Iron based sintered body excellent in enveloped casting property in light metal alloy and method for producing the same

Abstract

An iron based sintered body suitable for being enveloped in a light metal alloy such as an aluminum alloy by casting, and a method for producing the same. A mixed powder is prepared by mixing an iron based powder, a copper powder and a graphite powder blended so that the Cu content and the C content are 5 to 40% by mass and 0.5 to 2.5% by mass, respectively, in the mixed powder. A lubricant powder and a fine particle powder for improving machinability may be further added in the mixed powder. Then, the mixed powder is filled into a mold formed to a green compact, and is sintered into a sintered body so that the sintered body has a desired average thermal expansion coefficient. The surface of the sintered body may be adjusted to have a surface roughness Rz of 10 to 100 μm optionally by applying a shot blast treatment or by a shot blast treatment and an additional steam treatment. This process permits the sintered body to be enhanced in adhesive property and bonding strength while being improved in enveloping casting property when the sintered body is enveloped in the light metal alloy by casting. A martesitic stainless steel powder or ferritic stainless steel powder may be used instead of the pure iron powder, or Cr, Mo and W powders may be further blended.

1 . A method for producing an iron based sintered body used for being enveloped in a light metal alloy by casting comprising the steps of: 
 preparing a mixed powder by blending an iron based powder, a copper powder, a graphite powder and a lubricant powder;    filling the mixed powder into a mold;    forming a green compact by press-molding; and    forming a sintered body by sintering the green compact; wherein    a pure iron is used as the iron based powder,    the copper powder and the graphite powder are blended so that the Cu content is 5 to 40% by mass and the C content is 0.5 to 2.5% by mass relative to the total amount of the iron based powder, the copper powder and graphite powder in the mixed powder,    at least any one of the molding condition of the compressed powder and sintering condition of the sintering is controlled so that the average thermal expansion coefficient of the sintered body is 13.5×10 −6 /° C. or less from room temperature to 200° C.; and    the surface roughness Rz is adjusted to 10 to 100 μm.    
   
   
       2 . The method for producing the iron based sintered body according to  claim 1 , wherein any one of a ferritic stainless steel powder, a martensitic stainless steel powder, pure iron powder and ferritic stainless steel powder, pure iron powder and martensitic stainless steel powder, is used as the iron based powder, instead of the pure iron powder for the iron based powder.  
   
   
       3 . The method for producing the iron based sintered body according to  claim 1 , further comprising applying a steam treatment after the shot blast treatment.  
   
   
       4 . The method for producing the iron based sintered body according to  claim 1 , wherein the mixed powder contains, relative to the total amount of the mixed powder, 0.1 to 5% by mass of the fine particle powder for improving machinability comprising at least one element selected from the group consisting of MnS powder, CaF 2  powder, BN powder and enstatite powder with a particle diameter of 150 μm or less.  
   
   
       5 . The method for producing the iron based sintered body according  claim 1 , wherein the mixed powder is further with blended any one of a Cr powder, Mo powder, W powder, Fe—Cr powder, Fe—Mo powder and Fe—W powder, alone or in combination, as an alloy element powder, 
 so that the mixed powder comprises, in % by mass, 40% or less in total of at least one element selected from the group consisting of 30% or less of Cr, 10% or less of Mo, 5% or less of W, 3% or less of Si and 2.5% or less of Mn relative to the total amount of the mixed powder.    
   
   
       6 . The method for producing the iron based sintered body according to  claim 1 , wherein a groove is formed further on any one of end faces and side faces or both, of the green compact in the press-molding step.  
   
   
       7 . The method for producing the iron based sintered body according to  claim 1 , wherein a groove is formed further on any one of end faces and side faces or both, of the green compact in the press-molding and a succeeding machining step.  
   
   
       8 . The method for producing the iron based sintered body according to  claim 1 , wherein a groove is formed further on any one of end faces and side faces or both, of the sintered body by machining after sintering.  
   
   
       9 . The method for producing the iron based sintered body according to  claim 1 , wherein the surface roughness Rz is adjusted by applying a shot blast treatment to the sintered body.