Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Post sintering operation
Patent
1994-08-25
1996-04-30
Walsh, Donald P.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Post sintering operation
419 11, 419 32, 419 23, 419 36, 419 39, 419 38, 419 56, 419 58, 419 60, 419 29, 419 37, B22F 312
Patent
active
055122361
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a process of coining sintered articles to final shape and in particular relates to a process of precision coining sintered articles of powder metal having a composition of between 0.3% to 2.0% manganese, 0.2 to 0.85% carbon with the remainder being iron and unavoidable impurities where the sintered articles are coined to final shape so as to narrow the tolerance variability of the coined articles.
BACKGROUND TO 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 compressabilities 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 filled with a compact moist mass of metallic powder and finally completing the hard metallic particle thus formed by sintering.
U.S. Pat. No. 4,707,332 teaches a process for manufacturing structural parts from intermetallic phases capable of sintering by mea
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Jones Peter
Lawcock Roger
Gierczak Eugene J. A.
Greaves John N.
Stackpole Limited
Walsh Donald P.
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