Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
2000-08-16
2001-10-02
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S252000
Reexamination Certificate
active
06296682
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an iron based blended powder for powder metallurgy. It is more particularly concerned with an iron based blended powder for powder metallurgy which, after having been sintered, provides a reformable sintered article having a good sliding property, less variation in this property, and a good impact resistance.
BACKGROUND ART
The iron based blended powder for powder metallurgy is formed by blending an iron powder with a Cu powder or carbon powder, compacted in a die, and then sintered into a sintered body having ordinarily a density of 5.0 to 7.2 g/cm
3
to be used as mechanical parts and so forth. In order to improve the sliding property of a sintered article that is to be used as mechanical parts or the like, such sintered steel as contains free graphite like cast iron is considered effective.
For example, Japanese Patent Laid-Open Publication No. Hei 8-209202 has suggested such a blended powder that provides a sintered article which contains a maximum of 0.5% by weight of free graphite therein and has an improved sliding property. The blended powder is formed by blending an iron power with a graphite powder, the iron powder containing B, Cr, and Mn, as well as one or more elements selected from the group consisting of S, Se, and Te, and a partially alloyed element selected from the group consisting of Ni, Cu, and Mo.
Furthermore, Japanese Patent Laid-Open Publication No. Hei 8-144,026 discloses a structure, of a free graphite precipitate iron based sintered article with high strength and a high toughness, containing C, Ni, Mo, Cu, BN, and S with the residue Fe and unavoidable impurities, said BN being distributed in the boundary faces of said polycrystalline bodies.
However, recently, various types of drive units for use in automobiles or the like have increasingly been required to provide higher output and reduced weight, leading to more extreme conditions for the sliding parts to be used therein, so that sintered articles are required to have still further improved sliding properties.
However, in order to increase the content of free carbon in a sintered article to 0.5% by weight or more, merely increasing the quantity of carbon to be blended into an iron based blended powder for powder metallurgy as set forth in Japanese Patent Laid-Open Publication No. Hei 8-209202 would cause the sintered article to increase in brittleness due to excessive carbonization, thus raising such problems that the impact resistance is reduced and the sintered article cannot be reformed. Furthermore, merely increasing the content of the carbon added to said iron based blended powder for powder metallurgy would cause the carbon to segregate from the iron powder due to the difference in their specific gravity during the transportation of the blended powder or at the time of the feed of the same, thus raising such a problem that sintered articles have variations in sliding properties.
Furthermore, the technique set forth in Japanese Patent Laid-Open Publication No. Hei 8-144026 was intended to obtain as high a toughness as the present invention, however, it has disclosed no data on the sliding property.
DISCLOSURE OF THE INVENTION
Hereupon, the object of the present invention is to overcome the aforementioned prior art problems. It is to provide an iron based blended powder for powder metallurgy that can provide, after sintering, a good reformable sintered article having less variation in properties, which contains Cr for providing a higher wear resistance, has a good sliding property, and has a good impact resistance with an impact value of 6J/cm
2
.
As the result of intensive study, the present inventors completed the present invention with the findings that the iron based blended powder was suitable as a blended powder for powder metallurgy that can provide, after sintering, a good reformable sintered article having less variation in properties, which contains Cr for providing a higher wear resistance, has a good sliding property, and has a good impact resistance with an impact value of 6J/cm
2
, which was formed by adhering compounds containing a graphite powder and B to the surface of an atomized alloy iron powder containing Mn, Cr, and S, and containing Mo and V selectively, and was further blended with a Ni powder, a Cu powder, and a lubricant.
(1) An iron based blended powder for powder metallurgy, formed by an atomized alloy iron powder with 0.01% to 1.0% of one or more types of compounds containing B, 1 to 10% of Ni powder, 1 to 6% of Cu powder, 1.3 to 3.0% of graphite powder, by weight % with respect to the total weight of said atomized alloy iron powder, the compound powder containing B, the Ni powder, the Cu powder, and the graphite powder, as well as 0.5 to 2.0 parts by weight of a lubricant with respect to 100 parts by weight of said total weight, the iron based blended powder for powder metallurgy being characterized in that said atomized alloy iron powder comprises, by weight %, 0.03 to 1.00% of Mn, 0.5 to 4.0% of Cr, 0.03 to 0.3% of S, and the residue of Fe and unavoidable impurities, said compound powder containing B and said graphite powder being adhered by means of said lubricant to surfaces of said atomized alloy iron powder.
(2) An iron based blended powder for powder metallurgy according to claim (
1
), characterized by further containing one or two types of elements selected from the group consisting of 0.05% to 3% of Mo and 0.1 to 0.5% of V.
(3) An iron based blended powder for powder metallurgy according to claim (
1
) or (
2
), characterized in that said blended powder satisfies the following equations of (1) and (2):
the content of C of a blended powder 75 to 150 &mgr;m in a particle diameter/the content of C of the whole blended powder≧0.5 (1),
and
the content of B of a blended powder 75 to 150 &mgr;m in a particle diameter/the content of B of the whole blended powder≧0.5 (2).
The iron based blended powder for powder metallurgy according to the present invention allows, after sintering, the sintered article to contain the content of free carbon of 1% by weight or more. In addition, the iron based blended powder for powder metallurgy makes available a reformable sintered article which has 7.0 kgf/cm
2
or more of the maximum allowable load, which has a sliding property in a dried wearing condition, 1.0 kgf/cm
2
of the variation in the sliding property (equal to 1 &sgr; of the standard deviation), and an impact value of 6J/cm
2
.
Now, the reason why Mn, Cr, and S, which are contained as preparatory alloys in the atomized alloy iron powder to be used in the present invention, are limited is explained.
The Content of S in the Iron Powder: 0.03 to 0.3% by Weight
This was added to produce free graphite in the sintered article. The S in the iron powder is present as FeS on the surface of the iron powder, having an effect of reducing the surface energy of the iron powder. With a content of S below 0.03% by weight, no effect of increasing the content of free graphite is recognized. On the other hand, with a content of S above 0.3% by weight, the sintered article has a low impact value and further soot is produced that causes the sintered article to be apt to corrosion. In addition, the sintering furnace will be damaged. For this reason, the content of S was limited to 0.03% to 0.3% by weight. It is preferably 0.05% to 0.25% by weight.
The Content of Cr in the Iron Powder: 0.5 to 4.0% by Weight
Cr was added to increase the wear resistance of the sintered article and to reduce the frictional coefficient. With a content of Cr below 0.5% by weight, no effect of the addition can be obtained. However, with a content of Cr above 4.0% by weight, the sintered article becomes too hard to be reformable and to cause the toughness to decrease. For this reason, the content of Cr was limited to 0.5% to 4.0% by weight. It is preferably 0.5% to 2.5% by weight.
The Content of Mn in the Iron Powder: 0.03 to 1.0% by Weight
Mn is an element for reducing free graphite in the sintered article. However, when Cr and S
Uenosono Satoshi
Yang Ji-bin
Kawasaki Steel Corporation
Mai Ngoclan
Oliff & Berridg,e PLC
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