Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-05-26
2001-07-24
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S231000, C419S010000, C419S031000
Reexamination Certificate
active
06264718
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a powder metallurgy product and a method for producing the powder metallurgy product.
2. Description of the Background
In powder metallurgy, after some kinds of powders are mixed at a predetermined ratio, the mixed powder is formed into a desired shape under pressure and then sintered to be a final metallurgy product.
One of the advantages of powder metallurgy products is that machining operation is not necessary because powder metallurgy products having a substantially final shape may be formed in dies without machining operation. Recently, higher precision and more complex shapes have been required. Accordingly, machining operations have been required even for powder metallurgy products. However, generally, powder metallurgy products have poor machinability.
Japanese Examined Patent Publication (kokoku) 56-45964 (hereinafter referred to as the “'964 publication”) discloses steel powder having good machinability. The contents of this application are incorporated herein by reference in their entirety.
In the steel powder disclosed in the '964 publication, the steel powder contains S of 0.15 to 0.5 weight percent (wt %) and Mn of at most an amount greater than a Mn/S balance amount by 0.3 weight percent. Mn is used for combining with S. MnS is not easily oxidized after Mn combines with S.
Generally, powder metallurgy products have inferior mechanical strength. The reason is presumed that powder metallurgy products have many pores therein, because powder metallurgy products are produced by being formed under pressure and being sintered.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a powder metallurgy product which has improved machinability without substantially deteriorating fatigue strength.
According to one aspect of the invention, a powder metallurgy product is made from constituent including iron powder. The iron powder includes iron grains which contain machinability improving element in the iron grains. The machinability improving element is configured to improve machinability of the powder metallurgy product and has a pinning effect. An amount (Q) of the machinability improving element is adjusted such that an absolute value of a differential coefficient (dS/dQ) is at least a predetermined value, where (S) is a grain size of iron in the powder metallurgy product.
According to another aspect of the invention, a method for producing a powder metallurgy product includes adding machinability improving element to iron grains of iron powder so as to contain machinability improving element in the iron grains; forming the iron powder to a pre-product under pressure; and sintering the pre-product. The machinability improving element is configured to improve machinability of the powder metallurgy product and has a pinning effect. An amount (Q) of the machinability improving element is adjusted such that an absolute value of a differential coefficient (dS/dQ) is at least a predetermined value, where (S) is a grain size of iron in the powder metallurgy product.
REFERENCES:
patent: 5501728 (1996-03-01), Shepley et al.
patent: 5534220 (1996-07-01), Purnell et al.
patent: 5571305 (1996-11-01), Uenosono et al.
patent: 5631431 (1997-05-01), Andersson
patent: 5679909 (1997-10-01), Kaneko et al.
patent: 5938814 (1999-08-01), Uenosono et al.
Akagi Nobuaki
Kawai Shinya
Lutheran Michael E.
Satoh Masaaki
Suzuki Hironori
Kobelco Metal Powder of America, Inc.
Mai Ngoclan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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