the chamber with the gas. The electromagnetic field may heat a portion of the metal in the positioned part to a temperature from about 60 percent to about 99 percent of the melting point of the metal such that the portion of the metal has a desired hardness. The portion of the metal may extend from a surface of the positioned part to a selected depth from the surface.