Iron base sintered alloy and method for manufacturing the same

Abstract

An iron base sintered alloy has a chemical composition including at least Fe, Cu and C, and a sintered structure including a residual austenite and a martensite. The sintered structure includes a precipitated Cu element that was dissolved in the martensite and that has been precipitated from the martensite. A method for manufacturing an iron base sintered alloy includes conducting a Cu precipitation treatment for a sintered alloy that has a chemical composition including at least Fe, Cu and C, and a sintered structure including a residual austenite and a martensite to precipitate Cu element dissolved in the martensite.

What is claimed is: 
     
         1 . An iron base sintered alloy comprising:
 a chemical composition including at least Fe, Cu and C; and   a sintered structure including a residual austenite and a martensite, wherein   the sintered structure includes a precipitated Cu element that was dissolved in the martensite and that has been precipitated from the martensite.   
     
     
         2 . The iron base sintered alloy according to  claim 1 , wherein
 the precipitated Cu element includes intermetallic compound of Cu.   
     
     
         3 . The iron base sintered alloy according to  claim 2 , wherein
 the intermetallic compound of Cu includes Fe—Cu intermetallic compound.   
     
     
         4 . The iron base sintered alloy according to  claim 3 , wherein
 the sintered structure shows a peak of the Fe—Cu intermetallic compound at an energy absorption edge of K-cell of Cu in X-ray absorption fine structure analysis, and   an area intensity of the peak of the Fe—Cu intermetallic compound is equal to or greater than 0.125.   
     
     
         5 . The iron base sintered alloy according to  claim 1 , wherein
 the sintered structure shows a peak of Fe—Cu solid solution at an energy absorption edge of K-cell of Cu in X-ray absorption fine structure analysis, and   an area intensity of the peak of the Fe—Cu solid solution is equal to or less than 1.620.   
     
     
         6 . The iron base sintered alloy according to  claim 1 , wherein
 a content of Cu in the martensite measured by energy dispersive X-ray analysis with a transmission electron microscope is less than 0.5% by mass.   
     
     
         7 . The iron base sintered alloy according to  claim 1 , wherein
 the iron base sintered alloy is to be included in a member for an engine of an automobile.   
     
     
         8 . A method for manufacturing an iron base sintered alloy, the method comprising:
 conducting a Cu precipitation treatment for a sintered alloy that has a chemical composition including at least Fe, Cu and C, and a sintered structure including a residual austenite and a martensite to precipitate Cu element dissolved in the martensite.   
     
     
         9 . The method for manufacturing the iron base sintered alloy according to  claim 8 , wherein
 the Cu precipitation treatment includes a thermal treatment applying a thermal energy, and   the thermal energy is equivalent to a thermal energy that is calculated from a temperature in which a sintered member made of the iron base sintered alloy is to be used and a life of the sintered member.   
     
     
         10 . The method for manufacturing the iron base sintered alloy according to  claim 8 , wherein
 the Cu precipitation treatment is conducted so that a content of Cu in the martensite measured by energy dispersive X-ray analysis with a transmission electron microscope is less than 0.5% by mass in the sintered structure after the Cu precipitation treatment.   
     
     
         11 . An iron base sintered alloy having a chemical composition including at least Fe, Cu and C, the iron base sintered alloy comprising:
 a sintered structure including a residual austenite, a martensite and a precipitated Cu element precipitated from the martensite.