Ferrous sintered alloy, process for producing ferrous sintered alloy and connecting rod

Abstract

A ferrous sintered alloy includes a sintered raw-material powder that is made of an Fe—Cr—Mo-system powder, a carbon-system powder and an Mn—Si-system powder before sintering. The ferrous sintered alloy exhibits a density of 7.4 g/cm 3 or more, and has a metallic structure that includes martensite and bainite. In the metallic structure, the martensite accounts for an area proportion of 40% or less when the entirety of the metallic structure is taken as 100% by area. Moreover, the martensite exhibits a particle diameter of 20 μm or less. The ferrous sintered alloy is good in terms of machinability.

1 . A ferrous sintered alloy being good in terms of machinability,
 the ferrous sintered alloy comprising a sintered raw-material powder being made of an Fe—Cr—Mo-system powder, a carbon-system powder and an Mn—Si-system powder before sintering;   the ferrous sintered alloy exhibiting a density of 7.4 g/cm 3  or more; and having a metallic structure comprising martensite and bainite; metallic structure in which the martensite accounts for an area proportion of 40% or less when the entirety of the metallic structure is taken as 100% by area and the martensite exhibits a particle diameter of 20 μm or less.   
     
     
         2 . The ferrous sintered alloy according to  claim 1 , wherein the raw-material powder comprises the carbon-system powder in an amount of from 0.3% bymass or more to 0.7% bymass or less, and the Mn—Si-system powder in an amount of from 0.4% by mass or more to 1% by mass or less when the entirety of the raw-material powder is taken as 100% by mass. 
     
     
         3 . The ferrous sintered alloy according to  claim 2 , wherein the raw-material powder comprises the carbon-system powder in an amount of from 0.5% by mass or more to 0.7% by mass or less when the entirety of the raw-material powder is taken as 100% by mass. 
     
     
         4 . The ferrous sintered alloy according to  claim 1 , wherein:
 the Fe—Cr—Mo-system powder comprises chromium (Cr) in an amount of from 0.5% by mass or more to 3.5% by mass or less, molybdenum (Mo) in an amount of from 0.1% by mass or more to 2% by mass or less, and the balance being Fe and inevitable impurities when the entirety of the Fe—Cr—Mo-system powder is taken as 100% by mass; and   the Mn—Si-system power is made of an Fe—Mn—Si-system powder comprising manganese (Mn) in an amount of from 40% by mass or more to 70% by mass or less, silicon (Si) in an amount of from 10% by mass or more to 40% by mass or less, and the balance being Fe and inevitable impurities when the entirety of the Fe—Mn—Si-systempowder is taken as 100% by mass.   
     
     
         5 . The ferrous sintered alloy according to  claim 1  comprising:
 chromium (Cr) in an amount of from 0.5% by mass or more to 3.5% by mass or less;   molybdenum (Mo) in an amount of from 0.1% by mass or more to 0.6% by mass or less;   silicon (Si) in an amount of from 0.04% by mass or more to 0.4% by mass or less;   manganese (Mn) in an amount of from 0.1% by mass or more to 0.7% by mass or less;   carbon (C) in an amount of from 0.3% by mass or more to 0.9% by mass or less; and   the balance being Fe and inevitable impurities;   when the entirety of the ferrous sintered alloy is taken as 100% by mass.   
     
     
         6 . The ferrous sintered alloy according to  claim 1  being made of at least one member that is selected from the group consisting of Cu-free ferrous sintered alloys, which are free from copper (Cu) substantially, and Ni-free ferrous sintered alloys, which are free from nickel (Ni) substantially. 
     
     
         7 . The ferrous sintered alloy according to  claim 1  exhibiting a Vickers hardness of from 300 Hv or more to 400 Hv or less; and a tensile strength of 960 MPa or more; at room temperature. 
     
     
         8 . The ferrous sintered alloy according to  claim 1  exhibiting the martensite proportion that falls in a range of from 4 to 40% with respect to the entire metallic structure being taken as 100% by area. 
     
     
         9 . The ferrous sintered alloy according to  claim 1 , wherein the martensite exhibits a particle diameter that falls in range of from 2 or more to 20 μm or less. 
     
     
         10 . The ferrous sintered alloy according to  claim 1  exhibiting the density that falls in a range of from 7.4 or more to 7.9 g/cm 3  or less. 
     
     
         11 . The ferrous sintered alloy according to  claim 7  exhibiting the tensile strength that falls in a range of from 960 or more to 1,500 MPa or less. 
     
     
         12 . The ferrous sintered alloy according to  claim 1 , wherein the Mn—Si-system powder comprises Mn and Si in a summed amount of from 75 to 85% by mass when the Mn—Si-system powder is taken as 100% by mass. 
     
     
         13 . The ferrous sintered alloy according to  claim 1 , wherein the Mn—Si-system powder exhibits a compositional ratio of Mn to Si falls in a range of from 0.5 to 4 by mass. 
     
     
         14 . The ferrous sintered alloy according  claim 5  comprising Cr in an amount of from 1.3 to 1.7% by mass when the entire ferrous sintered alloy is taken as 100% by mass. 
     
     
         15 . The ferrous sintered alloy according  claim 5  comprising Mo in an amount of from 0.1 to 0.3% by mass when the entire ferrous sintered alloy is taken as 100% by mass. 
     
     
         16 . A process for producing ferrous sintered alloy being good in terms of machinability, the ferrous sintered alloy having a metallic structure which comprises martensite and bainite, and in which the martensite accounts for an area proportion of 40% or less when the entirety of the metallic structure is taken as 100% by area and the martensite exhibits a particle diameter of 20 μm or less,
 the process comprising the steps of:   classifying an Mn—Si-system powder to particles that have a particle diameter of 5 μm or less at the maximum;   mixing an Fe—Cr—Mo-system powder, a carbon-system powder and the classified Mn—Si-system powder to prepare a raw-material powder;   compacting the resultant raw-material powder to turn it into a powder compact whose density is 7.4 g/cm 3  or more; and   sintering the powder compact to prepare a sintered body that has the metallic structure, the sintering step comprising the sub-steps of:
 heating the powder compact; and 
 cooling the heated powder compact to make the sintered body. 
   
     
     
         17 . The production process according to  claim 16 , wherein:
 the process is free from the compacting step, but comprises a step of compacting the raw-material powder as a simple powder compact; and   the sintering step comprises the sub-steps of :
 heating the resulting simple powder compact; 
 hot forging the heated simple powder compact to make a density of the simple powder compact 7.4 g/cm 3  or more; and 
 cooling the resultant hot-forged powder compact to make a sintered body that has the metallic structure. 
   
     
     
         18 . The production process according to  claim 16 , wherein the raw-material powder comprises the carbon-system powder in an amount of from0.3%bymass ormore to 0.7% bymass or less, andtheMn—Si-system powder in an amount of from 0.4% by mass or more to 1% by mass or less when the entirety of the raw-material powder is taken as 100% by mass. 
     
     
         19 . The production process according to  claim 18 , wherein the raw-material powder comprises the carbon-system powder in an amount of from 0.5% by mass or more to 0.7% by mass or less when the entirety of the raw-material powder is taken as 100% by mass. 
     
     
         20 . The production process according to  claim 16 , wherein:
 the Fe—Cr—Mo-system powder comprises chromium (Cr) in an amount of from 0.5% by mass or more to 3.5% by mass or less, molybdenum (Mo) in an amount of from 0.1% by mass or more to 2% by mass or less, and the balance being Fe and inevitable impurities when the entirety of the Fe—Cr—Mo-system powder is taken as 100% by mass; and   the Mn—Si-system power is made of an Fe—Mn—Si-system powder comprising manganese (Mn) in an amount of from 40% by mass or more to 70% by mass or less, silicon (Si) in an amount of from 10% by mass or more to 40% by mass or less, and the balance being Fe and inevitable impurities when the entirety of the Fe—Mn—Si-system powder is taken as 100% by mass.   
     
     
         21 . The production process according to  claim 16 , wherein the powder compact is heated at a temperature of from 1,100 to 1,370° C. for a time period of from 1 to 60 minutes in the heating sub-step of the sintering step. 
     
     
         22 . The production process according to  claim 16 , wherein the heated powder compact is cooled at a cooling rate of from 30° C./minute or more to 100° C./minute or less in the cooling sub-step of the sintering step. 
     
     
         23 . The production process according to  claim 16 , wherein not only the Mn—Si-system powder but also the Fe—Cr—Mo-system powder are classified in the classifying step. 
     
     
         24 . The production process according to  claim 17 , wherein a lubricant agent is further added to the raw-material powder in the raw-material-powder mixing step. 
     
     
         25 . A connecting rod comprising the ferrous sintered alloy according to  claim 1 . 
     
     
         26 . A connecting rod being manufactured by means of the production process according to  claim 16 .