Method of producing wear-resistant iron-based sintered alloy

Abstract

A wear-resistant iron-based sintered alloy made of a mixed powder including first hard particles, second hard particles, graphite particles, and iron particles is produced. The first hard particles are Fe—Mo—Ni—Co—Mn—Si—C alloy particles. The second hard particles are Fe—Mo—Si alloy particles. The mixed powder includes the first hard particles at 5 mass % to 50 mass %, the second hard particles at 1 mass % to 8 mass %, and the graphite particles at 0.5 mass % to 1.5 mass % when a total amount of the above particles is set as 100 mass %. In a sintering process, sintering is performed so that the hardness of the first hard particles becomes 400 to 600 Hv and the hardness of the second hard particles exceeds 600 Hv. Then, an oxidation treatment is performed so that a density difference between before and after the oxidation treatment in a sintered product becomes 0.05 g/cm 3 or more.

What is claimed is: 
     
         1 . A method of producing a wear-resistant iron-based sintered alloy comprising:
 a molding process in which a mixed powder including hard particles, graphite particles, and iron particles is compact-molded into a molded product for a sintered alloy; and   a sintering process in which the molded product for the sintered alloy is sintered while C of the graphite particles of the molded product for the sintered alloy diffuses into the hard particles and the iron particles,   wherein the hard particles include first hard particles and second hard particles,   wherein the first hard particles include Mo: 20 mass % to 70 mass %, Ni: 5 mass % to 40 mass %, Co: 5 mass % to 40 mass %, Mn: 1 mass % to 20 mass %, Si: 0.5 mass % to 4.0 mass %, and C: 0.5 mass % to 3.0 mass %, with the balance including Fe and inevitable impurities when an amount of the first hard particles is set as 100 mass %,   wherein the second hard particles include Mo: 60 mass % to 70 mass %, and Si: 2.0 mass % or less, with the balance including Fe and inevitable impurities when an amount of the second hard particles is set as 100 mass %,   wherein the mixed powder includes the first hard particles at 5 mass % to 50 mass %, the second hard particles at 1 mass % to 5 mass %, and the graphite particles at 0.5 mass % to 1.5 mass % when a total amount of the first hard particles, the second hard particles, the graphite particles, and the iron particles is set as 100 mass %, and   wherein, in the sintering process, sintering is performed so that the hardness of the first hard particles becomes 400 to 600 Hv and the hardness of the second hard particles exceeds 600 Hv, after the sintering process, an oxidation treatment is performed on a sintered product sintered from the molded product for the sintered alloy so that a part of iron contained in an iron matrix derived from the iron particles becomes triiron tetraoxide, and the oxidation treatment is performed so that a difference between a density of the sintered product before the oxidation treatment and a density of the sintered product after the oxidation treatment becomes 0.05 g/cm 3  or more.   
     
     
         2 . The method according to  claim 1 , wherein 10 mass % or less of Cr is additionally added to the first hard particles when the amount of the first hard particles is set as 100 mass %. 
     
     
         3 . The method according to  claim 1 , wherein a particle size of the second hard particles is in a range of 100 μm or less.