Machine part and process for producing same

Abstract

Provided is a gear ( 1 ) (machine part), including a sintered compact obtained by sintering a green compact of raw material powder ( 10 ) that contains as a main raw material iron-based alloy powder containing molybdenum and has 0.1 to 0.8 mass % of carbon powder blended therein, the gear ( 1 ) (machine part) including a hardened layer ( 8 ) formed through heat treatment after the sintering, and having a true density ratio of 97% or more and less than 100%.

1 . A machine part, comprising a sintered compact obtained by sintering a green compact of raw material powder that contains as a main raw material iron-based alloy powder containing molybdenum and has 0.1 to 0.8 mass % of carbon powder blended therein,
 the machine part including a hardened layer formed through heat treatment after the sintering, and having a true density ratio of 97% or more and less than 100%.   
     
     
         2 . The machine part according to  claim 1 , wherein at least a part of the hardened layer comprises a dense layer in which a porous structure is more densified than in another area. 
     
     
         3 . The machine part according to  claim 1 , wherein a hardness of the machine part gradually reduces from a surface to a core portion. 
     
     
         4 . The machine part according to  claim 1 , wherein the iron-based alloy powder contains 0.2 to 0.8 mass % of molybdenum, given that a mass of the raw material powder is defined as 100. 
     
     
         5 . The machine part according to  claim 1 , wherein the iron-based alloy powder further contains 0.2 to 0.8 mass % of nickel, given that a mass of the raw material powder is defined as 100. 
     
     
         6 . A method of manufacturing a machine part comprising a sintered compact having a true density ratio of 97% or more and less than 100%, the method comprising:
 a compression molding step of compression molding raw material powder that contains as a main raw material iron-based alloy powder containing molybdenum and has 0.1 to 0.8 mass % of carbon powder blended therein, in a mold to obtain a green compact;   a sintering step of heating the green compact at a temperature equal to or higher than a sintering temperature of the iron-based alloy powder to obtain a sintered compact; and   a heat treatment step of subjecting the sintered compact to heat treatment to form a hardened layer.   
     
     
         7 . The method of manufacturing a machine part according to  claim 6 , wherein the compression molding step comprises compression molding the raw material powder in a state in which a solid lubricant adheres to a molding surface of the mold. 
     
     
         8 . The method of manufacturing a machine part according to  claim 6 , wherein the raw material powder to be used has a solid lubricant added thereto. 
     
     
         9 . The method of manufacturing a machine part according to  claim 7 , wherein the compression molding of the raw material powder is performed in a state in which the mold is heated. 
     
     
         10 . The method of manufacturing a machine part according to  claim 6 , further comprising a plastic processing step of subjecting the sintered compact to plastic processing between the sintering step and the heat treatment step. 
     
     
         11 . The method of manufacturing a machine part according to  claim 10 , wherein the plastic processing comprises rolling processing. 
     
     
         12 . The method of manufacturing a machine part according to  claim 8 , wherein the compression molding of the raw material powder is performed in a state in which the mold is heated.