Nitriding Treatment Method and Nitriding Treatment Apparatus

Abstract

The present invention provides a nitriding treatment method for forming a compound layer of ε phase (Fe2-3N) and γ′ phase (Fe4N) iron nitride excellent in wear durability in a steel material, from which a sliding member is formed, by short treatment, with a high thermal efficiency, with a reduced amount of used nitriding gas, and with a low environmental load. The nitriding treatment method of the present invention includes heating a sliding member made of a steel material at a temperature of 600° C. to 700° C. for a time of 1 to 25 minutes under an atmosphere of nitriding gas through high frequency induction heating or resistive heating, to form a compound layer of ε phase (Fe2-3N) and γ′ phase (Fe4N) iron nitride, the compound layer having a nitrogen content of higher than 4.5%, in a surface layer portion of the sliding member.

1 . A nitriding treatment method comprising:
 heating a sliding member made of a steel material at a temperature of 600° C. to 700° C. for a time of 1 to 25 minutes under an atmosphere of nitriding gas through high frequency induction heating or resistive heating, to form a compound layer of ε phase (Fe 2-3 N) and γ′ phase (Fe 4 N) iron nitride, the compound layer having a nitrogen content of higher than 4.5%, in a surface layer portion of the sliding member.   
     
     
         2 . The nitriding treatment method according to  claim 1 , wherein,
 after the sliding member is heated, the sliding member is cooled.   
     
     
         3 . The nitriding treatment method according to  claim 1 , wherein
 the nitriding gas is supplied to a surface of the sliding member via natural convection or forced convection.   
     
     
         4 . A nitriding treatment apparatus comprising:
 a nitriding chamber in which a sliding member made of a steel material is to be placed;   a high frequency heating coil disposed in the nitriding chamber to subject the sliding member to high frequency heating;   a vacuum pump that evacuates the nitriding chamber;   a nitriding gas cylinder that supplies nitriding gas to the nitriding chamber;   a nitrogen gas cylinder that supplies nitrogen gas to the nitriding chamber;   a high frequency power source connected to the high frequency heating coil to energize the high frequency heating coil; and   a forced convection generating unit disposed in the nitriding chamber to generate forced convection in the nitriding gas.   
     
     
         5 . The nitriding treatment apparatus according to  claim 4 , wherein
 the forced convection generating unit is a stirrer that stirs the nitriding gas.   
     
     
         6 . The nitriding treatment apparatus according to  claim 4 , wherein
 the forced convection generating unit is an up-down drive unit that moves the sliding member up and down.   
     
     
         7 . The nitriding treatment apparatus according to  claim 4 , wherein
 the forced convection generating unit is a rotary drive unit that rotates the sliding member.