Metal powder for powder metallurgy, compound, granulated powder, sintered body, and method for producing sintered body

Abstract

A metal powder for powder metallurgy includes particles each having a first region containing Fe as a principal component, a second region, in which the content of a first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and a third region, in which the content of a second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region. Further, the first region occupies 50% by volume or more of each of the particles and also is crystalline.

What is claimed is: 
     
         1 . A metal powder for powder metallurgy, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder comprises particles each having:
 a first region containing Fe as a principal component;   a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and   a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and   the first region occupies 50% by volume or more of each of the particles and also is crystalline.   
     
     
         2 . The metal powder for powder metallurgy according to  claim 1 , wherein the content of O in each of the second region and the third region is higher than in the first region. 
     
     
         3 . The metal powder for powder metallurgy according to  claim 1 , wherein the second region and the third region are present in the first region and are disposed apart from each other. 
     
     
         4 . The metal powder for powder metallurgy according to  claim 1 , wherein
 in the cross section of each of the particles, the second region and the third region each have a particle form, and   the particle diameter of each of the second region and the third region is 0.01% or more and 0.9% or less of the particle diameter of the particle.   
     
     
         5 . The metal powder for powder metallurgy according to  claim 1 , wherein in each of the particles, the first region is formed from a single crystal. 
     
     
         6 . The metal powder for powder metallurgy according to  claim 5 , wherein in the metal powder for powder metallurgy, the particles are contained in an amount of 50% by number or more. 
     
     
         7 . The metal powder for powder metallurgy according to  claim 1 , wherein each of the particles contains:
 Fe as a principal component;   Cr in a proportion of 10% by mass or more and 30% by mass or less;   Si in a proportion of 0.3% by mass or more and 1.2% by mass or less;   C in a proportion of 0.005% by mass or more and 1.2% by mass or less;   the first element in a proportion of 0.01% by mass or more and 0.5% by mass or less; and   the second element in a proportion of 0.01% by mass or more and 0.5% by mass or less.   
     
     
         8 . A compound, comprising the metal powder for powder metallurgy according to  claim 1  and a binder which binds the particles of the metal powder for powder metallurgy to one another. 
     
     
         9 . A granulated powder, wherein the granulated powder is obtained by granulating the metal powder for powder metallurgy according to  claim 1 . 
     
     
         10 . A sintered body, wherein when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the sintered body comprises:
 a first region containing Fe as a principal component;   a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region; and   a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region.   
     
     
         11 . The sintered body according to  claim 10 , wherein the content of O in each of the second region and the third region is higher than in the first region. 
     
     
         12 . The sintered body according to  claim 10 , wherein in the cross section of the sintered body, the second region and the third region each have a particle form with a particle diameter of 10 nm or more and 1000 nm or less. 
     
     
         13 . A method for producing a sintered body, comprising:
 molding a composition containing a metal powder for powder metallurgy, thereby obtaining a molded body; and   firing the molded body, thereby obtaining a sintered body, wherein   when one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a first element, and one element selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in the periodic table than that of the first element or having the same group number in the periodic table as that of the first element and a larger period number in the periodic table than that of the first element is defined as a second element, the metal powder for powder metallurgy includes particles each having   a first region containing Fe as a principal component,   a second region, in which the content of the first element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and   a third region, in which the content of the second element is higher than in the first region, the content of Si is higher than in the first region, and the content of Fe is lower than in the first region, and   the first region occupies 50% by volume or more of each of the particles and also is crystalline.