Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1989-07-14
1990-09-04
Lechert, Jr., Stephen J.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
75255, 1481261, 148127, 148143, 419 23, 419 35, 428570, 420119, C22C 100
Patent
active
049541714
DESCRIPTION:
BRIEF SUMMARY
Technical Field
The present invention relates to an alloy powder to be used for the production of sintered parts by powder metallurgy and also to a high-strength sintered alloy steel to be produced by heat treatment after sintering.
Background art
Iron-based sintering materials are in general use for automotive parts and others. Recently, these parts are required to be lighter and stronger than before.
It is known that various kinds of alloy steel powders are used to produce sintered parts having high strength. More often than not these high-strength sintered parts are required to have a high density. To meet this requirement, attempts are being made to increase the compressibility of steel powder by using steel powder in the form of composite alloy steel powder which is produced by attaching by diffusion powder particles of alloy elements to part of the surface of iron powder particles, because the particles of completely uniform alloy steel powder are hard
Even in the case of these composite alloy steel powders, it is impossible to obtain sintered bodies having satisfactory properties unless the alloy composition thereof is adequate or unless they are prepared and used adequately.
An attempt to increase the strength of sintering materials by increasing the amount of the alloying element has been made according to Japanese Patent Laid-open No. 231102/1986. A disadvantage of such high alloy steel (containing more than 7% of Ni) is that it is high in production cost and it has such high hardness after sintering that it does not permit sizing and cutting. An additional disadvantage is that it contains a large amount of residual austenite after sintering. This makes it necessary to perform special heat treatment such as sub-zero treatment if a high strength (in terms of tensile strength higher than 130 kgf/mm.sup.2) is to be obtained. This leads to a cost increase. In addition, the residual austenite decomposes with the lapse of time, causing the deformation of parts.
There is disclosed in Japanese Patent Publication No. 9649/1970 a low alloy steel powder which provides high-strength sintered bodies which undergo less dimensional changes during heat treatment performed after molding. This low alloy steel powder is obtained by heating a mixture of iron powder and compounds of Ni, Mo, and Cu, thereby attaching by diffusion the alloy components, crushing agglomerated particles, and annealing thus obtained particles. A disadvantage of this low alloy steel powder is that it contains 0.50-2.00 wt. % of Cu, which segregates on the grain boundary, forming an .epsilon.-Cu brittle layer, which aggravates the mechanical properties.
One of the present inventors proposed a composition for composite alloy steel powder which is suitable in the case where the sintered body is used as such without any post heat-treatment. (See Japanese Patent Laid-open No. 89601/1988.) This alloy steel powder contains Ni and/or Cu and Mo, and the alloy composition imparts high hardness and dimensional stability to the sintered body. However, it does not afford any sintered body which has a tensile strength higher than 130 kgf/mm.sup.2.
Further, one of the present inventors and another proposed a composite alloy steel powder composed of steel powder and two or more alloy components attached by diffusion to the surface of the steel powder particles, with the content of each alloy component in the steel powder of particle diameter smaller than 44 .mu.m being in the range of 0.9-1.9 times the average content in the entire steel powder (See Japanese Patent Laid-open No. 130401/1986.) This alloy steel powder, however, does not provide any sintered body which has a tensile strength higher than 130 kgf/mm.sup.2. This is because the sintered body does not undergo strain-induced transformation from austenite to martensite when it is pulled, and it does not have a high density due to insufficient compressibility.
Sintered parts are given high internal toughness, high surface abrasion resistance, and high fatigue strength by carburizing quenching. Th
REFERENCES:
patent: 3887402 (1975-06-01), Kondo et al.
patent: 3901661 (1975-08-01), Kondo et al.
patent: 4655853 (1987-04-01), Byrnes et al.
Abe Teruyoshi
Furukimi Osamu
Maruta Kei-ichi
Ogura Kuniaki
Sakurada Ichio
Bhat Nina
Kawasaki Steel Corp.
Lechert Jr. Stephen J.
Miller Austin R.
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