Metal treatment – Process of modifying or maintaining internal physical... – Carburizing or nitriding using externally supplied carbon or...
Patent
1993-07-28
1995-08-15
Roy, Upendra
Metal treatment
Process of modifying or maintaining internal physical...
Carburizing or nitriding using externally supplied carbon or...
75247, B22F 100, B22F 300
Patent
active
054415799
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of treating steel particles to produce abrasive grit, and a grit which is a product of the described method. In one aspect of the present invention, the grit, thus, produced is ground into a powder and is further treated to reduce the carbon and oxygen content thereof, so that it is suitable for use in a subsequent sintering operation.
2. Prior Art
In the powdered metal industry, many types of parts may be formed from sintering powdered metal. Metal powder such as that formed from, e.g., steel, is used in the formation of many types of articles of manufacture. This powder is subjected to a variety of processes in order to covert the powder into an article such as, e.g., a gear. Articles of this type each have a measurable hardness, ductility, tensile strength and a variety of other physical characteristics that allow the created articles to be acceptable for a given application.
The metallic powder which is used in the production of these types of articles has a direct impact upon the quality of the finished article. More specifically, the physical characteristics of the article are usually determined by the cleanliness and purity of the powder which, in turn, is related to the powder's overall oxygen content. Generally, for many high performance applications, a steel powder is required which has a relatively low oxygen content in order to produce an article having a high degree of strength. In addition, a low carbon content is often preferable.
U.S. Reissue Pat. No. Re-22,452, issued Mar. 7, 1944 to Clements et al describes a method of making powdered iron or steel in which shredded steel scrap is passed through a carburizing furnace, a quench tank, and a dryer and subsequently is ground up, sorted according to size, and then annealed by passing it through a suitable annealing furnace in which the material is protected by a neutral or reducing atmosphere. However, Clements does not suggest using the grit, which is an intermediate product of the process, for any end use. In addition, the method of Clements does not require cleaning of the feedstock prior to processing.
While the use of metal powders in forming machine parts and the like is a known process, improvements in this process are continuously being sought. In particular, a method of producing a metal powder which is suitable for use in a subsequent sintering operation and which includes components such silicon, manganese, chromium, or vanadium in which oxidation of those compounds is avoided would contribute to the art of powder metallurgy.
SUMMARY OF THE INVENTION
The present invention provides (1) a method of producing an abrasive steel grit material and (2) a steel grit which is the product of the described method.
The method of producing grit in accordance with the present invention, generally, comprises the steps of:
(a) heating clean, dry steel particles in a protective atmosphere which is substantially non-oxidizing at a temperature of about 1500.degree. to about 1800.degree. F. (815.degree. to 1180.degree. C.) until the steel particles attain a carbon content of at least 0.3 percent by weight;
(b) quenching the heated steel particles with water to cause the particles to become brittle;
The present invention also provides a method of producing steel powder from the grit, by an annealing process which is suitable for use in a subsequent sintering operation, the steel powder having a low oxygen content. This subsequent powder production, in a preferred embodiment thereof, includes a preoxidation of the powder prior to annealing to facilitate later decarburization of the powder. By using the method of the present invention, steel scrap which contains easily oxidizable constituents, such as silicon, chromium, and magnesium can effectively be used to produce a steel powder which contains minimum amounts of oxides of the above-identified materials, and which is usable to produce sintered parts.
For a more complete understanding of the present inven
REFERENCES:
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Metals Handbook Ninth Edition, vol. 7. p. 361 discussing production sintering practices.
"Production Sintering Atmospheres" by H. S. Nayar in Metals Handbook, Ninth Edition at pp. 339-350.
Kaufman Sydney M.
LeBeau Stephen E.
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