Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0257—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements
  • C22C33/0264—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 5%
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
  • B22F1/17—Metallic particles coated with metal
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C33/00—Making ferrous alloys
  • C22C33/02—Making ferrous alloys by powder metallurgy
  • C22C33/0207—Using a mixture of prealloyed powders or a master alloy

Definitions

• This invention relates to a method of making powder compacts.
• Powdered metal compacts have been used in some industrial applications, but have not generally found full acceptance because the extra method steps and the added cost required to obtain a reasonable strength level and density in the powdered metal compact have been excessive-, particularly when compared to similar parts obtained by melt formation.
• the conventional commercial mode of processing powdered metal to form compacts typically comprises (a) blending and milling together selected ponder elements in the presence of a lubricant, (b) compacting the mechanicelly blended charge (c) heating the compact under a reducing atmosphere for a period of 30 min. at 810°C to volatilize the lubricant, and (d) sintering the compact at an appropriate temperature.
• This has resulted at best in a green density prior to sintering of about 79-86% and a sintered density of 80-89% of theoretical. A higher density level would require additional hot forging to increase the strength level and reduce porosity.
• a method of producing a metal powder compact which comprises compacting metal powder in the presence of from 1 to 5% by weight of a low-melting point metal at a temperature sufficient to melt , the low-melting point metal.
• 1-5%, preferably 2-4% of a low melting metal ingredient is added to a coarse or fine iron powder and the mixture is subsequently warm- briquetted (preferably at a temperature of 450-650°F) to form a liquid phase of said addition agent while consolidating the powder.
• a low melting metal ingredient preferably selected from copper-tin, copper-lead, and lead
• the particle size of the base iron powder is preferably relatively fine (4-5 microns) and about 2.5% of a liquid phase promoting ingredient, particularly tin, is preferably added thereto, the blended mixture has warm briquetted at a temperature of from 450 to 650°F.
• the compact may then be sintered.
• a cryogenically-produced fine powder is used as the source of the powdered metal.
• the present invention includes two preferred embodiments:-(I) the addition of 1-5% of a low-melting metal, such as which results, after warm briquetting, in a compact having 25% less porosity and increased strength compared with a conventional cold briquetted compact; and (II) the adaition of 1-5% of a low melting metal, such as tin or lead, to a fine particle sizeiron powder, which results, after warm briquetting and sintering, in a product having only 3% porosity compared with 20% porosity when tin or lead is not used.
• the unprecedented strength and density level of the warm briquetted compact makes it possible to produce certain powder metal parts without sintering, resulting in significant energy savings.
• Candidate parts would be heat sinks (such as diodes) and steering column collars.
• With respect to the 97% dense sintered powder product it can be produced with existing equipment (no forging) which represents a major potential for a new class of powder metal business.
• a preferred method for carrying out the first aspect of this invention is as follows:
• This step is to transfer, by impact, a portion of the tin ingredient, carried by the ball milling elements, to form a tin shell about substantially each particle of the powder.
• the coating is generated by abrasion or scratching of the powder particle against the surface of' the ball milling elements. This obviously is accomplished by rotating the housing of the ball mill machine to impart a predetermined abrading force from the balls.
• the ball milling operation will cold work or generate defect sites in substantially all of the powder particles above 124 microns; since the majority of the particles selected for the process will be below said size range, they will generally be free of cold work or defect sites.
• Theball milling operation should be carried sufficiently long so that substantially each particle will be fully coated; this requires statistically a minimum period of time so that tin coating will preferably be continuous.
• the particles will be in a condition where they will all substantially have a continuous tin envelope (coating or shell).
• the shell should preferably be an impervious continuous envelope about each particle, it is not critical that it be absolutely impervious.
• the dry impact coatediron particles are then subjected to a heating treatment while an agglomerating pressure is applied.
• Heat is applied to raise the temperature of the mass of particles to a level slightly above the melting temperature of the metal coating, whichsbould be in the range of 450-650 F, 419°F being necessary to melt pure tin, 446°F being necessary to melt an alloy of 99.6% tin and .4% copper, a melting temperature of 594°F is necessary to melt an alloy of 95% lead and 5% tin, and a melting temperature of 561°F is necessary to melt an alloy of 63% tin and 37% lead and a melting temperature of 618°F is necessary to melt pure lead.
• the warm briquetting temperature could be mised to as much as 1350°F (723°C) if necessitated by the requirement to melt the metal coating, or to improve densification by plastic deformation 450-1358°F encompass warm briquetting herein.
• the pressure applied shoulu be no more than 30 tsi (and preferably in the range of 10-30 tsi) so that wear on the tooling used for agglomeration is reduced to a minimum.
• Agglomerition or compaction may be-carried. out by a conventional press to obtain the maximum desired densities herein.
• Compact densities herein are considerably improved to 80% or more of theoretical density.
• solie tin or low melting envelope about the particles inproves conpressibility acting as a lubricant, and the liquified metal phese acts as a pore filler during the compaction operation.
• a density of about 82% of theoretical or 6.4 gr. per cubic centimeter is typically obtained using a compressive force of about 30 tsi; with a dry impact coated pewder herein densities of about 7.0 gm. per cubic centimeter can be obtained at the same force level.
• the first method is varied in either or both of two respects.
• the iron powder selected is limited to a fine particle size, averaging 4-5 microns. This can preferably be obtained by extracting the iron powder as a by-product of processing of scrap or machining chips from industrial metal work.
• scrap metal in the form of machine turnings are segregated or selectad.
• Machine turnings are segments of ribbons of low carbon or alloy steel; the turnings should be selected to have a surface to volume ratio of at least 60:1.
• the machine turnings may be shavings cut from alloy bar, and the bar may have a chemistry which includes alloying ingredients such as manganese, silicon, chromium, nickel and molybdenum.
• the turnings will have a size characterized by a width of .1-1.0", thickness of .005-.03"m and a length of 1-100".
• Machine turnings are usually not suitable for melting in an electric furnace because they prevent efficient melt down due to such surface to volume ratio.
• the turnings should be selected to be generally compatible in chemistry when in the final product; this is achieved optimally when the turnings are selected from a common machining operation where the same metal stock was utilized in forming all the turnings.
• the selected scrap pieces are put into a suitable charging passage leading to a ball milling machine (or equivalent impacting device).
• an ingredient for freezing the metal pieces is introduced, such as liquid nitrogen; it is sprayed directly onto the metal pieces. Mere contact of the liquid nitrogen with the scrap pieces will freeze them instantly.
• the liquid nitrogen should be applied uniformly throughout its path to the point of impaction.
• the ballnilling elements are motivated preferably by rotation of the housing to contact and impact the frozen pieces of scrap metal causing them to fracture and be comminuted. Such impaction is carried out to apply a sufficient fracturing force for a sufficient period of time and rate to reduce said scrap pieces to a powder form.
• the resulting powder will be layered or flake in configuration and typically have both coarse and fine powder proportions.
• a typical screen analysis for a cryogenic powder would be as follows (for a 100 gm. sample):
• the method is varied in another important aspect: the compact or briquetted product is subjected to sintering.
• This treatment can be carried out in a conventional sintering furnace with heating to a temperature preferably about 2000°F.
• the temperature to which the briquetted or compact is heated should be at least to the plastic region for the metal constituting the powder.
• a controlled or protective atmosphere may be maintained in the furnace, preftrably consisting of inert or reducing gases.
• Whith sintering a final density of about 97% has been achieved without the necessity for secondary consolidation such as forging. This is an extremely high density for a process which is essentially two step and devoid of secondary consolidation. Since the compact does not contain a volatile lubricating agent, such as Acrowax, the delubrication step is eliminated from the process or from the zone in a sintering furnace. The resulting mechanical properties for such a sintered product would be as follows: tensile strength 115,000 psi, % elongation 10%, and hardness R B 78.
• Table I Test results to support the above methods are depicted in Table I.
• an iron powder specimen identified as Atomet 28 was employed which has a chemistry of 99.8% Fe 0.05%C and an average particle size of 70-80 microns.
• the second powder specimen consisted of carbonyl powder, having a chemistry of 99.9% Fe 0.1%C and a particle size range of 4-5 microns.
• Tin was employed in amount of 2.5% weight percentage of the powder mass. This required ball milling to be carried out for a period of 48 hours to achieve a coating thickness of about 0.1 micron.
• Each powder specimen was heated to a temperature level of 473°F.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Powder Metallurgy (AREA)

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• 1979
  • 1979-09-28 CA CA000336663A patent/CA1151384A/en not_active Expired
  • 1979-11-12 JP JP14637879A patent/JPS5573801A/ja active Granted
  • 1979-11-21 EP EP79302649A patent/EP0011981B1/de not_active Expired
  • 1979-11-21 DE DE7979302649T patent/DE2966491D1/de not_active Expired

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