| 摘要 |
PROBLEM TO BE SOLVED: To continuously hold rust preventing effect in the powder and to maintain the rust preventing effect also by sintering by mixing a powdery mixture contg. copper powder with Bi powder so as to control the content of Bi to a specified ratio. SOLUTION: A powdery mixture for powder metallurgy contg. copper powder is mixed with Bi powder so as to control the content of Bi to 20 to 400 ppm (wt), preferably to 30 to 300 ppm (wt). Moreover, the powdery mixture for powder metallurgy is the one essentially consisting of copper powder, the raw material such as graphite may be added thereto, the copper powder is the one contg. about >=50 wt.% Cu, and the Bi powder is the one contg. about >=1% Bi. When, using the mixed raw material obtd. in this way, a green compact having a prescribed shape is formed, which is sintered at about 700 to 800 deg.C, the surface of the sintered body is coated with a thin Bi layer, and the sintered body having effective rust preventing effect by the presence of a trace amt. of Bi can be obtd. Moreover, the content of Bi in the surface layer part in the range of 1μm from the topmost surface in the sintered body is made higher than the Bi content in the remaining part by >=10 times.
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