EP0354389B1 - Process for manufacturing sintered steel bodies, and bodies obtained thereby - Google Patents
Process for manufacturing sintered steel bodies, and bodies obtained thereby Download PDFInfo
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- EP0354389B1 EP0354389B1 EP89113211A EP89113211A EP0354389B1 EP 0354389 B1 EP0354389 B1 EP 0354389B1 EP 89113211 A EP89113211 A EP 89113211A EP 89113211 A EP89113211 A EP 89113211A EP 0354389 B1 EP0354389 B1 EP 0354389B1
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- sintered
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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%
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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
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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
- B22F3/26—Impregnating
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
Definitions
- the invention relates to a method for producing a molded part from sintered steel, sintered steel powder being compression-molded and sintered, after which the sintered part is austenitized by heating to temperatures above 800 ° C. and then rapidly cooled.
- the invention also relates to a molded part produced by the method.
- US Pat. No. 2,566,752 describes a method for producing an iron-containing metal part, namely a composite part.
- the composite part including copper infiltrated to achieve a higher strength For this purpose, it is proposed, after cooling, for example in oil or water, to reheat the metal to a temperature between 300 and 600 ° C. for a period of one to three hours in order to achieve infiltration of the desired constituents into the structure and thereby to increase the strength of the part.
- One of the essential features of the known molded parts made of sintered steel is the accuracy with which they can be produced. Diameter tolerances of high quality can be achieved. After the usual work sequence with a compression molding and a subsequent sintering, the sintered molding is calibrated for this. The high accuracy is achieved through the calibration process. Shaped parts that are not post-treated by calibration or another work process do not have such a high tolerance with sufficient repeatability.
- Sintered steels can achieve considerable yield strengths and tensile strength values, but their plastic deformability, which is measured, for example, as the elongation at break, and their toughness, which is measured, for example, as impact energy, are low.
- the strength limits the achievable accuracy of sintered molded parts. This is because post-sintering is economical, e.g. by calibration, can only be carried out if the strength of the material does not exceed 500 to a maximum of 600 N / mm2. Sintered steels with a significantly higher tensile strength can be easily produced, e.g. up to about 1200 N / mm2 tensile strength, because molded parts made from such materials can also be pressed and sintered, but they can no longer be economically calibrated to increase accuracy.
- a high strength of sintered steels can be achieved by alloying measures or by heat treatment, if necessary by a combination of both measures. Alloy-related measures have the disadvantage mentioned that they have high strength is achieved, but no economic calibration was possible to achieve the required accuracy.
- the present invention is therefore based on the object of providing a method for producing a sintered part and a sintered part produced thereafter, which has a high strength but at the same time also has good ductility, with the aim of achieving the highest possible dimensional accuracy.
- the temperature range and the conversion time depend on the steel composition.
- the first possibility is that the compression of the part to be sintered is chosen so high that a pore volume of less than 8% is achieved. With such a percentage, the pores are essentially no longer interconnected. This means that salt can then only settle into pores during the heat treatment which are open towards the surface of the sintered part. From there it can be easily washed out later.
- the second possibility is that the pores of the sintered part are at least partially filled with a filler which is resistant to the agents and chemicals used in a rapid cooling in a bath.
- metallic substances whose melting point is above the temperature of austenitizing but below the sintering temperature. This is e.g. generally the case for copper and corresponding copper alloys.
- non-metallic substances such as e.g. ceramic materials are used.
- ceramic materials e.g. Silicates or a mixture or a thin paste of talc and water glass possible.
- Numerous sintered steel powders commonly used in sintering molded parts are suitable for intermediate stage tempering. Both fully alloyed, i.e. atomize, as well as mixed alloy or alloyed powder. Pre-alloyed powders are obtained by melting iron with the desired alloy components, after which the melt is atomized into powder, which is then compression-molded in the usual way.
- Mixed alloy powder means that iron powder is mixed with alloy powder, after which the dry powder mixture is also compression molded.
- a middle way is the combination of both processes, which creates an alloyed powder for the subsequent compression molding.
- alloyed powders with, for example, 1.5 to 2% by weight of Ni, 0.3 to 0.6% by weight of Mo will be mixed with a corresponding residual amount of iron, and 0.3 to 1% by weight of graphite can also be added .
- copper can be tolerated as a shrinking alloy element in the usual framework.
- a molded part 1 is formed whose pores 2 are filled with copper.
- Tests with tensile tests have shown the following property values for the above example: Status R p N / mm2 R m N / mm2 A% State of the art only sintered 420..510 530..680 2.0..3.0 State of the art: hardened and tempered 900..1040 1050..1165 1.6..2.9 bainitized (intermediate stage tempered) 685..740 780..850 7.5.9.3
- field 3 with an alloy of FE-Cu-Ni-Mo-C having the highest tensile strength values with a relatively low elongation. If the same sintered alloy steel is hardened and tempered, field 4 is obtained. When copper is infiltrated at the same time during the sintering process and subsequent heat treatment as in field 4, field 5 with the highest tensile strength values is obtained, although the elongation is again relatively low.
- Field 6 shows the values for a sintered part produced by the method according to the invention. As can be seen from this, the tensile strength is significantly higher than that of sintered steels without any treatment and only insignificantly lower than with a hardened and tempered alloy steel. In contrast, however, the percentage elongation is several times better.
Description
Die Erfindung betrifft ein Verfahren zum Herstellen eines Formteiles aus Sinterstahl, wobei Sinterstahlpulver formgepreßt und gesintert wird, wonach das Sinterteil durch eine Erwärmung auf Temperaturen von über 800 °C austenitisiert und anschließend rasch abgekühlt wird. Ebenso betrifft die Erfindung ein nach dem Verfahren herstelltes Formteil.The invention relates to a method for producing a molded part from sintered steel, sintered steel powder being compression-molded and sintered, after which the sintered part is austenitized by heating to temperatures above 800 ° C. and then rapidly cooled. The invention also relates to a molded part produced by the method.
Aus der US-PS 2 566 752 ist ein Verfahren zur Herstellung eines eisenhaltigen Metallteiles, nämlich eines Verbundteiles beschrieben. In das Verbundteil wird u.a. Kupfer infiltriert, um eine höhere Festigkeit zu erreichen. Hierzu wird vorgeschlagen, nach einem Abkühlen, z.B. in Öl oder Wasser, das Metall wieder auf eine Temperatur zwischen 300 und 600 °C für eine Zeitdauer von ein bis drei Stunden zu erwärmen, um ein Infiltrieren der gewünschten Bestandteile in das Gefüge zu erreichen und dadurch die Festigkeit des Teiles zu erhöhen.US Pat. No. 2,566,752 describes a method for producing an iron-containing metal part, namely a composite part. In the composite part including copper infiltrated to achieve a higher strength. For this purpose, it is proposed, after cooling, for example in oil or water, to reheat the metal to a temperature between 300 and 600 ° C. for a period of one to three hours in order to achieve infiltration of the desired constituents into the structure and thereby to increase the strength of the part.
Eines der wesentlichen Merkmale der bekannten Formteile aus Sinterstahl ist deren Genauigkeit, mit der sie hergestellt werden können. Es sind Durchmessertoleranzen hoher Qualität erreichbar. Nach der üblichen Arbeitsfolge mit einem Formpressen und einem anschließenden Sintern wird das gesinterte Formteil hierzu kalibriert. Durch den Arbeitsgang des Kalibrierens wird die hohe Genauigkeit erreicht. Formteile, die nicht durch Kalibrieren oder einen anderen Arbeitsvorgang nachbehandelt werden, besitzen keine so hohe Toleranz mit ausreichender Wiederholbarkeit.One of the essential features of the known molded parts made of sintered steel is the accuracy with which they can be produced. Diameter tolerances of high quality can be achieved. After the usual work sequence with a compression molding and a subsequent sintering, the sintered molding is calibrated for this. The high accuracy is achieved through the calibration process. Shaped parts that are not post-treated by calibration or another work process do not have such a high tolerance with sufficient repeatability.
Ein weiteres Merkmal gesinterter Formteile ist die mehr oder weniger große Porigkeit ihrer Mikrostruktur. Diese Poren stellen innere Kerben dar und beeinflußen damit die Werkstoffeigenschaften erheblich. Mit Sinterstählen lassen sich damit zwar beachtliche Streckgrenzen- und Zugfestigkeitswerte erreichen, aber deren plastische Verformbarkeit, die z.B. als Bruchdehnung gemessen wird, und deren Zähigkeit, die z.B. als Schlagarbeit gemessen wird, sind gering.Another characteristic of sintered molded parts is the more or less large porosity of their microstructure. These pores represent and influence internal notches thus the material properties considerably. Sintered steels can achieve considerable yield strengths and tensile strength values, but their plastic deformability, which is measured, for example, as the elongation at break, and their toughness, which is measured, for example, as impact energy, are low.
Ebenso wie die Poren die Zähigkeit begrenzen, so begrenzt die Festigkeit die erreichbare Genauigkeit gesinterter Formteile. Dies liegt daran, daß eine Nacharbeit nach dem Sintern auf wirtschaftliche Weise, z.B. durch Kalibrieren, nur durchgeführt werden kann, wenn die Festigkeit des Werkstoffes 500 bis höchstens 600 N/mm² nicht übersteigt. Sinterstähle mit deutlich höherer Zugfestigkeit sind zwar ohne weiteres herstellbar, z.B. bis etwa 1200 N/mm² Zugfestigkeit, denn Formteile aus solchen Werkstoffen lassen sich zwar auch noch Pressen und Sintern, aber sie lassen sich nicht mehr auf wirtschaftliche Weise zur Erhöhung der Genauigkeit Kalibrieren.Just as the pores limit the toughness, the strength limits the achievable accuracy of sintered molded parts. This is because post-sintering is economical, e.g. by calibration, can only be carried out if the strength of the material does not exceed 500 to a maximum of 600 N / mm². Sintered steels with a significantly higher tensile strength can be easily produced, e.g. up to about 1200 N / mm² tensile strength, because molded parts made from such materials can also be pressed and sintered, but they can no longer be economically calibrated to increase accuracy.
Eine hohe Festigkeit an Sinterstählen läßt sich durch legierungstechnische Maßnahme oder durch eine Wärmebehandlung, ggf. durch eine Kombination beider Maßnahmen, erzielen. Legierungstechnische Maßnahmen haben den erwähnten Nachteil, daß damit zwar eine hohe Festigkeit erreicht wird, aber zur Erreichung einer erforderlichen Genauigkeit keine wirtschaftliche Kalibrierung möglich war.A high strength of sintered steels can be achieved by alloying measures or by heat treatment, if necessary by a combination of both measures. Alloy-related measures have the disadvantage mentioned that they have high strength is achieved, but no economic calibration was possible to achieve the required accuracy.
Aus diesem Grunde ist bereits versucht worden mit Legierungsbestandteilen in dem Sinterstahlpulver zu arbeiten, wobei nach dem Sintern eine Festigkeit von höchstens ca. 500 N/mm² erreicht worden ist. Anschließend konnten die auf diese Weise hergestellten Formteile kalibriert werden. Um eine höhere Festigkeit zu erhalten, wurde das Sinterteil danach gehärtet. Hierzu wurde es auf eine Temperatur zwischen 800 und 940 °C in Abhängigkeit von der Stahlzusammensetzung erwärmt, wobei eine Austenitisierung einsetzte. Durch ein rasches Abkühlen auf Raumtemperatur und ein anschließendes Anlassen (Wiedererwärmung) in bekannter Weise auf Temperaturen von max. ca. 500 °C wurde die gewünschte höhere Festigkeit erreicht, die auch bei über 1000 N/mm² liegen konnte. Ein derartig behandelter Sinterstahl war jedoch sehr spröde. Dies bedeutete, daß seine Verformbarkeit und Zähigkeit auf ein sehr niedriges Niveau abfielen. Es wurden Dehnungswerte von nur 1% bis 2% gemessen. Weiterhin traten dabei Maßveränderungen infolge von Verzug auf, die so groß waren, daß Toleranzen nur in einer geringen Qualität reproduziert werden konnten.For this reason, attempts have already been made to work with alloy components in the sintered steel powder, a strength of at most approx. 500 N /
Der vorliegenden Erfindung liegt daher die Aufgabe zugrunde ein Verfahren zum Herstellen eines Sinterteiles und ein danach hergestelltes Sinterteil zu schaffen, das eine hohe Festigkeit besitzt, gleichzeitig jedoch auch eine gute Dehnbarkeit aufweist, wobei darüberhinaus eine möglichst hohe Formgenauigkeit erreicht werden soll.The present invention is therefore based on the object of providing a method for producing a sintered part and a sintered part produced thereafter, which has a high strength but at the same time also has good ductility, with the aim of achieving the highest possible dimensional accuracy.
Erfindungsgemäß wird diese Aufgabe durch die Merkmale der kennzeichnenden Teile der Ansprüche 1, 2 und 13 gelöst. Bevorzugte Ausführungsformen sind in den abhängigen Ansprüchen offenbart.According to the invention, this object is achieved by the features of the characterizing parts of
Es wurde nämlich festgestellt, daß das durch eine rasche Abkühlung auf den genannten Temperaturbereich erzielte bainitische Gefüge eine hohe Festigkeit bei gleichzeitig guter Dehnbarkeit bzw. Zähigkeit besitzt. Im Vergleich zu einer normalen Härtung bzw. Vergütung können nahezu die gleichen Festigkeitswerte erreicht werden, wobei jedoch die Dehnung und Zähigkeit deutlich besser ist und gleichzeitig auch ein wesentlich geringerer maßlicher Verzug auftritt.It has been found that the bainitic structure achieved by rapid cooling to the temperature range mentioned has a high strength with good ductility or toughness. Compared to normal hardening or tempering, almost the same strength values can be achieved, but the elongation and toughness is significantly better and at the same time there is a much smaller dimensional distortion.
Es ist lediglich erforderlich, das zu behandelnde Gut so lange in dem angegebenen Temperaturbereich zu halten, bis das gesamte Gefüge in Bainit umgewandelt ist. Der Temperaturbereich und auch die Umwandlungszeit sind dabei abhängig von der Stahlzusammensetzung.It is only necessary to keep the material to be treated in the specified temperature range until the entire structure is converted into bainite. The temperature range and the conversion time depend on the steel composition.
Zwar ist der Arbeitsgang des Bainitisierens bereits bekannt, aber für Sinterstähle, war das Verfahren noch nicht angewendet worden. Dies liegt insbesondere daran, daß es bei einer einfachen Übertragung durch die vorhandene Porosität des Sinterteiles zu Problemen bei der nachfolgenden Härtung bzw. Abkühlung kommen würde. Zum Austenitisieren, d.h. zur Erwärmung des Sinterteiles, verwendet man ein Salzbad und anschließend für das isothermische Bainitisieren ein zweites Salzbad. Da Sinterstähle im allgemeinen sehr porös sind und die Poren häufig untereinander noch Verbindungen haben, besteht somit die Gefahr, daß bei der Salzschmelze oder bei Verwendung eines anderen Bades die hierfür verwendeten Chemikalien in das Innere der Sinterteile eindringen. Dadurch entstehen später sogenannte Ausblühungen, wodurch das Sinterteil sogar unbrauchbar werden kann.The process of bainitising is already known, but the method has not yet been used for sintered steels. This is due in particular to the fact that, in the case of a simple transfer, the porosity of the sintered part would cause problems during the subsequent hardening or cooling. To austenitize, ie to heat the sintered part, use a salt bath and then for isothermal bainitizing a second salt bath. Since sintered steels are generally very porous and the pores often still have connections to one another, there is a risk that the chemicals used for this will penetrate into the interior of the sintered parts when the salt is melted or when another bath is used. This later results in so-called efflorescence, which can even render the sintered part unusable.
Erfindungsgemäß werden deshalb zur Lösung dieses Problemes zwei Wege vorgeschlagen.According to the invention, two ways are therefore proposed to solve this problem.
Die erste Möglichkeit besteht darin, daß die Formpressung des zu sinternten Teiles so hoch gewählt wird, daß ein Porenvolumen von weniger als 8% erreicht wird. Bei einem derartigen Prozentsatz haben die Poren im wesentlichen untereinander keine Verbindung mehr. Dies bedeutet, daß Salz sich dann nur noch bei der Wärmebehandlung in Poren setzen kann, die zur Oberfläche des Sinterteiles hin offen sind. Von dort läßt es sich später leicht auswaschen.The first possibility is that the compression of the part to be sintered is chosen so high that a pore volume of less than 8% is achieved. With such a percentage, the pores are essentially no longer interconnected. This means that salt can then only settle into pores during the heat treatment which are open towards the surface of the sintered part. From there it can be easily washed out later.
Zur Anwendung dieses Verfahrens ist es erforderlich hoch verdichtbare Basispulver und/oder sehr hohe Pressdrücke zu verwenden. Dabei kann in vorteilhafter Weise auch eine stufenweise Behandlung mit einer Operationsfolge: Vorpressen - Vorsintern - Nachpressen - Fertigsintern - und ein anschließendes Bainitisieren durchgeführt werden.To use this method, it is necessary to use highly compactable and / or very high base powders To use pressures. In this case, a step-by-step treatment with an operation sequence: pre-pressing - pre-sintering - post-pressing - finished sintering - and a subsequent bainitization can advantageously be carried out.
Die zweite Möglichkeit besteht darin, daß die Poren des Sinterteiles wenigstens teilweise mit einem Füllstoff gefüllt werden, der gegen die bei einer raschen Abkühlung in einem Bad verwendeten Mittel und Chemikalien resistent ist.The second possibility is that the pores of the sintered part are at least partially filled with a filler which is resistant to the agents and chemicals used in a rapid cooling in a bath.
Für eine derartige Infiltration eignen sich z.B. metallische Stoffe, deren Schmelzpunkt über der Temperatur des Austenitisierens aber unter der Sintertemperatur liegt. Diese ist z.B. im allgemeinen für Kupfer und entsprechend Kupferlegierungen der Fall.For such infiltration, e.g. metallic substances whose melting point is above the temperature of austenitizing but below the sintering temperature. This is e.g. generally the case for copper and corresponding copper alloys.
Zur Füllung der Poren können jedoch auch nichtmetallische Stoffe, wie z.B. keramische Stoffe verwendet werden. So sind z.B. Silikate oder eine Mischung bzw. ein dünner Brei aus Talkum und Wasserglas möglich.However, non-metallic substances such as e.g. ceramic materials are used. For example, Silicates or a mixture or a thin paste of talc and water glass possible.
Im allgemeinen wird man jedoch eine Füllung der Poren mit metallischen Werkstoffen vorziehen, da ja bei der Wärmebehandlung die Abkühlung von der hohen Austenittemperatur auf die Temperatur der Bainitumwandlung sehr rasch erfolgen muß. Dies wird durch Metall oder andere Werkstoffe mit einer guten Wärmeleitfähigkeit als Infiltrate gewährleistet.In general, however, it is preferable to fill the pores with metallic materials, since in the heat treatment the cooling from the high austenite temperature takes place to the temperature of the bainite transformation must be done very quickly. This is ensured by metal or other materials with good thermal conductivity as infiltrates.
Zum Zwischenstufenvergüten sind zahlreiche in der sintertechnischen Formteilefertigung gängigen Sinterstahlpulver geeignet. Möglich sind sowohl fertiglegierte, d.h. verdüste, ebenso wie mischlegierte oder anlegierte Pulver. Fertiglegierte Pulver erhält man durch Erschmelzen von Eisen mit den gewünschten Legierungsbestandteilen, wonach die Schmelze zu Pulver verdüst wird, das anschließend in üblicher Weise formgepreßt wird. Mischlegiertes Pulver bedeutet, daß man Eisenpulver mit Legierungspulver zusammenmischt, wonach die trockene Pulvermischung ebenfalls formgepreßt wird. Ein Mittelweg ist die Kombination aus beiden Verfahren, womit ein anlegiertes Pulver für die nachfolgende Formpressung entsteht.Numerous sintered steel powders commonly used in sintering molded parts are suitable for intermediate stage tempering. Both fully alloyed, i.e. atomize, as well as mixed alloy or alloyed powder. Pre-alloyed powders are obtained by melting iron with the desired alloy components, after which the melt is atomized into powder, which is then compression-molded in the usual way. Mixed alloy powder means that iron powder is mixed with alloy powder, after which the dry powder mixture is also compression molded. A middle way is the combination of both processes, which creates an alloyed powder for the subsequent compression molding.
Im allgemeinen wird man fertiglegierte Pulver mit z.B. 1,5 bis 2 Gew.% Ni, 0,3 bis 0,6 Gew.% Mo einer entsprechenden Restmenge Eisen zumischen, wobei zusätzlich noch 0,3 bis 1 Gew.% Graphit beigegeben werden kann. Ggf. kann Kupfer im üblichen Rahmen als schwundausgleichendes Legierungselement toleriert werden.In general, alloyed powders with, for example, 1.5 to 2% by weight of Ni, 0.3 to 0.6% by weight of Mo will be mixed with a corresponding residual amount of iron, and 0.3 to 1% by weight of graphite can also be added . Possibly. copper can be tolerated as a shrinking alloy element in the usual framework.
Nachfolgend sind nähere Einzelheiten der Erfindung beispielsweise anhand der Zeichnung beschrieben.Further details of the invention are described below, for example with reference to the drawing.
Es zeigt:
- Fig. 1:
- ausschnittsweise Schnitt durch ein Sinterteil;
- Fig. 2:
- die Beziehung zwischen Zugfestigkeit und Dehnung für verschiedene Legierungssysteme und Wärmebehndlungen.
- Fig. 1:
- Sectional section through a sintered part;
- Fig. 2:
- the relationship between tensile strength and elongation for different alloy systems and heat treatments.
Aus einem fertiglegierten Pulver mit folgender Zusammensetzung:
1,8 Gew.% Ni
0,5 Gew.% Mo
1,5 Gew.% Cu
Rest Fe
dem als Zusätze
ca. 0,4 Gew.% Graphitpulver
ca. 1% Mikrowachs als Schmiermittel
zugemischt werden, wird ein Formteil so gepreßt, daß seine Dichte ca. 7,1 g/cm² beträgt. Dies entspricht damit einem Porenvolumen von 9,9%. Anschließend wird bei ca. 1230 °C für 40 Minuten unter Schutzgas gesintert. Während des Sintervorganges wird auf das Formteil so viel Kupferblech aufgelegt, daß sein Gewicht dem Porenvolumen entspricht, welches im vorliegenden Falle rund 10% des Teilegewichtes beträgt. Bei der Sintertemperatur schmilzt das Kupfer und kann damit in die Poren infiltrieren.From a finished alloy powder with the following composition:
1.8 wt% Ni
0.5% by weight Mo
1.5% by weight of Cu
Rest of Fe
that as additives
approx. 0.4% by weight graphite powder
approx. 1% micro wax as lubricant
admixed, a molded part is pressed so that its density is about 7.1 g / cm². This corresponds to a pore volume of 9.9%. Then sintered under protective gas at approx. 1230 ° C for 40 minutes. During the sintering process, so much copper sheet is placed on the molded part that its weight corresponds to the pore volume, which in the present case is around 10% of the part weight. At the sintering temperature, the copper melts and can thus infiltrate into the pores.
Nach dem Sintern wird das Formteil kalibriert und anschließend folgender Wärmebehandlung unterzogen.
- 1. Austenitisieren bei 870 °C, 15 Minuten im Salzbad
- 2.
Innerhalb von 2 Minuten abkühlen auf 345 °C durch Tauchen in entsprechend erwärmtes Salzbad - 3. Halten auf 320 °C 45 Minuten im Salzbad
- 4. beliebige Abkühlung.
- 1. Austenitize at 870 ° C, 15 minutes in a salt bath
- 2. Cool to 345 ° C within 2 minutes by immersing in a suitably heated salt bath
- 3. Hold at 320 ° C for 45 minutes in a salt bath
- 4. any cooling.
Auf diese Weise entsteht gemäß Fig. 1 ein Formteil 1 dessen Poren 2 mit Kupfer gefüllt sind.1, a molded part 1 is formed whose
Versuche mit Zerreißproben haben für das vorstehend aufgeführte Beispiel folgende Eigenschaftswerte ergeben:
Dabei bedeutet:
- Rp =
- Proportionalitätsgrenze
- Rm =
- Festigkeit
- A% =
- Dehnung.
- R p =
- Proportionality limit
- R m =
- strength
- A% =
- Strain.
Wie ersichtlich, liegt zwar gegenüber einem gehärteten und angelassenen Sinterteil 1 eine etwas geringere Proportionalität und Festigkeit vor, aber die Dehnbarkeit ist um ein mehrfaches besser. Gegenüber nur gesinterten Formteilen ist neben der höheren Proportionalität und Festigkeit auch die Dehnbarkeit deutlich besser.As can be seen, there is a somewhat lower proportionality and strength compared to a hardened and tempered sintered part 1, but the extensibility is several times better. Compared to only sintered molded parts, in addition to the higher proportionality and strength, the ductility is significantly better.
In der Fig. 2 sind Werte für verschiedene Sinterstahlsorten bezüglich der Zugfestigkeit über der Dehnung aufgetragen.In FIG. 2, values for different types of sintered steel are plotted with regard to tensile strength over elongation.
Dabei sind im unteren Bereich der Zugfestigkeit mehrere Felder mit verschiedenen bekannten Legierungszusammensetzungen dargestellt, wobei das Feld 3 mit einer Legierung aus FE-Cu-Ni-Mo-C die höchsten Zugfestigkeitswerte bei einer allerdings relativ geringen Dehnung aufweist. Wird der gleiche gesinterte Legierungstahl gehärtet und angelassen, so erhält man das Feld 4. Bei einer gleichzeitigen Infiltrierung von Kupfer während des Sintervorganges und einer anschließend gleichen Wärmebehandlung wie bei Feld 4 erhält man das Feld 5 mit den höchsten Zugfestigkeitswerten, wobei allerdings die Dehnung wiederum relativ gering ist. In dem Feld 6 sind die Werte für ein nach dem erfindungsgemäßen Verfahren hergestelltes Sinterteil ersichtlich. Wie daraus zu entnehmen ist, ist die Zugfestigkeit deutlich höher als die von Sinterstählen ohne jede Behandlung und nur unwesentlich niedriger als bei einem gehärteten und angelassenen Legierungsstahl. Im Unterschied dazu ist jedoch die prozentuale Dehnung um ein mehrfaches besser.Several fields with different known alloy compositions are shown in the lower area of tensile strength, field 3 with an alloy of FE-Cu-Ni-Mo-C having the highest tensile strength values with a relatively low elongation. If the same sintered alloy steel is hardened and tempered,
Aus dem Vergleich zwischen den Feldern 4 und 5 ist ersichtlich, daß zwar durch Infiltrieren mit Kupfer die Zugfestigkeit nochmals gesteigert werden kann, aber die Dehnung bleibt in dem gleichen geringen Umfange, wenn sie nicht sogar etwas niedriger ausfällt.It can be seen from the comparison between
Messungen der Durchmesser an ringähnlichen Teilen (außen und innen) die aus einer Pulvermischung entsprechend dem o.a. Ausführungsbeispiel gepreßt und wie beschrieben bainitisiert worden sind, haben ergeben, daß die Toleranz vor und nach der Wärmebehandlung auf der gleichen Qualitätsstufe lag. Bekannte Sinterteile, die durch Härten und nachfolgendes Anlassen vergütet worden sind, erfuhren bei gleichen Teilen dagegen durch die Wärmebehandlung eine deutliche Toleranzvergröberung. Auch für porige Stähle zeigt es sich damit, daß der Maßverzug durch das erfindungsgemäße Bainitisieren deutlich kleiner ist als der durch eine konventionelle Vergütung hervorgerufene.Measurements of the diameter of ring-like parts (outside and inside), which were pressed from a powder mixture in accordance with the above embodiment and bainitized as described, showed that the tolerance before and after the heat treatment was at the same quality level. Known sintered parts, tempered by hardening and subsequent tempering on the other hand, with the same parts, the heat treatment caused a clear increase in tolerance. For porous steels it also shows that the dimensional distortion due to the bainitization according to the invention is significantly smaller than that caused by conventional tempering.
Claims (20)
- Process for manufacturing sintered steel bodies, in which sintered steel powder is compression moulded and sintered, after which the sintered body is austenitised by heating to temperatures in excess of 800°C and then is cooled rapidly, characterised in that the compression moulding of the body to be sintered is so great that a pore volume of less than 8 % is obtained, and that, after the austenitic heat treatment, the sintered body is cooled to a temperature of 280 to 450°C and is kept in this temperature range for between 5 and 60 minutes, a bainitic microstructure thereby being obtained.
- Process for manufacturing sintered steel bodies, in which sintered steel powder is compression moulded and sintered, after which the sintered body is austenitised by heating to temperatures in excess of 800°C and then is cooled rapidly, characterised in that the pores of the sintered body are at least partially filled with a filler which is resistant to the compositions and chemicals used during rapid cooling in a bath, and that, after the austenitic heat treatment, the sintered body is cooled to a temperature of 280 to 450°C and is kept in this temperature range for between 5 and 60 minutes, a bainitic microstructure thereby being obtained.
- Process according to claim 1 or claim 2, characterised in that cooling is effected in a temperature range of 320 to 360°C.
- Process according to claim 1, 2 or 3, characterised in that the sintered body is kept in the temperature range for between 20 and 40 minutes.
- Process according to one of claims 1 - 4, characterised in that the austenitic heat treatment is carried out at 800 to 900°C for a period of 10 to 60 minutes.
- Process according to claim 5, characterised in that the austenitic heat treatment is carried out at 800 to 900°C for a period of 15 to 20 minutes.
- Process according to claim 1, characterised in that the body to be sintered is rough-pressed, then presintered and subsequently repressed and finish sintered.
- Process according to claim 2, characterised in that a metallic substance the melting point of which is situated above the austenitising temperature but below the sintering temperature is used as a filler.
- Process according to claim 8, characterised in that copper or a copper alloy is used as a filler.
- Process according to claim 2, characterised in that a ceramic substance is used as a filler.
- Process according to claim 10, characterised in that silicate, such as talc and/or water glass, is used as a filler.
- Process according to one of claims 1 - 11, characterised in that, as a sintered material, in addition to iron, 1.5 to 2 % by weight Ni and 0.3 to 0.6 % by weight Mo are used as an alloying powder, 0.3 to 1.0 % by weight graphite being added.
- Sintered steel body, characterised in that it has a pore volume of less than 8 % and that its microstructure consists of bainite.
- Sintered steel body according to claim 13, characterised in that the pores of the sintered body are at least partially filled with a filler which is resistant to the compositions and chemicals used during rapid cooling in a bath and that its microstructure consists of bainite.
- Body according to claim 14, characterised in that its pore spaces are at least partially filled with a non-ferrous metal the melting point of which is between 920 and 1230°C.
- Body according to claim 15, characterised in that the non-ferrous metal is copper or a copper alloy.
- Body according to claim 14, characterised in that its pore spaces are at least partially filled with a non-metallic substance.
- Body according to claim 17, characterised in that the non-metallic substance is a ceramic substance, such as talc and/or water glass.
- Body according to claim 13 or claim 14, characterised in that its specific weight is between 6.8 g/cm³ and 7.4 g/cm³.
- Body according to claim 19, characterised in that the specific weight is approximately 7.3 g/cm³.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3825463 | 1988-07-27 | ||
| DE3825463A DE3825463A1 (en) | 1988-07-27 | 1988-07-27 | METHOD FOR PRODUCING A MOLDING PART FROM SINTERMETAL AND MOLDING PART MADE THEREOF |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0354389A1 EP0354389A1 (en) | 1990-02-14 |
| EP0354389B1 true EP0354389B1 (en) | 1994-05-04 |
Family
ID=6359640
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP89113211A Expired - Lifetime EP0354389B1 (en) | 1988-07-27 | 1989-07-19 | Process for manufacturing sintered steel bodies, and bodies obtained thereby |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0354389B1 (en) |
| DE (2) | DE3825463A1 (en) |
| ES (1) | ES2054943T3 (en) |
| PT (1) | PT91283B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19521941C1 (en) * | 1995-06-07 | 1996-10-02 | Mannesmann Ag | Mfg. sintered air-hardenable alloy steel component |
| DE19524251C1 (en) * | 1995-07-04 | 1997-02-13 | Supervis Ets | Process for producing a sintered molded part |
| JP4001450B2 (en) * | 2000-05-02 | 2007-10-31 | 日立粉末冶金株式会社 | Valve seat for internal combustion engine and manufacturing method thereof |
| SE0201824D0 (en) * | 2002-06-14 | 2002-06-14 | Hoeganaes Ab | Pre-alloyed iron based powder |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2566752A (en) * | 1948-10-14 | 1951-09-04 | American Electro Metal Corp | Method of producing a ferrous metal article infiltrated with a cuprous infiltrant |
| US4002471A (en) * | 1973-09-24 | 1977-01-11 | Federal-Mogul Corporation | Method of making a through-hardened scale-free forged powdered metal article without heat treatment after forging |
| JPS50115108A (en) * | 1974-02-21 | 1975-09-09 | ||
| US4343661A (en) * | 1978-11-15 | 1982-08-10 | Caterpillar Tractor Co. | Method of making a low temperature bainite steel alloy gear |
| DE3142359A1 (en) * | 1981-10-26 | 1983-05-05 | Horst Dipl.-Phys. Dr. 6000 Frankfurt Mühlberger | Process and device for heat-treating workpieces |
-
1988
- 1988-07-27 DE DE3825463A patent/DE3825463A1/en not_active Withdrawn
-
1989
- 1989-07-19 EP EP89113211A patent/EP0354389B1/en not_active Expired - Lifetime
- 1989-07-19 ES ES89113211T patent/ES2054943T3/en not_active Expired - Lifetime
- 1989-07-19 DE DE58907598T patent/DE58907598D1/en not_active Expired - Fee Related
- 1989-07-26 PT PT91283A patent/PT91283B/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| PT91283A (en) | 1990-02-08 |
| PT91283B (en) | 1995-03-01 |
| DE3825463A1 (en) | 1990-02-01 |
| DE58907598D1 (en) | 1994-06-09 |
| EP0354389A1 (en) | 1990-02-14 |
| ES2054943T3 (en) | 1994-08-16 |
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