Producing metal member with enhanced corrosion resistance by salt bath nitriding

• Main Authors: YASHIRO, KUNIJI, YAMAMURA, TETSUYA, EIRAKU, HIROSHI, NAKAMURA, FUMIHIDE, TENMAYA, MOTOHIRO, SAWANO, YUTAKA
• Format: Patent
• Language: English; French; German
• Published: 03.10.2007
• Subjects: APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TO SURFACES, IN GENERAL; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; METALLURGY; PERFORMING OPERATIONS; PROCESSES FOR APPLYING LIQUIDS OR OTHER FLUENT MATERIALS TOSURFACES, IN GENERAL; SPRAYING OR ATOMISING IN GENERAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; TRANSPORTING

A metal member is produced with enhanced corrosion resistance by salt bath nitriding. Specifically, in a nitriding salt bath containing Li<+>, Na<+> and K<+> ions as cation components and CNO<-> and CO3<--> ions as anion components and enhanced in oxidizing power by addition of an oxidizing-power-enhancing substance selected from the group consisting of alkali metal hydroxides, bound water, free water and moist air, the metal member is immersed such that an nitrided layer is formed on a surface of the metal member and concurrently, an oxide film is formed on an outermost layer of the nitrided layer. As a subsequent step to the immersion in the nitriding salt bath, the metal member is immersed in a displacement cleansing salt bath which contains an alkali metal nitrate.