Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Special medium during sintering
Patent
1994-01-14
1995-12-19
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Special medium during sintering
419 8, 419 11, 419 12, 419 13, 419 14, 419 23, 419 25, 419 26, 419 29, 419 39, 419 53, 419 58, 419 35, B22F 316
Patent
active
054766320
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a method or process of forming a sintered article of powder metal, and particularly relates to a process of forming a sintered article of powder metal by blending combinations of finely ground ferro alloys (either singly or in combination with other ferro alloys) with elemental iron powder and other additives and then high temperature sintering of the article in a reducing atmosphere to produce sintered parts with oxygen contents less than 250 parts per million (ppm). More particularly the ferro alloys admixed to the base iron have a mean particle size of approximately 8 to 12 microns, having previously been ground to size in a inert atmosphere.
BACKGROUND OF THE INVENTION
Powder metal technology is well known to the persons skilled in the art and generally comprises the formation of metal powders which are compacted and then subjected to an elevated temperature so as to produce a sintered product.
Conventional sintering occurs at a maximum temperature of approximately up to 1,150.degree. C. Historically the upper temperature has been limited to this temperature by sintering equipment availability. Therefore copper and nickel have traditionally been used as alloying additions when sintering has been conducted at conventional temperatures of up to 1,150.degree. C., as their oxides are easily reduced at these temperatures in a generated atmosphere, of relatively high dew point containing CO, CO.sub.2 and H.sub.2. The use of copper and nickel as an alloying material is expensive. Moreover, copper when utilized in combination with carbon as an alloying material and sintered at high temperatures causes dimensional instability and accordingly the use of same in a high temperature sintering process results in a more difficult process to control the dimensional characteristics of the desired product.
Manufacturers of metal powders utilized in powder metal technology produce prealloyed iron powders which are generally more difficult to compact into complex shapes, particularly at higher densities (>7.0 g/cc). Manganese and chromium can be incorporated into prealloyed powders provided special manufacturing precautions are taken to minimize the oxygen content, for example, by oil atomization. Notwithstanding this, these powders still have poor compressibilities compared to admixed powders.
Conventional means to increase the strength of powder metal articles use up to 8% nickel, 4% copper and 1.5% molybdenum, in prealloyed, partially prealloyed, or admixed powders. Furthermore double press double sintering can be used for high performance parts as a means of increasing part density. Conventional elements are expensive and relatively ineffective for generating mechanical properties equivalent to wrought steel products, which commonly use the more effective strengthening alloying elements manganese and chromium.
Moreover, conventional technology as disclosed in U.S. Pat. No. 2,402,120 teach pulverizing material such as mill scale to a very fine sized powder, and thereafter reducing the mill scale powder to iron powder without melting it.
Furthermore, U.S. Pat. No. 2,289,569 relates generally to powder metallurgy and more particularly to a low melting point alloy powder and to the usage of the low melting point alloy powders in the formation of sintered articles.
Yet another process is disclosed in U.S. Pat. No. 2,027,763 which relates to a process of making sintered hard metal and consists essentially of steps connected with the process in the production of hard metal. In particular, U.S. Pat. No. 2,027,763 relates to a process of making sintered hard metal which comprises producing a spray of dry, finely powdered mixture of fusible metals and a readily fusible auxiliary metal under high pressure producing a spray of adhesive agent customary for binding hard metals under high stress, and so directing the sprays that the spray of metallic powder and the spray of adhesive liquid will meet on their way to the molds, or within the latter, whereby the mold will become fille
REFERENCES:
patent: 4885133 (1989-12-01), Fujii
patent: 4966626 (1990-10-01), Fujiki et al.
patent: 5154881 (1992-10-01), Rutz et al.
Jones Peter
Shivanath Rohith
Gierczak Eugene J. A.
Greaves John N.
Stackpole Limited
Walsh Donald P.
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