Method for Activating Surface of Metal Member

Abstract

A passivated film on a surface of a high-alloy steel member makes it difficult to apply diffusion treatment, such as gas nitriding or gas carburizing, that forms a nitrided layer, carburized layer or carbonitrided layer on the surface of the steel member. An activating treatment method is provided for the surface of the metal member. This method is not accompanied by problems of conventional activation treatment with a halide, such as furnace deposits, furnace wall erosion and effluent gas detoxification treatment, and is useful as pretreatment for diffusion treatment. According to this method, the passivated surface of the high-alloy steel member can be activated by using a gas commonly employed in gas heat treatment, and forming HCN gas in a heating furnace while making use of catalytic action of the steel member or a surface of the furnace.

1 . A method for activating a surface of a metal member, which comprises heating a mixed gas of a carbon donor compound, which is gaseous at normal temperature and pressure, and ammonia as essential components to at least 300° C. in a heating furnace to form HCN under catalytic action of said metal member, a metal-made inner wall of said furnace or a metal-made jig in the thus-heated mixed gas, and causing the thus-formed HCN to act on said surface of said metal member.  
   
   
       2 . A method according to  claim 1 , wherein said carbon donor compound is at least one compound selected from acetylene, ethylene, propane, butane and carbon monoxide.  
   
   
       3 . A method according to  claim 1 , wherein said metal-made inner wall of said heating furnace or said metal-made jig contains at least one metal selected from Fe, Ni, Co, Cu, Cr, Mo, Nb, V, Ti and Zr.  
   
   
       4 . A method according to  claim 1 , wherein HCN is formed to at least 100 mg/m 3  in said heating furnace and a furnace atmosphere gas has a dew point not higher than 5° C.