Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Patent
1987-09-11
1989-02-14
Terapane, John F.
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
420 92, 420119, C22C 3808
Patent
active
048044091
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an alloy steel powder for powder metallurgy used in the manufacture of various sintered parts.
BACKGROUND ART
It has hitherto been known that sintered materials are obtained by using pure iron powder as a main starting material. However, the tensile strength of such a sintered material is about 30-40 kgf/mm.sup.2, which is a low level of mechanical strength, so that the application thereof is undesirably restricted to low load pulleys and the like.
As a means for solving the above drawback, there is developed a technique of utilizing an alloy steel powder obtained by soluting various alloying ingredients such as Mn, Ni, Cr and Mo into powdery particles (for example, reference may be made to Japanese patent application publication No. 49-28,827).
In such an alloy steel powder, however, it is possible to raise the strength of steel powder itself through alloying, but the plastic deformation in the forming process becomes difficult with the rise of the strength to impede the compressibility, and it is necessary to degrade the strength of the sintered body due to the reduction of the sintered density. Therefore, the resulting sintered body has not sufficient mechanical properties.
DISCLOSURE OF INVENTION
In order to attempt the improvement of the strength by alloying, therefore, it is important to select alloying ingredients and their composition ranges so as not to impede the compressibility of the ferrous powder as far as possible.
As the other important properties in sintered mechanical parts obtained through molding-sintering-heat treatment, there are mentioned a hardened dimensional deviation through heat treatment after the sintering and a hardness.
In general, it is appropriate to select alloying ingredients giving excellent hardenability for providing sufficient hardness. On the other hand, the strain through heat treatment is mainly caused by the amount of phase transformation in the heat treatment, i.e. the amount of martensitic transformation and the microscopic or macroscopic scattering of residual austenite, so that the hardening transformed dimensional deviation becomes generally larger in the composition having good hardenability, which tends to make the change of shape and size large.
Up to now, the planning of steel powder is exclusively made from viewpoints of mechanical properties of the sintered body such as hardness, strength, toughness and so on. On the other hand, sufficient examinations are not made from a viewpoint of effective steel powder composition for powder metallurgy capable of reducing the strain through heat treatment after sintering and improving the hardness of the sintered body.
For instance, Japanese Patent Application publication No. 55-36,260 discloses an Fe-base sintered body containing Ni and W or Ni, W and Mo and a method of producing the same. The invention disclosed in this publication is designed to obtain high strength, high toughness sintered bodies by fundamentally mixing iron powder with metal powders as an alloying ingredient.
This invention is developed under the aforementioned situations, and is to propose alloy steel powders for powder metallurgy which are easy in plastic deformation during forming, excellent in compressibility, high in sintered density, less in hardened dimensional deviation through heat treatment, high in hardness after heat treatment of the sintered body and useful as a starting material for the sintered body requiring high strength and hardness in gears of automobile transmissions or the like.
The inventors have made various studies in order to solve the above problems and found that the foregoing objects are advantageously achieved by utilizing W and Ni, and further Mo or Cu as an alloying ingredient for steel powder. The invention is based on this finding.
That is, the essential construction of the invention is as follows.
(i) An alloy steel powder for powder metallurgy, consisting of W: 0.2.about.2.0 wt % (hereinafter simply shown as %), Ni: 0.8.about.3.0% and the balance being substan
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Abe Teruyoshi
Kawano Masaki
Ogura Kuniaki
Takajo Shigeaki
Jorgensen Eric
Kawasaki Steel Corporation
Miller Austin R.
Terapane John F.
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