Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Plural heating steps including sintering
Reexamination Certificate
1997-05-13
2001-03-20
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Plural heating steps including sintering
C419S055000
Reexamination Certificate
active
06203753
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods of making metal parts from metal powder compositions comprising an iron base metal powder and an amide lubricant. The sintered metal parts have improved physical and mechanical properties.
BACKGROUND OF THE INVENTION
Metal parts can be prepared using powdered metallurgy (P/M) from powdered metal compositions by methods known within the industry. These parts can be formed in shapes which would be difficult to form by other methods. Many applications for parts formed from P/M processes require high strength and dynamic properties. It is necessary to re-engineer or increase the density of the composition to meet the requirements. However, the methods available for obtaining high density, high strength parts by P/M processes such as high temperature sintering, double-press and double-sintering processes, and liquid phase sintering have been found to have inherent limitations.
Recently, U.S. Pat. No. 5,154,881 disclosed a composition which provided a single compaction method for obtaining high density parts. This patent utilizes an iron-based metal powder composition containing an amide lubricant. The lubricant is a reaction product of a monocarboxylic acid, a dicarboxylic acid, and a diamine. The composition, metal and lubricant, is compacted in the die of the temperature of up to about 690° F., and preferably in a range of 300-500° F., at a pressure of about 35-60 tons per square inch (tsi). Further disclosed is the fact that the composition can be warm-pressed at a temperature of about 300° F. However, the properties achieved using the materials and method described in this patent are not sufficient to meet the needs of all applications.
Therefore, a need exists to develop a process for preparing parts which have improved impact strength and tensile properties. Parts which have these properties would be expected to have longer life and be less subject to wear.
SUMMARY OF THE INVENTION
The present invention provides a method for making a sintered part from a metal powder composition comprising an iron-based metal powder and an amide lubricant. The method comprises the steps of compacting the metal powder composition, pre-sintering the compacted composition, recompacting the compacted and pre-sintered composition, and sintering the recompacted composition. The invention also contemplates parts having improved properties prepared by the method of the invention.
The method of the subject invention is useful with any iron-based powder composition using an amide lubricant. The iron-based powder refers to any iron-containing particles generally used in the practice of powder metallurgy including, but not limited to, particles of substantially pure iron; particles of iron in admixture with, for example, particles of alloying elements such as transition metals and/or other fortifying elements; and pre-alloyed iron particles.
The amount of lubricant to be used can be up to about 15 weight percent of the composition, based on the total weight of metal powder and lubricant. A preferred embodiment contains from about 0.1 to about 10 weight percent lubricant. Because the lubricants of this invention are reaction-product mixtures, they melt over a temperature range that can encompass a wide range. Depending on the particular lubricant used, melting will commence at a temperature between about 300° F. and 500° F., and the lubricant mixture will be completely melted at some temperature up to 500° F. above this initial melting point.
REFERENCES:
patent: 4955798 (1990-09-01), Musella et al.
patent: 5154881 (1992-10-01), Rutz et al.
patent: 163161 (1949-03-01), None
Jones, W.D. “Fundamental Principles of Powder Metallurgy”, Edward Arnold Publishers, Ltd. 1960, pp. 844-848.
Darby & Darby
Jenkins Daniel J.
The Presmet Corporation
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