Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2000-07-18
2002-02-19
Jenkins, Daniel J. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S255000, C419S031000, C419S038000, C419S046000, C148S513000
Reexamination Certificate
active
06348080
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a chromium base alloy steel powder. More specifically the invention concerns a low oxygen, low carbon alloy steel powder including in addition to iron and chromium also Mo and Mn as well as the preparation thereof. The invention also concerns a method of preparing sintered components from this powder as well as the sintered components.
BACKGROUND OF THE INVENTION
There have recently been developed various techniques for strengthening materials for sintered machine parts produced from various alloy steel powders through powder metallurgy. The use of the alloying elements chromium, molybdenum and manganese in low oxygen, low carbon iron powders has been suggested in e.g. the U.S. Pat. No. 4,266,974 and EP 0 653 262. The base material for the powder in both publications is a water atomised and reduction-annealed powder. The US publication discloses that the most important step in order to obtain a powder having low oxygen and carbon contents is the annealing step, which preferably should be performed under reduced pressure, specifically by vacuum induction heating. The U.S. patent also discloses that other methods of reduction annealing involve drawbacks limiting their commercial scale installation. Nothing is disclosed in the EP application about the reduction annealing. The effective amounts of the alloying elements according to the US patent are between 0.2 and 5.0% by weight of chromium, 0.1 and 7.0% by weight of molybdenum and 0.35 and 1.50% by weight of manganese. The EP publication discloses that the effective amounts should be between 0.5 and 3% by weight of chromium, 0.1 and 2% by weight of molybdenum and at most 0.08% by weight of manganese. The purpose of the invention according to the U.S. patent is to provide a powder satisfying the demands of-high compressibility and moldability of the powder and good heat-treatment properties, such as carburising, hardenability, in the sintered body. A serious drawback when using the invention disclosed in the EP application is that cheap scrap cannot be used as this scrap normally includes more than 0.08% by weight of manganese. In this context the EP application teaches that a specific treatment has to be used in order to reduce the Mn content to a level not larger than 0.08% by weight. Another problem is that nothing is taught about the reduction annealing and the possibility to obtain the low oxygen and carbon content in water-atomised iron powders including elements sensitive to oxidation, such as chromium, manganese. The only information given in this respect seems to be in example 1, which discloses that a final reduction has to be performed.
REFERENCES:
patent: 4069044 (1978-01-01), Mocarski et al.
patent: 4234168 (1980-11-01), Kajinaga et al.
patent: 4266974 (1981-05-01), Nitta et al.
patent: 4382818 (1983-05-01), Mocarski
patent: 0653262 (1995-05-01), None
patent: WO 9803291 (1998-01-01), None
Arvidsson Johan
Eriksson Ola
Burns Doane Swecker & Mathis L.L.P.
Hëganäs AB
Jenkins Daniel J.
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