EP0049531B1 - Method of case-hardening metallic pieces - Google Patents

Method of case-hardening metallic pieces Download PDF

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Publication number
EP0049531B1
EP0049531B1 EP81108035A EP81108035A EP0049531B1 EP 0049531 B1 EP0049531 B1 EP 0049531B1 EP 81108035 A EP81108035 A EP 81108035A EP 81108035 A EP81108035 A EP 81108035A EP 0049531 B1 EP0049531 B1 EP 0049531B1
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Prior art keywords
gas
pressure fluctuations
furnace
carbon
components
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EP81108035A
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German (de)
French (fr)
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EP0049531A1 (en
Inventor
Karlheinz Längerich
Rüdiger Dr. Conrad
Wolfgang Dr. Danzer
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Linde GmbH
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Linde GmbH
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C23C8/22—Carburising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases

Definitions

  • the invention relates to a method for case hardening metallic workpieces, in which they are exposed in a furnace at high temperatures to the action of a carbon-containing gas atmosphere in which pressure fluctuations are generated.
  • Case hardening is a process for the heat treatment of metals in the presence of a carbon-containing or nitrogen-containing gas mixture, in which the surface layer of a metal workpiece is thermochemically treated with carbon and, if necessary, with nitrogen (carburizing or carbonitriding).
  • the heat treatment changes the chemical composition of the workpiece by diffusing carbon or nitrogen in or out.
  • the transport of the gaseous carburizing agent to the workpiece can be the rate-determining step of the carburizing process in the case of rapidly carburizing gas atmospheres.
  • the transport of the gaseous carburizing agent to the workpiece can be the rate-determining step of the carburizing process in the case of rapidly carburizing gas atmospheres.
  • GB-A-527 081 discloses a method for carburizing.
  • a gas mixture is prepared outside a furnace, compressed to a pressure above ambient pressure and then expanded into the furnace interior. The pressure increase inside the furnace is reduced by leaks in the furnace.
  • a process for case hardening is known from DE-B-1 041 067, in which pressure fluctuations are generated in the gas atmosphere within a furnace.
  • Hardening technology notices Vol. 35 (1980) No. 5, pages 230 to 237, disclose the use of a treatment gas for case hardening, which is composed of gases containing carbon, nitrogen and oxygen. From hardening technology communications, Vol. 35 (1980) No. 6, pages 284 to 288, it is known for thermochemical treatment to regulate the composition of the furnace atmosphere by measuring the residual methane content or the oxygen partial pressure.
  • the carburizing agent for example methane
  • the carburizing agent is added in two or three time intervals, which are interrupted by breaks in which no carburizing agent is added and the diffusion of the carbon or nitrogen into the edge area of the metallic workpiece takes place. In relation to the time period of the heat treatment, these intervals last relatively long (a few minutes up to approx. 1 hour).
  • the invention is therefore based on the object of specifying a method of the type described in the introduction, in which a uniform surface quality of all treated metallic workpieces is achieved by the heat treatment.
  • This object is achieved in that the gas atmosphere is formed from at least two components and the pressure fluctuations are generated by pulsating the addition of at least two components with different amplitudes and frequencies of the pressure fluctuations of the individual gas components in the furnace.
  • gas movement is forced by constant pressure changes during the heat treatment process of the entire gas atmosphere and thus also in the vicinity of geometrically unfavorable metal parts. Due to the pressure changes, a largely homogeneous gas atmosphere is established in all furnace areas.
  • the carburizing agent or the carbonitriding agent is therefore transported to the workpiece uniformly and sufficiently quickly at all points on the workpiece to be treated, so that the carbon potential has almost the same value at all points on the workpiece surface during the carburizing process. Insufficient carburization of disadvantaged workpiece surfaces or excessive carburization of favored workpiece surfaces is therefore avoided.
  • edge zone properties of the workpieces treated by the method according to the invention therefore improve since it is not necessary to add oxygen to remove the soot deposits.
  • the method according to the invention also shortens the entire carburizing process, since a large carbon potential gradient is achieved between the workpiece surface and the workpiece core and this potential gradient also acts as a driving diffusion force.
  • the gas mixture is composed of an inert carrier gas, a carbon- and nitrogen-containing gas and a oxygen-containing gas formed.
  • the pressure fluctuations are generated by pulsating admixing of two gas components to the third gas component or by pulsating mixing of all gas components.
  • the pressure fluctuations of the inert carrier gas can be dimensioned such that a constant gas movement which is dependent on the furnace size, among other things, is brought about within the furnace, while the pressure fluctuations of the carbon-containing or nitrogen-containing gas are primarily aimed at the carbon or carbide required for case hardening. Provide sufficient nitrogen.
  • the period of the pressure fluctuations is advantageously shorter compared to the duration of the heat treatment.
  • the method according to the invention is particularly useful when the furnace atmosphere outside the furnace is formed from two or more components, which are stored individually and mixed under excess pressure and input into the furnace.
  • each individual gas component can be mixed with the other components in a pulsating manner.
  • only one shut-off device is required, which can be operated automatically if necessary.
  • a hydrocarbon with more than one carbon atom is advantageously used as the carbon-containing gas in the process according to the invention.
  • Such hydrocarbons become unstable at the temperatures prevailing in the furnace and break down into several gaseous radicals. Because of the constant furnace volume, the decay results in a pressure increase, which is higher the more radicals are formed. This effect is superimposed on the pressure fluctuations caused by the pulsating addition and amplifies these fluctuations.
  • the frequency of the pressure fluctuations is set as a function of the methane and / or hydrogen and / or soot content in the furnace atmosphere.
  • the method according to the invention not only achieves a faster carburization but also an improved carburization - in particular at geometrically unfavorable points.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Threshing Machine Elements (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Making Paper Articles (AREA)

Description

Die Erfindung betrifft ein Verfahren zum Einsatzhärten metallischer Werkstücke, bei dem diese in einem Ofen bei hohen Temperaturen der Einwirkung einer kohlenstoffhaltigen Gasatmosphäre ausgesetzt werden, in der Druckschwankungen erzeugt werden.The invention relates to a method for case hardening metallic workpieces, in which they are exposed in a furnace at high temperatures to the action of a carbon-containing gas atmosphere in which pressure fluctuations are generated.

Das Einsatzhärten ist ein Verfahren zur Wärmebehandlung von Metallen in Gegenwart eines kohlenstoffhaltigen bzw. stickstoffhaltigen Gasgemisches, bei dem die Randschicht eines metallischen Werkstückes mit Kohlenstoff und gegebenenfalls mit Stickstoff thermochemisch behandelt wird (Aufkohlen bzw. Carbonitrieren). Durch die Wärmebehandlung wird die chemische Zusammensetzung des Werkstückes durch Ein- oder Ausdiffundieren von Kohlenstoff bzw. Stickstoff geändert.Case hardening is a process for the heat treatment of metals in the presence of a carbon-containing or nitrogen-containing gas mixture, in which the surface layer of a metal workpiece is thermochemically treated with carbon and, if necessary, with nitrogen (carburizing or carbonitriding). The heat treatment changes the chemical composition of the workpiece by diffusing carbon or nitrogen in or out.

Der Transport des gasförmigen Aufkohlungsmittels zum Werkstück zum Beispiel kann bei schnellaufkohlenden Gasatmosphären der geschwindigkeitsbestimmende Schritt des Aufkohlungsvorganges sein. Besonders bei dichtgepackten Chargen, bei Schüttgut oder bei geometrisch ungünstigen Teilen ist dann ein ausreichend schneller Transport an benachteiligte Werkstückoberflächen nicht mehr gegeben, was zu ungenügender Aufkohlung (z. B. bei Zahnrädern im Zahngrund) bzw. zu Weichfleckigkeit führt.The transport of the gaseous carburizing agent to the workpiece, for example, can be the rate-determining step of the carburizing process in the case of rapidly carburizing gas atmospheres. Especially with tightly packed batches, with bulk goods or with geometrically unfavorable parts, there is no longer a sufficiently fast transport to disadvantaged workpiece surfaces, which leads to insufficient carburization (e.g. with gear wheels in the tooth base) or soft spots.

Bisher versuchte man durch optimale Lüfterkonstruktionen bzw. durch Erhöhung des Gasdurchsatzes diese ungünstigen Aufkohlungsergebnisse zu vermeiden.So far, attempts have been made to avoid these unfavorable carburizing results by means of optimal fan designs or by increasing the gas throughput.

Durch die GB-A-527 081 ist ein Verfahren zum Aufkohlen bekannt. Dabei wird außerhalb eines Ofens ein Gasgemisch vorbereitet, auf einen Druck über Umgebungsdruck verdichtet und nachfolgend in den Ofeninnenraum entspannt. Über Undichtigkeiten im Ofen wird der Druckanstieg innerhalb des Ofens abgebaut.GB-A-527 081 discloses a method for carburizing. A gas mixture is prepared outside a furnace, compressed to a pressure above ambient pressure and then expanded into the furnace interior. The pressure increase inside the furnace is reduced by leaks in the furnace.

Durch die DE-B-1 041 067 ist ein Verfahren zum Einsatzhärten bekannt, bei dem in der Gasatmosphäre innerhalb eines Ofens Druckschwankungen erzeugt werden. Durch Härtereitechnische Mitteilungen, Vol. 35 (1980) Nr. 5, Seite 230 bis 237, ist die Verwendung eines Behandlungsgases zum Einsatzhärten bekannt, das sich aus kohlenstoff-, stickstoff- und sauerstoffhaltigen Gasen zusammensetzt. Durch Härtereitechnische Mitteilungen, Vol. 35 (1980) Nr. 6, Seiten 284 bis 288 ist es für eine thermochemische Behandlung bekannt, die Zusammensetzung der Ofenatmosphäre über die Messung des Restmethangehaltes oder des Sauerstoffpartialdurcks zu regeln.A process for case hardening is known from DE-B-1 041 067, in which pressure fluctuations are generated in the gas atmosphere within a furnace. Hardening technology notices, Vol. 35 (1980) No. 5, pages 230 to 237, disclose the use of a treatment gas for case hardening, which is composed of gases containing carbon, nitrogen and oxygen. From hardening technology communications, Vol. 35 (1980) No. 6, pages 284 to 288, it is known for thermochemical treatment to regulate the composition of the furnace atmosphere by measuring the residual methane content or the oxygen partial pressure.

Außerdem ist es bekannt, das Kohlungsmittel, beispielsweise Methan, intervallweise der zur Wärmebehandlung dienenden Gasatmosphäre zuzugeben. Bei diesem « Intervallkohlen wird das Kohlungsmittel in zwei oder drei Zeitintervallen zugegeben, die von Pausen unterbrochen sind, in denen kein kohlungsmittel zugeführt wird und die Diffusion des Kohlenstoffs bzw. Stickstoffs in den Randbereich des metallischen Werkstückes stattfindet. Bezögen auf die Zeitspanne der Wärmebehandlung dauern diese Intervalle relativ lang (einige Minuten bis zu ca. 1 Stunde).It is also known to add the carburizing agent, for example methane, at intervals to the gas atmosphere used for the heat treatment. With this “interval carbon”, the carburizing agent is added in two or three time intervals, which are interrupted by breaks in which no carburizing agent is added and the diffusion of the carbon or nitrogen into the edge area of the metallic workpiece takes place. In relation to the time period of the heat treatment, these intervals last relatively long (a few minutes up to approx. 1 hour).

Mit den bekannten Maßnahmen läßt sich jedoch nicht sicher ausschließen, daß sich in der Charge Toträume ausbilden, in denen das Kohlungsmittel nur langsam ausgetauscht wird.With the known measures, however, it cannot be reliably ruled out that dead spaces form in the batch in which the carbonizing agent is exchanged only slowly.

Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren der eingangs geschilderten Art anzugeben, bei dem durch die Wärmebehandlung eine gleichmäßige Oberflächenqualität aller behandelten metallischen Werkstücke erzielt wird. Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß die Gasatmosphäre aus wenigstens zwei Komponenten gebildet wird und die Druckschwankungen durch pulsierendes Zugeben von wenigstens zwei Komponenten mit unterschiedlichen Amplituden und Frequenzen der Druckschwankungen der einzelnen Gaskomponenten in den Ofen erzeugt werden.The invention is therefore based on the object of specifying a method of the type described in the introduction, in which a uniform surface quality of all treated metallic workpieces is achieved by the heat treatment. This object is achieved in that the gas atmosphere is formed from at least two components and the pressure fluctuations are generated by pulsating the addition of at least two components with different amplitudes and frequencies of the pressure fluctuations of the individual gas components in the furnace.

Erfindungsgemäß wird durch ständige Druckwechsel während des Wärmebehandlungsprozesses der gesamten Gasatmosphäre und somit auch in der Nähe geometrisch ungünstiger Metallteile eine Gasbewegung erzwungen. Aufgrund der Druckwechsel stellt sich in allen Ofenbereichen eine weitgehend homogene Gasatmosphäre ein. Der Transport des Aufkohlungsmittels bzw. des Carbonitrierungsmittels zum Werkstück erfolgt daher an alle Stellen des zu behandelnden Werkstückes gleichmäßig und genügend schnell, so daß das Kohlenstoffpotential während des Aufkohlungsvorganges an allen Stellen der Werkstückoberfläche nahezu den gleichen Wert hat. Eine ungenügende Aufkohlung benachteiligter Werkstückoberflächen bzw. ein zu starkes Aufkohlen begünstigter Werkstückoberflächen wird daher vermieden. Da über alle Oberflächenbereiche eine gleichmäßige Aufkohlung bzw. Carbonitrierung erfolgt, muß eine Rußabscheidung an geometrisch bevorzugten Stellen nicht mehr in Kauf genommen werden, wenn an ungünstigen Stellen eine bestimmte Aufkohlungs- bzw. Aufstickungstiefe erzielt werden soll. Die Randzonenbeschaffenheit der nach dem erfindungsgemäßen Verfahren behandelten Werkstücke verbessert sich demzufolge, da es sich erübrigt, diesen Sauerstoff zur Beseitigung der Rußablagerungen zuzuführen.According to the invention, gas movement is forced by constant pressure changes during the heat treatment process of the entire gas atmosphere and thus also in the vicinity of geometrically unfavorable metal parts. Due to the pressure changes, a largely homogeneous gas atmosphere is established in all furnace areas. The carburizing agent or the carbonitriding agent is therefore transported to the workpiece uniformly and sufficiently quickly at all points on the workpiece to be treated, so that the carbon potential has almost the same value at all points on the workpiece surface during the carburizing process. Insufficient carburization of disadvantaged workpiece surfaces or excessive carburization of favored workpiece surfaces is therefore avoided. Since a uniform carburization or carbonitriding takes place over all surface areas, soot deposition at geometrically preferred locations no longer has to be accepted if a certain carburization or nitriding depth is to be achieved at unfavorable locations. The edge zone properties of the workpieces treated by the method according to the invention therefore improve since it is not necessary to add oxygen to remove the soot deposits.

Neben einer verbesserten Aufkohlung bewirkt das erfindungsgemäße Verfahren auch eine Verkürzung des gesamten Aufkohlungsprozesses, da ein großes Kohlenstoffpotentialgefälle zwischen Werkstückoberfläche und Werkstückkern erreicht wird und dieses Potentialgefälle zusätzlich als treibende Diffusionskraft wirkt.In addition to an improved carburization, the method according to the invention also shortens the entire carburizing process, since a large carbon potential gradient is achieved between the workpiece surface and the workpiece core and this potential gradient also acts as a driving diffusion force.

Erfindungsgemäß ist es möglich, Amplitude und Frequenz der Druckschwankungen der einzelnen Gaskomponenten unterschiedlich zu wählen. In einer vorteilhaften Ausgestaltung der Erfindung wird das Gasgemisch aus einem inerten Trägergas, einem kohlenstoff- und stickstoffhaltigen Gas und einem sauerstoffhaltigen Gas gebildet. Dabei werden die Druckschwankungen durch pulsierendes Zumischen von zwei Gaskomponenten zur dritten Gaskomponente bzw. durch pulsierendes Vermischen aller Gaskomponenten erzeugt. Beispielsweise können die Druckschwankungen des inerten Trägergases so bemessen sein, daß innerhalb des Ofens eine unter anderem von der Ofengröße abhängige stete Gasbewegung bewirkt wird, während die Druckschwankungen des kohlenstoff- bzw. stickstoffhaltigen Gases primär darauf ausgerichtet werden, den für die Einsatzhärtung erforderlichen Kohlenstoff bzw. Stickstoff in ausreichender Menge bereitzustellen.According to the invention, it is possible to choose the amplitude and frequency of the pressure fluctuations of the individual gas components differently. In an advantageous embodiment of the invention, the gas mixture is composed of an inert carrier gas, a carbon- and nitrogen-containing gas and a oxygen-containing gas formed. The pressure fluctuations are generated by pulsating admixing of two gas components to the third gas component or by pulsating mixing of all gas components. For example, the pressure fluctuations of the inert carrier gas can be dimensioned such that a constant gas movement which is dependent on the furnace size, among other things, is brought about within the furnace, while the pressure fluctuations of the carbon-containing or nitrogen-containing gas are primarily aimed at the carbon or carbide required for case hardening. Provide sufficient nitrogen.

In einer Ausgestaltung der Erfindung ist die Periodendauer der Druckschwankungen vorteilhafterweise im Vergleich zur Dauer der Wärmebehandlung kürzer.In one embodiment of the invention, the period of the pressure fluctuations is advantageously shorter compared to the duration of the heat treatment.

Das erfindungsgemäße Verfahren bietet sich insbesondere dann an, wenn die Ofenatmosphäre außerhalb des Ofens aus zwei oder mehreren Komponenten gebildet wird, die einzeln gespeichert und unter Überdruck gemischt und in den Ofen eingegeben werden. Durch einfaches Öffnen und Schließen der jeweiligen Versorgungsleitungen kann jede einzelne Gaskomponente pulsierend den übrigen Komponenten zugemischt werden. Zu diesem Zweck ist nur je ein Absperrorgan erforderlich, das gegebenenfalls automatisch bedient werden kann.The method according to the invention is particularly useful when the furnace atmosphere outside the furnace is formed from two or more components, which are stored individually and mixed under excess pressure and input into the furnace. By simply opening and closing the respective supply lines, each individual gas component can be mixed with the other components in a pulsating manner. For this purpose, only one shut-off device is required, which can be operated automatically if necessary.

Mit Vorteil wird beim erfindungsgemäßen Verfahren als kohlenstoffhaltiges Gas ein Kohlenwasserstoff mit mehr als einem Kohlenstoffatom eingesetzt. Derartige Kohlenwasserstoffe werden bei den im Ofen herrschenden Temperaturen instabil und zerfallen in mehrere gasförmige Radikale. Wegen des konstanten Ofenvolumens ist mit dem Zerfall einer Druckerhöhung verbunden, die umso höher ist, je mehr Radikale gebildet werden. Dieser Effekt überlagert sich mit den durch die pulsierende Zugabe hervorgerufenen Druckschwankungen und verstärkt diese Schwankungen.A hydrocarbon with more than one carbon atom is advantageously used as the carbon-containing gas in the process according to the invention. Such hydrocarbons become unstable at the temperatures prevailing in the furnace and break down into several gaseous radicals. Because of the constant furnace volume, the decay results in a pressure increase, which is higher the more radicals are formed. This effect is superimposed on the pressure fluctuations caused by the pulsating addition and amplifies these fluctuations.

Nach einem Merkmal des erfindungsgemäßen Verfahrens wird die Frequenz der Druckschwankungen in Abhängigkeit vom Methan-, und/oder Wasserstoff- und/oder Rußgehalt der Ofenatmosphäre eingestellt.According to a feature of the method according to the invention, the frequency of the pressure fluctuations is set as a function of the methane and / or hydrogen and / or soot content in the furnace atmosphere.

Im folgenden sollen anhand einer Skizze zwei Versuche beschrieben werden, deren Ergebnis die Verbesserungen, die durch das erfindungsgemäße Verfahren (Versuch 1) gegenüber dem herkömmlichen Verfahren (Versuch 2) erreicht werden, deutlich aufzeigen.Two experiments are described below with the aid of a sketch, the results of which clearly show the improvements which are achieved by the method according to the invention (experiment 1) compared to the conventional method (experiment 2).

Bei beiden Versuchen wurden folgende Parameter nicht geändert :

Figure imgb0001
The following parameters were not changed in either experiment:
Figure imgb0001

Variiert wurde nur die Art der Propanzugabe :

  • Bei Versuch 1 :
    • Propanzugabe 1 m3 in 2 Stunden pulsierend 15 sec. Propanzugabe (Ofenüberdruck 90 mbar) 60 sec. keine Propanzugabe (Druck 30 mbar)
  • Bei Versuch 2 :
    • Propanzugabe 1 m3 in 2 Stunden gleichmäßig keine Druckschwankungen (Druck 40 mbar)
Only the type of propane was varied:
  • In experiment 1:
    • Propane addition 1 m 3 pulsating in 2 hours 15 sec. Propane addition (furnace pressure 90 mbar) 60 sec. No propane addition (pressure 30 mbar)
  • In experiment 2:
    • Propane addition 1 m 3 in 2 hours evenly no pressure fluctuations (pressure 40 mbar)

Die unterschiedliche Aufkohlungswirkung der erfindungsgemäßen und der herkömmlichen Verfahrensweise wird deutlich, wenn man den Härteverlauf von Doppelstirnrädern (Werkstoff 16 MCr5) betrachtet, die in Versuch 1 nach dem erfindungsgemäßen Verfahren bzw. in Versuch 2 nach der herkömmlichen Verfahrensweise einsatzgehärtet wurden. Das Bild zeigt, daß an der Meßstelle M1 die Einhärtetiefe beim Versuch 1 größer ist (Kurve 1) als beim Versuch 2 (Kurve 2).The different carburizing effects of the method according to the invention and the conventional one becomes clear when one looks at the hardness curve of double spur gears (material 16 MCr5) which were case hardened in experiment 1 according to the method according to the invention or in experiment 2 according to the conventional method. The picture shows that the hardness depth at test point M1 is greater in test 1 (curve 1) than in test 2 (curve 2).

Die unterschiedliche Aufkohluqgswirkung der beiden Verfahren wird noch deutlicher, wenn man den Härteverlauf an der geometrisch ungünstigen Meßstelle M2 mißt. Der Härteverlauf an der Meßstelle M2 an einem Stirnrad aus Versuch 1 entspricht der Kurve 2, beim Versuch 2 wurde dagegen an der Meßstelle M2 keine Aufhärtung über 416 HV erreicht.The different carburizing effect of the two methods becomes even clearer if one measures the hardness curve at the geometrically unfavorable measuring point M2. The course of hardness at measuring point M2 on a spur gear from test 1 corresponds to curve 2; in test 2, however, no hardening above 416 HV was achieved at measuring point M2.

Zusammenfassend läßt sich feststellen, daß mit dem erfindungsgemäßen Verfahren nicht nur eine schnellere, sondern auch eine verbesserte Aufkohlung - insbesondere an geometrisch ungünstigen Stellen - erzielt wird.In summary, it can be stated that the method according to the invention not only achieves a faster carburization but also an improved carburization - in particular at geometrically unfavorable points.

Claims (5)

1. A method of case-hardening metallic workpieces, in which the latter are subjected to the act 3n of a carbon-containing gas atmosphere at high temperatures in a furnace, in which gas atmosphere pressure fluctuations are produced, characterised in that the gas atmosphere is formed from at least two components and the pressure fluctuations are produced by the pulsating charging into the furnace of at least two components having different amplitudes and frequencies of pressure fluctuations for the individual gas components.
2. A method as claimed in Claim 1, characterised in that the periodic duration of the pressure fluctuations is short in comparison with the duration of the heat treatment.
3. A method as claimed in one of Claims 1 or 2, characterised in that the gas mixture is formed from an inert carrier gas, a carbon-containing and nitrogen-containing gas, and a gas which contains oxygen, and the pressure fluctuations are produced by the pulsating addition of two gas components to the third gas component, or by mixing all gas components in a pulsating manner, as the case may be.
4. A method as claimed in one of Claims 1 to 3, characterised in that the carbon-containing gas is a hydrocarbon having at least two carbon atoms.
5. A method as claimed in one of Claims 1 to 4, characterised in that the frequency of the pressure fluctuations is adjusted in dependence upon the content of methane and/or hydrogen and/or soot in the furnace atmosphere.
EP81108035A 1980-10-08 1981-10-07 Method of case-hardening metallic pieces Expired EP0049531B1 (en)

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DE3038082 1980-10-08
DE19803038082 DE3038082A1 (en) 1980-10-08 1980-10-08 METHOD FOR USEFUL METAL WORKPIECES

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EP0049531B1 true EP0049531B1 (en) 1985-06-05

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FR835931A (en) * 1938-03-30 1939-01-05 Process for the gas carburizing of steel parts
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DE2851982A1 (en) * 1978-12-01 1980-06-12 Degussa Control of gas carburising at low pressures - involves pumping gas out of vacuum furnace and replacing it after it has decomposed by specific amt.

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AU542462B2 (en) 1985-02-21
NO813284L (en) 1982-04-13
ES505892A0 (en) 1982-09-01
DK433081A (en) 1982-04-09
DE3170867D1 (en) 1985-07-11
AU6915581A (en) 1982-04-22
ZA812499B (en) 1982-04-28
ATA539780A (en) 1982-04-15
ES8206641A1 (en) 1982-09-01
BR8102151A (en) 1982-08-17
EP0049531A1 (en) 1982-04-14
DE3038082A1 (en) 1982-05-06

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