PURPOSE: To form a tough diffused coating on the surface of a metal such as Fe etc., by applying a mixt. of a halide, an org. resin, and a Cr-Al alloy power on the metal surface, then by heating the metal in an inert atmosphere.

CONSTITUTION: On the surface of a metallic member made of Fe, Ni, Co or an alloy of these metals i applied a mixt. of the following composition: A mixt. comprising 0.5W10% by wt. one or more members selected from the group consisting of halides of ammonium, Cr, Al; 5W30% org. resin such as acryl resin, polyvinyl alcohol; 15W60% Al; the balance being Al-Cr alloy powder. The metal member applied with the mixt. is heated to a temp. 900W1,150°C in an inert atmosphere such as Ar gas, a reducing atmosphere such as hydrogen gas, or in vacuum. Hereby, the applied mixt. is diffused into the metal, forming very tough diffused coating.