US3528081A - Method of making steel powder - Google Patents

Method of making steel powder Download PDF

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Publication number
US3528081A
US3528081A US698738A US3528081DA US3528081A US 3528081 A US3528081 A US 3528081A US 698738 A US698738 A US 698738A US 3528081D A US3528081D A US 3528081DA US 3528081 A US3528081 A US 3528081A
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United States
Prior art keywords
sulphur
steel
particles
powder
sintered
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Expired - Lifetime
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US698738A
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English (en)
Inventor
Robert A Huseby
Paul B Garner
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AO Smith Corp
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AO Smith Corp
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    • 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%
    • C22C33/0271—Making ferrous alloys by powder metallurgy characterised by the range of the alloying elements the maximum content of each alloying element not exceeding 5% with only C, Mn, Si, P, S, As as alloying elements, e.g. carbon steel
    • 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
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/02—Making metallic powder or suspensions thereof using physical processes
    • B22F9/06—Making metallic powder or suspensions thereof using physical processes starting from liquid material
    • B22F9/08—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying
    • B22F9/082—Making metallic powder or suspensions thereof using physical processes starting from liquid material by casting, e.g. through sieves or in water, by atomising or spraying atomising using a fluid

Definitions

  • the invention relates to a method of making steel powder having, when compacted and sintered, increased machineability. Sulphur is added to carbon steel in the furnace and/or ladle in an amount of about .08 to .25% by weight of the steel.
  • the molten steel is fed by gravity from a tundish in the form of a downwardly moving stream and sheets of water are impinged against the stream to atomize the molten steel and provide a plurality of chain-like agglomerates of particles contain ing fine, dispersed inclusions of sulphur.
  • the particles are subsequently annealed at a temperature of 1500 F. to 2100 F. in a reducing atmosphere to soften the steel particles, reduce the oxide film and decrease the carbon content.
  • the resulting metal part has improved machineability due to the sulphur dispersions which are locked within the steel particles.
  • metal powder can be prepared by electrolytic processes, ore reduction processes, or by air or water atomization processes, such as that described in U.S. Pat. 3,325,277.
  • molten steel having a carbon content less than 1.8%, is fed by gravity from a tundish in the form of a downwardly moving stream.
  • a series of flat sheets of water are impinged against the stream of molten steel at an angle to thereby atomize the molten stream and provide a plurality of chain-like agglomerates of spheroidal particles.
  • the particles are heated or annealed to a temperature of about l500 F. in a reducing atmosphere for a period of time sufiicient to soften the particles and reduce the carbon content to a value less than 005%.
  • the particles are subjected to hammer milling to break up the cake-like structure formed during the anneal and restore the asatomized particle size.
  • the steel powder formed according to the method of Pat. 3,325,277, when compacted and sintered, has a high density and superior physical properties.
  • the steel powder such as that produced by the process of the above patent, is generally used for the production of metal parts having complex contours or shapes, for the powder can be molded to the complex shape, and machining of the part is thereby minimized.
  • powder metallurgy processes are designed to eliminate or minimize machining, most powder metallurgy parts nevertheless require some minor machining such as tapping of threads, drilling of holes, undercutting, and the like.
  • the present invention is directed to an improvement to the process described in Pat. 3,325,277 and is directed to the production of steel powder, which when compacted and sintered, has increased machineability.
  • sulphur is added to the mol ten steel, either in the furnace and/or the laddle.
  • the molten steel containing the sulphur in solution is fed by gravity from a tundish in the form of a 3,528,081 Patented Sept. 8, 1970 downwardly moving stream.
  • a series of sheets of water are impinged against the stream of molten steel and act to immediately quench and atomize the steel to provide a plurality of clump-like agglomerates of particles. Due to the very rapid quench involved.
  • the sulphur ispresent in the form of fine dispersions throughout the steel particles and large inclusions of sulphur are eliminated.
  • the particles are annealed at an elevated temperature and the annealing not only acts to soften the particles and reduce the carbon content but also serves to burn off any residual sulphur which may be located on the surface of the steel particles.
  • the particles tend to bind together to provide a cake-like structure and following the anneal, the cake-like structure is broken up to restore the as-atomized particle size of the agglomerates.
  • the particles are compressed and sintered under conventional procedures and the resulting metal part has improved machineability due to the presence of the suhphur.
  • the particles can be compressed and sintered without any appreciable loss in physical properties.
  • the machined surface is extremely smooth and the chips are short and bright with no color discoloration due to heating.
  • FlG. l is a flow sheet indicating the process of the invention.
  • FIG. 2 is a schematic representation of the apparatus employed for atomizing the metal particles.
  • the molten steel to be used in producing the steel particles can be produced by any of the conventional steel making process, such as open hearth electric furnace, basic oxygen, and the like.
  • the steel contains less than 3.3% by weight, and preferably less than 2%. of total alloying elements and the carbon content is less than l.8% by weight, preferably less than 0.20%, and under most conditions in the range of 0.08 to 12% by weight.
  • the steel has a manganese content less than 0.60% and generally in the range of 0.15 to 0.40% and preferably in the range of 0.25 to 0.35%.
  • sulphur is added to the molten steel either in the furnace or in the laddle or in both the furnace and in the ladle.
  • the sulphur is added in an amount so that the atomized powder has a sulphur content in the range of 0.08 to 0.25% by weight and preferably in the range of 0.10 to 0.20%.
  • the amount. of sulphur added to the molten steel will be slightly in excess of the above range due to the fact that some sulphur will be lost during the steelmaking process.
  • the sulphur can be added to the molten steel in any desired form. It has been found that sulphur in the form of solid sticks are very satisfactory for the sticks can be completely immersed in the steel without any appreciable burning oil of the sulphur. As an alternate method, the sulphur can be added to the molten steel in the form of substantially pure pyrite, or elemental sulphur can be added as a liquid or as a powder.
  • the molten steel containing the sulphur is then introduced into tundish l at a temperature of about 3100 F. and the molten steel flows by gravity through the outlet slots or nozzles 2 in the form of a series of streams 3.
  • the process by which the steel is atomized can be similar to that described in Pat. 3,325,277 of Robert A. Huseby, entitled Method of Making Metal Powder.
  • water in the form of thin sheets or curtains 4 is directed against the stream 3 at an angle greater than 5 with respect to the axis of the stream and generally at an angle of 15 to from the vertical.
  • the temperature of the water employed in the atomization process is not critical and is generally less than 160 F.
  • the water employed during the atomization is under substantial pressure above 500 p.s.i. and for most operations above 1.000 p.s.i.
  • the water is directed toward the stream of molten metal in the form of a thin sheet having a thickness less than 0.075 inch and preferably less than 0.05 inch at the point of discharge from the nozzle.
  • the nozzle is designed so that the water sheets do not flare out to any appreciable extent but maintain the thickness when impinging against the molten steel stream.
  • the thin sheets of water act to atomize or particlize the steel and produce chain-like agglomerates of generally spheroidal particles.
  • the irregular shape of the agglomerated particles results in a higher green strength for articles subsequently made from the steel powder.
  • the sulphur is in solution in the molten steel and due to the rapid quenching brought about by the atomization,
  • the sulphur is trapped or locked in the individual particles in the form of fine dispersions.
  • the rapid quench prevents the dispersions of sulphur from accumulating in the form of large inclusions and it is believed that the fine dispersions which are locked within the individual particles is responsible for bringing about the improved machineability of the subsequently sintered parts without any appreciable loss in other physical properties.
  • the steel powder is subjected to an annealing treatment which serves to soften the particles, reduce the oxide film and substantially decrease the carbon content.
  • an annealing treatment which serves to soften the particles, reduce the oxide film and substantially decrease the carbon content.
  • any sulphur dispersions which are exposed on the surface of the particles will generally be burned off during the annealing treat;-
  • the annealed particles are free of external 3 sulphur.
  • the powder is heated to a temperature in the range of 1500 F. to 2100 F. and preferably 1650 F. to 1800 F. in a reducing atmosphere such as disassociated ammonia, hydrogen, or other conventional decarburizing reducing gases.
  • the annealing treatment serves to soften the steel particles as well as reducing the carbon content to a value to below 0.05% and generally to a value in the range of 0.001% to 0.020%.
  • the powder should be held at the annealing temperature for a period of at least 1.5 hours and preferably 2 hours.
  • the particles tend to cake together and the cake-like structure is broken up after the anneal by a hammermill process.
  • the hammermilling breaks up the sintered cake, while not breaking up the regular agglomerized nature of the particles, and restores the original atomized particle size. It is important to control the dewpoint in the annealing operation to prevent excessive caking of the particles. Preferably the dewpoint should be above 50 F. and below 80 F. in the last /3 of the hot zone of the furnace.
  • the resulting steel powder can be used to form any desired machine part or combination of parts by conventional powder metallurgy processes.
  • a conventional lubricant such as zinc stearate and additional carbon if desired, can be blended with the steel powder by suitable blending equipment.
  • the blended powder is then compacted into the desired shape by a compaction pressure generally above tons per square inch and preferably about tons per square inch.
  • the compacted powder is then sintered in a reducing atmosphere at a temperature in the range of 2,000 to 2,300 P. for a period of 10 minutes to 1 hour, depending on the composition and the final density desired.
  • the addition of the sulphur substantially improves the machineability of the sintered part.
  • the sulphur is believed to be present in the form of fine manganese sulphide dispersions which interrupt the steel matrix and cause the chips, during machining to break immediately ahead of the tool, resulting in a lower coefficient of friction between the tool and the work.
  • the chips formed during machining are generally short and bright with no discoloration due to excessive heating.
  • the machined surface is considerably smoother than the machined surface of a similar part without the addition of sulphur.
  • typical surface roughness measurements after identical machining operations show an arithmetic average surface roughness of 100 microinches on sintered metal prepared in accordance with the invention as compared to an average surface roughness of 250 microinches on identically processed sintered metal but without the addition of sulphur.
  • sulphur has been mixed with the steel particles prior to compacting and sintering in an attempt to increase the machineability of the sintered part.
  • the sulphur forms a film or a coating on each individual steel particle and this sulphur film seriously reduces the mechanical or physical properties of the sintered part.
  • the surface sulphur can cause serious damage to alloy mesh belts and furnace mufilers during sintering.
  • the sulphur is locked within the particles so that there is no layer or film of sulphur on the individual particles which can detract from the physical properties of the sintered part.
  • the sulphur provides some embrittlement for the steel, the fact that the sulphur is locked within the particles, enables the sintered part to have a substantially higher green density and green strength than sintered parts produced by conventional techniques in which the sulphur is merely mixed with the atomized particles.
  • a steel powder composition to be used in powder metallurgy processes comprising a plurality of steel particles with said steel having a carbon content less than 0.05% by weight and a manganese content less than 0.60% by weight, and a plurality of fine dispersions of sulphur distributed throughout the interior of said particles, said sulphur being present in the range of 0.08 to 0.25% by weight of the steel, said sulphur dispersions acting to improve the machineability of a metal part subsequently formed by compacting and sintering said particles.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture Of Metal Powder And Suspensions Thereof (AREA)
  • Powder Metallurgy (AREA)
US698738A 1968-01-18 1968-01-18 Method of making steel powder Expired - Lifetime US3528081A (en)

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US69873868A 1968-01-18 1968-01-18

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US (1) US3528081A (enrdf_load_stackoverflow)
DE (1) DE1902367A1 (enrdf_load_stackoverflow)
FR (1) FR2000381A1 (enrdf_load_stackoverflow)
GB (1) GB1252213A (enrdf_load_stackoverflow)
SE (1) SE351239B (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3725142A (en) * 1971-08-23 1973-04-03 Smith A Inland Inc Atomized steel powder having improved hardenability
US3798022A (en) * 1971-02-17 1974-03-19 Federal Mogul Corp Pre-alloyed nickel-free silicon-free minimal oxide low alloy iron powder
US3889350A (en) * 1971-03-29 1975-06-17 Ford Motor Co Method of producing a forged article from prealloyed water-atomized ferrous alloy powder
US3901661A (en) * 1972-04-06 1975-08-26 Toyo Kohan Co Ltd Prealloyed steel powder for formation of structural parts by powder forging and powder forged article for structural parts
US3942976A (en) * 1971-02-26 1976-03-09 Neo-Pro Corporation Metal recovery process
US3951035A (en) * 1971-12-01 1976-04-20 Nederlandsche Wapen-En Munitiefabriek De Kruithoorn N.V. Method of making dummy bullets
RU2130976C1 (ru) * 1998-05-15 1999-05-27 Сибирский государственный индустриальный университет Способ обработки расплава алюминиевых сплавов
CN103209791A (zh) * 2010-09-15 2013-07-17 Posco公司 铁系粉末的制备方法

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3798022A (en) * 1971-02-17 1974-03-19 Federal Mogul Corp Pre-alloyed nickel-free silicon-free minimal oxide low alloy iron powder
US3942976A (en) * 1971-02-26 1976-03-09 Neo-Pro Corporation Metal recovery process
US3889350A (en) * 1971-03-29 1975-06-17 Ford Motor Co Method of producing a forged article from prealloyed water-atomized ferrous alloy powder
US3725142A (en) * 1971-08-23 1973-04-03 Smith A Inland Inc Atomized steel powder having improved hardenability
US3951035A (en) * 1971-12-01 1976-04-20 Nederlandsche Wapen-En Munitiefabriek De Kruithoorn N.V. Method of making dummy bullets
US3901661A (en) * 1972-04-06 1975-08-26 Toyo Kohan Co Ltd Prealloyed steel powder for formation of structural parts by powder forging and powder forged article for structural parts
RU2130976C1 (ru) * 1998-05-15 1999-05-27 Сибирский государственный индустриальный университет Способ обработки расплава алюминиевых сплавов
CN103209791A (zh) * 2010-09-15 2013-07-17 Posco公司 铁系粉末的制备方法
US9156090B2 (en) 2010-09-15 2015-10-13 Posco Method of manufacturing iron-based powder
CN103209791B (zh) * 2010-09-15 2016-10-05 Posco公司 铁系粉末的制备方法

Also Published As

Publication number Publication date
DE1902367A1 (de) 1972-02-24
GB1252213A (enrdf_load_stackoverflow) 1971-11-03
SE351239B (enrdf_load_stackoverflow) 1972-11-20
FR2000381A1 (enrdf_load_stackoverflow) 1969-09-05

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