Abstract: Duplex coated steel composite products comprising a first layer of a nitrd layer formed by applying glow discharge at a current density from 0.001 to 2.0 mA/cm.sup.2 to the surface of metal parts by using gaseous ammonia and gaseous hydrogen while maintaining the temperature of the metal parts at 300 to 650.degree. C., thereby applying plasma nitriding and a second layer comprising a hard film comprising a nitride, carbide and/or carbonitride of one or more of elements selected from Ti, Zr, Hf, V, Nb, Ta and Cr coated on the first layer by the PVD method of a laminate film or a gradient laminate film of such hard film. The treated products are excellent in adhesion with the substrate and durability and have both oxidation resistance and wear resistance.

Abstract: Duplex coated steel composite products comprising a first layer of a nitrided layer formed by applying glow discharge at a current density from 0.001 to 2.0 mA/cm.sup.2 to the surface of metal parts by using gaseous ammonia and gaseous hydrogen while maintaining the temperature of the metal parts at 300 to 650.degree. C., thereby applying plasma nitriding and a second layer comprising a hard film comprising a nitride, carbide and/or carbonitride of one or more of elements selected from Ti, Zr, Hf, V, Nb, Ta and Cr coated on the first layer by the PVD method of a laminate film or a gradient laminate film of such hard film. The treated products are excellent in adhesion with the substrate and durability and have both oxidation resistance and wear resistance.