NITRIDING METHOD OF FERROUS ALLOY BASE MATERIAL

• Main Authors: BABA TADAO, KOSUGI MASAKI, AKAISHIZAWA MASAHIRO
• Format: Patent
• Language: English
• Published: 17.08.2006
• Subjects: 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; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION

PROBLEM TO BE SOLVED: To provide a nitriding method of a ferrous alloy base material capable of realizing the substantially uniform thickness of a nitrided layer, and avoiding brittleness of the nitrided ferrous alloy base material. SOLUTION: After an engine valve 10 is accommodated in a treatment furnace, the temperature is raised while performing evacuation, and when the temperature becomes higher than 400°C, preferably, ≥450°C, supply of gaseous hydrogen is started to start the gaseous hydrogen sputtering (a first step). A passive film present on a surface of the engine valve 10 is reduction-removed. Evacuation and temperature raise are continued while performing the gaseous hydrogen sputtering, and preferably, when the temperature reaches 500°C, gaseous nitrogen is introduced together with gaseous hydrogen to start a second step. By this gaseous nitrogen the surface of the engine valve 10 with the passive film removed therefrom is nitrided to form a nitrided layer. COPYRIGHT: (C)2006,JPO&NCIPI