EP2252420B1 - Method for producing a sintered, iron-based workpiece - Google Patents

Method for producing a sintered, iron-based workpiece Download PDF

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Publication number
EP2252420B1
EP2252420B1 EP09718461A EP09718461A EP2252420B1 EP 2252420 B1 EP2252420 B1 EP 2252420B1 EP 09718461 A EP09718461 A EP 09718461A EP 09718461 A EP09718461 A EP 09718461A EP 2252420 B1 EP2252420 B1 EP 2252420B1
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EP
European Patent Office
Prior art keywords
surface layer
sintered
boron
carbon
blank
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EP09718461A
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German (de)
French (fr)
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EP2252420A1 (en
Inventor
Peter Orth
Gerold MSc. STETINA
Herbert Danninger
Christian Gierl
Peter Hofbauer
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Miba Sinter Austria GmbH
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Miba Sinter Austria GmbH
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    • 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
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/24—After-treatment of workpieces or articles
    • 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
    • B22F2998/00—Supplementary information concerning processes or compositions relating to powder metallurgy
    • B22F2998/10—Processes characterised by the sequence of their steps
    • 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
    • B22F2999/00—Aspects linked to processes or compositions used in powder metallurgy

Definitions

  • the invention relates to a method for producing an iron-based sintered workpiece, wherein a molding is pressed from a sintered powder and sintered into a blank before the blank is compacted in the region of a surface layer.
  • the invention is therefore based on the object, a method of the type described for producing a sintered iron-based workpiece in such a way that despite a waiver of expensive pusher tools limited to a surface layer compression of the workpiece can be guaranteed, with a comparatively low manufacturing tolerance ,
  • the invention achieves the stated object in that the sintered blank is enriched in the surface area to be compacted with carbon and / or boron and resintered above the solidus temperature of the enriched surface layer.
  • the invention makes use of the finding that the sintering behavior of pressed moldings from an iron-based sintering powder depends on the content of certain storage elements, in particular the content of carbon and boron. While no pronounced densification of the sintered material can be observed below a critical carbon or boron content during sintering, the compression of a sintered material increases accordingly high carbon and boron levels during sintering. With a carbon and boron content over the respectively critical areas, a liquid phase is formed which spontaneously forms from the respective mixed crystals of the iron with carbon and boron when the solidus temperature is exceeded and allows a largely nonporous sintered body.
  • the liquid phase remains in the resintering Carbon or boron enriched surface layer, with the result that only this surface layer of the compaction is subjected by the liquid phase sintering, while in the remaining parts of the blank, only a normal solid phase sintering occurs.
  • the enrichment of the surface layer with carbon and / or boron can be carried out in a conventional manner. For example, carbon enrichment in the surface layer is possible by means of gas carburizing or low pressure carburizing.
  • the presintered blank can be placed in a manner known per se in powder or pasty boron or subjected to plasma processing. It depends only on the accumulation of the intercalators carbon and boron, but not on the method used for it.
  • the enrichment of the intercalation elements carbon and boron in a surface layer of the blank required for liquid-phase sintering entails the risk of embrittlement of the surface layer. To counteract this risk, it is advisable to carry out the resintering required for compaction isothermally, in particular to reduce the carbon content of the surface layer by Abdiffundieren the carbon in the interior of the blank and thereby avoid the excretion of grain boundary carbides.
  • the carbon content in the surface layer to be compacted should be greater than 1 mass%. However, this means overcooling of the surface layer to a depth of typically 1 to 1.5 mm in view of the later use of the workpiece. If the isothermal sintering is carried out above the solidus temperature until the carbon content has dropped below 1% by mass, the risk of embrittlement of the surface layer due to excess carbon is largely eliminated.
  • the grain coarsening associated with the resintering above the solidus temperature can be counteracted by normalizing the resintered blank in a manner known per se.
  • boron enrichment is recommended to the extent of 0.01 to 0.6 mass%.
  • the danger of embrittlement can be avoided by carrying out the resintering under a deboring atmosphere.
  • a hydrogen atmosphere is suitable, because in such a hydrogen atmosphere, the boron, after it has unfolded its effect on the spontaneous formation of a liquid phase, is partially removed again from the surface layer of the blank and does not interfere further.
  • the resintering can also be carried out in a non-deboronating atmosphere, such as argon, or in a vacuum, resintering in a nitrogen atmosphere is not recommended. Namely boron nitride is formed in a nitrogen atmosphere, whereby the liquid sintering phase activating effect of the boron is lost.
  • a prealloyed iron powder with 1.5 mass% molybdenum is mixed with 0.3 mass% graphite and 0.8 mass% ⁇ thylenbisstearoylamid as a lubricant and pressed at 600 MPa to a molding dewaxing at 800 ° C over a period of 30 minutes and at the same time subjected to a solid phase sintering becomes.
  • the sintered parison is carburized in a conventional gas carburizing furnace to set a carbon content of 1.2 mass% in the surface layer. Thereafter, the blank is sintered in a walking beam oven under a nitrogen atmosphere for 45 minutes at 1320 ° C, wherein the heating rate to this sintering temperature 15 K / min.
  • the blank is cooled at an average of 10 K / min to 400 ° C and then subjected to normalizing at 900 ° C, which annealing temperature is maintained for 10 minutes. Thereafter, the workpiece is cooled to room temperature in a nitrogen atmosphere at a cooling rate of 10 K / min.
  • the porosity of the workpiece was measured in the core at 9 to 11% and in the area of the compacted surface layer to a depth of 0.3 mm at less than 2%.
  • a prealloyed iron powder having 3 mass% chromium and 0.5 mass% molybdenum is mixed with 0.35 mass% graphite and 0.6 mass% of a lubricant before a molding is pressed at a molding pressure of 400 MPa.
  • the molding is dewaxed in a belt furnace and sintered at 1120 ° C. for 30 minutes.
  • the sintered parison is carburized in a low pressure carbonitriding furnace at 900 ° C, using acetylene as the carbon support, which is introduced into the furnace in a pulsed manner.
  • the carburized in a surface layer blank is heated in a vacuum oven at a heating rate of 10 K / min to a post-sintering temperature of 1300 ° C and held at this temperature for 60 min, then first under vacuum conditions and then from 1100 ° C in a nitrogen atmosphere with Cooling rate of 10 K / min to 300 ° C to be cooled.
  • the blank is heated again to 900 ° C and then quenched with nitrogen.
  • the thus hardened workpiece is tempered at 180 ° C.
  • the residual porosity was in a compacted surface layer up to in a depth of 0.5 mm less than 2% and showed a hardness greater than 500 HV3.
  • the core porosity was measured at 13%.
  • An iron powder prealloyed with 1.5% by mass of chromium and 0.2% by mass of molybdenum is mixed with 0.2% by mass of graphite and 0.6% by mass of lubricant and pressed at 700 MPa into a shaped article.
  • the sintering and dewaxing of this molding is carried out at 800 ° C.
  • the molding is placed in a powder mixture of ferroboron, ferromanganese and aluminum oxide and sintered in an oven for 30 min at 1000 ° C in a hydrogen atmosphere simultaneously and borated.
  • the sintered blank is sintered in a sintering furnace for 1 h isothermally at 1250 ° C in flowing hydrogen.
  • the compacted surface layer had a thickness of 0.5 to 0.7 mm and showed a residual porosity of less than 1%, while the core porosity was 9%.

Abstract

The invention relates to a method for producing a sintered, iron-based workpiece, wherein a formation is pressed from a sinter powder and sintered into a blank, before the blank is consolidated in the region of a surface layer. In order to enable the surface to be consolidated without a presser tool, it is proposed that the sintered blank be enriched with carbon and/or boron in the surface regions, which are to be consolidated, and resintered above the solidus temperature of the enriched surface layer.

Description

Technisches GebietTechnical area

Die Erfindung bezieht sich auf ein Verfahren zum Herstellen eines gesinterten Werkstückes auf Eisenbasis, wobei ein Formling aus einem Sinterpulver gepresst und zu einem Rohling gesintert wird, bevor der Rohling im Bereich einer Oberflächenschicht verdichtet wird.The invention relates to a method for producing an iron-based sintered workpiece, wherein a molding is pressed from a sintered powder and sintered into a blank before the blank is compacted in the region of a surface layer.

Stand der TechnikState of the art

Um eine höhere Dauerbiegefestigkeit im Bereich der Zahnfüße und eine höhere Verschleißfestigkeit im Bereich der Zahnflanken bei pulvermetallurgisch hergestellten Zahnrädern zu erreichen, ist es bekannt ( EP 0 552 272 B1 , AT 406 836B WO 2008/013 581 ), die gesinterten Pulvermetallrohlinge der Zahnräder im Flanken- und im Fußbereich der Zähne zu verdichten, sodass eine weitgehend porenfreie Oberflächenschicht erhalten wird, die im Eingriffsbereich des Zahnrades eine erhebliche Steigerung der zulässigen Belastbarkeit mit sich bringt. Die Verdichtung der Oberflächenschicht im Eingriffsbereich des Zahnrades erfolgt über ein Drückerwerkzeug in Form wenigstens eines Zahnrades, das entweder eine in die Verzahnung des Pulvermetallrohlings eingreifende Außenverzahnung ( EP 0 552 B1 ) oder eine Innenverzahnung ( AT 406 836 B ) aufweist, mit deren Hilfe die Gleitgeschwindigkeit zwischen den Zahnflanken des Pulvermetallrohlings und des Drückerwerkzeuges verringert werden kann. Diese Drückerwerkzeuge bedingen jedoch im Allgemeinen einen erheblichen Konstruktionsaufwand und sind einem entsprechenden Verschleiß unterworfen. Außerdem besteht unabhängig von der Art des jeweils eingesetzten Drückerwerkzeuges die Gefahr einer über die Oberflächenverdichtung hinausgehenden Verformung des Werkstückes.In order to achieve a higher bending fatigue strength in the area of the tooth roots and a higher wear resistance in the region of the tooth flanks in powder-metallurgically produced toothed wheels, it is known ( EP 0 552 272 B1 . AT 406 836B WO 2008/013581 ), the sintered powder metal blanks of the gears in the flank and foot of the teeth to densify, so that a largely non-porous surface layer is obtained, which brings in the engagement region of the gear a significant increase in the allowable load capacity. The compaction of the surface layer in the engagement region of the toothed wheel takes place via a pusher tool in the form of at least one toothed wheel, which either has an external toothing (FIG. 3) engaging in the toothing of the powder metal blank (FIG. EP 0 552 B1 ) or an internal toothing ( AT 406 836 B ), with the aid of which the sliding speed between the tooth flanks of the powder metal blank and the pusher tool can be reduced. However, these pusher tools generally require considerable design effort and are subject to wear. In addition, there is a risk, regardless of the type of pusher tool used in each case a beyond the surface compression deformation of the workpiece.

Durch ein Sintern mit einer weitgehend flüssigen Phase kann zwar die Porosität der Rohlinge wesentlich verringert und damit eine Festigkeitssteigerung erzielt werden, doch ist mit einem solchen Flüssigphasensintern ein erhebliches Schwinden des Sinterwerkstoffes verbunden. Abgesehen davon, dass sich das Schwindverhalten nachteilig auf die Fertigungstoleranzen des Werkstückes auswirkt, ist es häufig aus Gewichtsgründen erwünscht, nur die entsprechend belasteten Werkstückbereiche durch ein Verdichten einer Oberflächenschicht zu verstärken.By sintering with a substantially liquid phase, although the porosity of the blanks can be substantially reduced and thus an increase in strength can be achieved, but with such a liquid phase sintering a considerable shrinkage of the sintered material is connected. Apart from the fact that the shrinkage behavior adversely affects the manufacturing tolerances of the workpiece, it is often desirable for weight reasons, only to reinforce the correspondingly loaded workpiece areas by compacting a surface layer.

Darstellung der ErfindungPresentation of the invention

Der Erfindung liegt somit die Aufgabe zugrunde, ein Verfahren der eingangs geschilderten Art zum Herstellen eines gesinterten Werkstückes auf Eisenbasis so auszugestalten, dass trotz eines Verzichts auf aufwändige Drückerwerkzeuge eine auf eine Oberflächenschicht begrenzte Verdichtung des Werkstückes gewährleistet werden kann, und zwar bei einer vergleichsweise geringen Fertigungstoleranz.The invention is therefore based on the object, a method of the type described for producing a sintered iron-based workpiece in such a way that despite a waiver of expensive pusher tools limited to a surface layer compression of the workpiece can be guaranteed, with a comparatively low manufacturing tolerance ,

Die Erfindung löst die gestellte Aufgabe dadurch, dass der gesinterte Rohling im zu verdichtenden Oberflächenbereich mit Kohlenstoff und/oder Bor angereichert und über der Solidustemperatur der angereicherten Oberflächenschicht nachgesintert wird.The invention achieves the stated object in that the sintered blank is enriched in the surface area to be compacted with carbon and / or boron and resintered above the solidus temperature of the enriched surface layer.

Die Erfindung nützt die Erkenntnis, dass das Sinterverhalten von gepressten Formlingen aus einem Sinterpulver auf Eisenbasis vom Gehalt bestimmter Einlagerungselemente, insbesondere von Gehalt an Kohlenstoff und Bor, abhängt. Während unterhalb eines kritischen Kohlenstoff- oder Borgehalts beim Sintern keine ausgeprägte Verdichtung des Sinterwerkstoffes beobachtet werden kann, nimmt die Verdichtung eines Sinterwerkstoffes mit entsprechend hohen Kohlenstoff- und Borgehalten beim Sintern stark zu. Mit einem Kohlenstoff- und Borgehalt über den jeweils kritischen Bereichen bildet sich nämlich eine flüssige Phase aus, die beim Überschreiten der Solidustemperatur spontan aus den jeweiligen Mischkristallen des Eisens mit Kohlenstoff und Bor entsteht und einen weitgehend porenfreien Sinterkörper ermöglicht. Da erfindungsgmäß lediglich eine Oberflächenschicht des gesinterten Rohlings mit Kohlenstoff und/oder Bor in einem die diesbezüglich kritischen Werte übersteigenden Ausmaß angereichert und der Rohling einer Nachsinterung bei einer Temperatur über der Solidustemperatur der angereicherten Oberflächenschicht unterworfen wird, bleibt die flüssige Phase bei der Nachsinterung auf die mit Kohlenstoff bzw. Bor angereicherte Oberflächenschicht mit der Folge beschränkt, dass lediglich diese Oberflächenschicht der Verdichtung durch das Flüssigphasensintern unterworfen wird, während in den übrigen Teilen des Rohlings nur ein normales Festphasensintern auftritt. Die Anreicherung der Oberflächenschicht mit Kohlenstoff und/oder Bor kann in herkömmlicher Weise vorgenommen werden. So ist beispielsweise eine Kohlenstoffanreicherung in der Oberflächenschicht mit Hilfe einer Gasaufkohlung oder einer Niederdruckaufkohlung möglich. Zur Boranreicherung kann der vorgesinterte Rohling in an sich bekannter Weise in pulver- oder pastenförmig vorliegendes Bor eingelegt oder einem Plasmaborieren unterworfen werden. Es kommt ja lediglich auf die Anreicherung der Einlagerungselemente Kohlenstoff und Bor, nicht aber auf die dafür eingesetzten Verfahren an.The invention makes use of the finding that the sintering behavior of pressed moldings from an iron-based sintering powder depends on the content of certain storage elements, in particular the content of carbon and boron. While no pronounced densification of the sintered material can be observed below a critical carbon or boron content during sintering, the compression of a sintered material increases accordingly high carbon and boron levels during sintering. With a carbon and boron content over the respectively critical areas, a liquid phase is formed which spontaneously forms from the respective mixed crystals of the iron with carbon and boron when the solidus temperature is exceeded and allows a largely nonporous sintered body. Since, according to the invention, only one surface layer of the sintered blank is enriched with carbon and / or boron in excess of the critical values in this regard, and the blank is subjected to resintering at a temperature above the solidus temperature of the enriched surface layer, the liquid phase remains in the resintering Carbon or boron enriched surface layer, with the result that only this surface layer of the compaction is subjected by the liquid phase sintering, while in the remaining parts of the blank, only a normal solid phase sintering occurs. The enrichment of the surface layer with carbon and / or boron can be carried out in a conventional manner. For example, carbon enrichment in the surface layer is possible by means of gas carburizing or low pressure carburizing. For boron enrichment, the presintered blank can be placed in a manner known per se in powder or pasty boron or subjected to plasma processing. It depends only on the accumulation of the intercalators carbon and boron, but not on the method used for it.

Die für das Flüssigphasernsintern erforderliche Anreicherung der Einlagerungselemente Kohlenstoff und Bor in einer Oberflächenschicht des Rohlings birgt die Gefahr einer Versprödung der Oberflächenschicht mit sich. Um dieser Gefahr zu begegnen, empfiehlt es sich, die für das Verdichten erforderliche Nachsinterung isotherm durchzuführen, um insbesondere den Kohlenstoffgehalt der Oberflächenschicht durch ein Abdiffundieren des Kohlenstoffes in das Innere des Rohlings zu senken und dadurch die Ausscheidung von Korngrenzcarbiden zu vermeiden.The enrichment of the intercalation elements carbon and boron in a surface layer of the blank required for liquid-phase sintering entails the risk of embrittlement of the surface layer. To counteract this risk, it is advisable to carry out the resintering required for compaction isothermally, in particular to reduce the carbon content of the surface layer by Abdiffundieren the carbon in the interior of the blank and thereby avoid the excretion of grain boundary carbides.

Damit das spontane Entstehen der flüssigen Phase aus den Eisen-Kohlenstoff-Mischkristallen sichergestellt wird, soll der Kohlenstoffgehalt in der zu verdichtenden Oberflächenschicht größer als 1 Massen% gewählt werden. Dies bedeutet aber im Hinblick auf den späteren Werkstückeinsatz eine Überkohlung der Oberflächenschicht bis in eine Tiefe von typischerweise 1 bis 1,5 mm. Wird die isotherme Sinterung über der Solidustemperatur solange durchgeführt, bis der Kohlenstoffgehalt unter 1 Massen% gesunken ist, so ist die Gefahr einer Versprödung der Oberflächenschicht durch überschüssigen Kohlenstoff weitgehend gebannt. Der mit der Nachsinterung über der Solidustemperatur einhergehenden Kornvergröberung kann durch ein Normalglühen des nachgesinterten Rohlings in an sich bekannter Weise begegnet werden.To ensure the spontaneous formation of the liquid phase from the iron-carbon mixed crystals, the carbon content in the surface layer to be compacted should be greater than 1 mass%. However, this means overcooling of the surface layer to a depth of typically 1 to 1.5 mm in view of the later use of the workpiece. If the isothermal sintering is carried out above the solidus temperature until the carbon content has dropped below 1% by mass, the risk of embrittlement of the surface layer due to excess carbon is largely eliminated. The grain coarsening associated with the resintering above the solidus temperature can be counteracted by normalizing the resintered blank in a manner known per se.

Wird Bor zum Verdichten der Oberflächenschicht eingesetzt, so empfiehlt sich eine Boranreicherung in einem Ausmaß von 0,01 bis 0,6 Massen%. Dabei kann die Versprödungsgefahr dadurch vermieden werden, dass die Nachsinterung unter einer entborierenden Atmosphäre durchgeführt wird. Hierfür eignet sich insbesondere eine Wasserstoffatmosphäre, weil in einer solchen Wasserstoffatmosphäre das Bor, nachdem es seine Wirkung auf die spontane Entstehung einer flüssigen Phase entfaltet hat, aus der Oberflächenschicht des Rohlings zum Teil wieder entfernt wird und nicht weiter stört. Während die Nachsinterung auch in einer nicht entborierenden Atmosphäre, wie Argon, oder in Vakuum durchgeführt werden kann, ist eine Nachsinterung in einer Stickstoffatmosphäre nicht zu empfehlen. In einer Stickstoffatmosphäre bildet sich nämlich Bornitrid, wodurch die die flüssige Sinterphase aktivierende Wirkung des Bors verloren geht.If boron is used to densify the surface layer, boron enrichment is recommended to the extent of 0.01 to 0.6 mass%. In this case, the danger of embrittlement can be avoided by carrying out the resintering under a deboring atmosphere. For this purpose, in particular, a hydrogen atmosphere is suitable, because in such a hydrogen atmosphere, the boron, after it has unfolded its effect on the spontaneous formation of a liquid phase, is partially removed again from the surface layer of the blank and does not interfere further. While the resintering can also be carried out in a non-deboronating atmosphere, such as argon, or in a vacuum, resintering in a nitrogen atmosphere is not recommended. Namely boron nitride is formed in a nitrogen atmosphere, whereby the liquid sintering phase activating effect of the boron is lost.

Ausführungsbeispiel 1:Embodiment 1

Ein vorlegiertes Eisenpulver mit 1,5 Massen% Molybdän wird mit 0,3 Massen% Graphit und 0,8 Massen% Äthylenbisstearoylamid als Gleitmittel versetzt und mit 600 MPa zu einem Formling gepresst, der bei 800° C über eine Zeitspanne von 30 Minuten entwachst und zugleich einer Festphasensinterung unterworfen wird. Der gesinterte Rohling wird in einem herkömmlichen Gasaufkohlofen aufgekohlt, wobei ein Kohlenstoffgehalt von 1,2 Massen% in der Oberflächenschicht eingestellt wird. Danach wird der Rohling in einem Hubbalkenofen unter einer Stickstoffatmosphäre 45 min bei 1320° C gesintert, wobei die Aufheizrate auf diese Sintertemperatur 15 K/min beträgt. Nach der isothermen Sinterung wird der Rohling mit durchschnittlich 10 K/min auf 400° C abgekühlt und anschließend einem Normalglühen bei 900° C unterworfen, welche Glühtemperatur für 10 Minuten aufrechterhalten wird. Danach wird das Werkstück in einer Stickstoffatmosphäre mit einer Kühlrate von 10 K/min auf Raumtemperatur abgekühlt. Die Porosität des Werkstückes wurde im Kern mit 9 bis 11 % und im Bereich der verdichteten Oberflächenschicht bis in eine Tiefe von 0,3 mm mit weniger als 2 % gemessen.A prealloyed iron powder with 1.5 mass% molybdenum is mixed with 0.3 mass% graphite and 0.8 mass% Äthylenbisstearoylamid as a lubricant and pressed at 600 MPa to a molding dewaxing at 800 ° C over a period of 30 minutes and at the same time subjected to a solid phase sintering becomes. The sintered parison is carburized in a conventional gas carburizing furnace to set a carbon content of 1.2 mass% in the surface layer. Thereafter, the blank is sintered in a walking beam oven under a nitrogen atmosphere for 45 minutes at 1320 ° C, wherein the heating rate to this sintering temperature 15 K / min. After isothermal sintering, the blank is cooled at an average of 10 K / min to 400 ° C and then subjected to normalizing at 900 ° C, which annealing temperature is maintained for 10 minutes. Thereafter, the workpiece is cooled to room temperature in a nitrogen atmosphere at a cooling rate of 10 K / min. The porosity of the workpiece was measured in the core at 9 to 11% and in the area of the compacted surface layer to a depth of 0.3 mm at less than 2%.

Ausführungsbeispiel 2:Embodiment 2:

Ein vorlegiertes Eisenpulver mit 3 Massen% Chrom und 0,5 Massen% Molybdän wird mit 0,35 Massen% Graphit und 0,6 Massen% eines Gleitmittels gemischt, bevor ein Formling mit einem Pressdruck von 400 MPa gepresst wird. Der Formling wird in einem Bandofen entwachst und bei 1120° C 30 min gesintert. Zum Aufkohlen wird der gesinterte Rohling in einem Niederdruck-Carbonitrierofen bei 900° C aufgekohlt, wobei als Kohlenstoffträger Acetylen verwendet wird, dass pulsweise in den Ofen eingebracht wird. Der in einer Oberflächenschicht aufgekohlte Rohling wird in einem Vakuumofen mit einer Heizrate von 10 K/min auf eine Nachsintertemperatur von 1300° C erwärmt und auf dieser Temperatur für 60 min gehalten, um dann zunächst unter Vakuumbedingungen und dann ab 1100° C in einer Stickstoffatmosphäre mit einer Kühlrate von 10 K/min auf 300° C abgekühlt zu werden. Zum Normalglühen wird der Rohling wieder auf 900° C erwärmt und anschließend mit Stickstoff abgeschreckt. Das auf diese Weise gehärtete Werkstück wird bei 180° C angelassen. Die Restporosität betrug in einer verdichteten Oberflächenschicht bis in eine Tiefe von 0,5 mm weniger als 2 % und zeigte eine Härte größer als 500 HV3. Die Kernporosität wurde mit 13 % gemessen.A prealloyed iron powder having 3 mass% chromium and 0.5 mass% molybdenum is mixed with 0.35 mass% graphite and 0.6 mass% of a lubricant before a molding is pressed at a molding pressure of 400 MPa. The molding is dewaxed in a belt furnace and sintered at 1120 ° C. for 30 minutes. For carburizing, the sintered parison is carburized in a low pressure carbonitriding furnace at 900 ° C, using acetylene as the carbon support, which is introduced into the furnace in a pulsed manner. The carburized in a surface layer blank is heated in a vacuum oven at a heating rate of 10 K / min to a post-sintering temperature of 1300 ° C and held at this temperature for 60 min, then first under vacuum conditions and then from 1100 ° C in a nitrogen atmosphere with Cooling rate of 10 K / min to 300 ° C to be cooled. For normalizing the blank is heated again to 900 ° C and then quenched with nitrogen. The thus hardened workpiece is tempered at 180 ° C. The residual porosity was in a compacted surface layer up to in a depth of 0.5 mm less than 2% and showed a hardness greater than 500 HV3. The core porosity was measured at 13%.

Ausführungsbeispiel 3:Embodiment 3

Ein mit 1,5 Massen% Chrom und 0,2 Massen% Molybdeän vorlegiertes Eisenpulver wird mit 0,2 Massen% Graphit und 0,6 Massen% Gleitmittel gemischt und mit 700 MPa zu einem Formling gepresst. Die Sinterung und Entwachsung dieses Formlings erfolgt bei 800° C. Anschließend wird der Formling in ein Pulvergemisch aus Ferrobor, Ferromangan und Aluminiumoxid eingelegt und in einem Ofen 30 min bei 1000° C in einer Wasserstoffatmosphäre gleichzeitig gesintert und boriert. Im Anschluss daran wird der gesinterte Rohling in einem Sinterofen während 1 h isotherm bei 1250° C in strömendem Wasserstoff nachgesintert. Die verdichtete Oberflächenschicht wies eine Dicke von 0,5 bis 0.7 mm auf und zeigte eine Restporosität kleiner als 1 %, während die Kernporosität 9 % betrug.An iron powder prealloyed with 1.5% by mass of chromium and 0.2% by mass of molybdenum is mixed with 0.2% by mass of graphite and 0.6% by mass of lubricant and pressed at 700 MPa into a shaped article. The sintering and dewaxing of this molding is carried out at 800 ° C. Subsequently, the molding is placed in a powder mixture of ferroboron, ferromanganese and aluminum oxide and sintered in an oven for 30 min at 1000 ° C in a hydrogen atmosphere simultaneously and borated. Subsequently, the sintered blank is sintered in a sintering furnace for 1 h isothermally at 1250 ° C in flowing hydrogen. The compacted surface layer had a thickness of 0.5 to 0.7 mm and showed a residual porosity of less than 1%, while the core porosity was 9%.

Claims (7)

  1. Method for producing a sintered iron-based work piece, wherein a blank is pressed from a sintering powder and sintered to form a billet, before the billet is compacted in the region of a surface layer, characterised in that, in the surface region to be compacted, the sintered billet is enriched with carbon and/or boron to a degree exceeding the critical values for the formation of a spontaneous liquid phase when the solidus temperature is exceeded, and is resintered above the solidus temperature of the enriched surface layer.
  2. Method as claimed in claim 1, characterised in that the billet is resintered isothermally.
  3. Method as claimed in claim 1 or 2, characterised in that in the case of enrichment of the surface layer with carbon, the carbon content in the surface layer to be compacted is greater than 1% by mass.
  4. Method as claimed in claim 3, characterised in that the isothermal sintering is carried out above the solidus temperature until the carbon content has fallen below 1 % by mass.
  5. Method as claimed in any one of claims 1 to 4, characterised in that the resintered billet is subjected to normalization.
  6. Method as claimed in claim 1 or 2, characterised in that in the case of enrichment of the surface layer with boron, the boron content in the surface layer to be compacted is between 0.01 and 0.6% by mass.
  7. Method as claimed in claim 1, 2 or 6, characterised in that in the case of enrichment of the surface layer with boron, the billet is resintered in a deboronizing atmosphere, preferably in a hydrogen atmosphere.
EP09718461A 2008-03-06 2009-03-05 Method for producing a sintered, iron-based workpiece Not-in-force EP2252420B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AT0036408A AT506444B1 (en) 2008-03-06 2008-03-06 METHOD FOR PRODUCING A SINTERED WORKPIECE ON IRON BASE
PCT/AT2009/000089 WO2009108981A1 (en) 2008-03-06 2009-03-05 Method for producing a sintered, iron-based workpiece

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EP2252420A1 EP2252420A1 (en) 2010-11-24
EP2252420B1 true EP2252420B1 (en) 2011-09-07

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5613180A (en) * 1994-09-30 1997-03-18 Keystone Investment Corporation High density ferrous power metal alloy
US5729822A (en) * 1996-05-24 1998-03-17 Stackpole Limited Gears
DE102005027055A1 (en) * 2005-06-10 2006-12-14 Gkn Sinter Metals Gmbh Process to manufacture teeth on a gear cog by cutting preform and sintering processes
US7905018B2 (en) * 2006-03-29 2011-03-15 Hitachi Powdered Metals Co., Ltd. Production method for sintered gear
US7722803B2 (en) * 2006-07-27 2010-05-25 Pmg Indiana Corp. High carbon surface densified sintered steel products and method of production therefor

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ATE523275T1 (en) 2011-09-15
WO2009108981A1 (en) 2009-09-11
EP2252420A1 (en) 2010-11-24
AT506444B1 (en) 2010-01-15
AT506444A1 (en) 2009-09-15

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