EP0080124A2 - Process for case hardening metallic articles - Google Patents
Process for case hardening metallic articles Download PDFInfo
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- EP0080124A2 EP0080124A2 EP82110429A EP82110429A EP0080124A2 EP 0080124 A2 EP0080124 A2 EP 0080124A2 EP 82110429 A EP82110429 A EP 82110429A EP 82110429 A EP82110429 A EP 82110429A EP 0080124 A2 EP0080124 A2 EP 0080124A2
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- EP
- European Patent Office
- Prior art keywords
- carbon
- containing gas
- addition
- workpieces
- duration
- Prior art date
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- 238000000034 method Methods 0.000 title claims abstract description 39
- 230000008569 process Effects 0.000 title claims description 12
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 230000009471 action Effects 0.000 claims abstract description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 54
- 229910052799 carbon Inorganic materials 0.000 claims description 54
- 239000007789 gas Substances 0.000 claims description 45
- ATUOYWHBWRKTHZ-UHFFFAOYSA-N Propane Chemical compound CCC ATUOYWHBWRKTHZ-UHFFFAOYSA-N 0.000 claims description 34
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 30
- 239000001294 propane Substances 0.000 claims description 17
- 229910052757 nitrogen Inorganic materials 0.000 claims description 15
- 238000005255 carburizing Methods 0.000 claims description 7
- 239000011261 inert gas Substances 0.000 claims description 2
- 229930195733 hydrocarbon Natural products 0.000 description 9
- 239000004215 Carbon black (E152) Substances 0.000 description 7
- 150000002430 hydrocarbons Chemical class 0.000 description 7
- 239000004071 soot Substances 0.000 description 7
- 238000009792 diffusion process Methods 0.000 description 5
- 150000001247 metal acetylides Chemical class 0.000 description 5
- 238000000137 annealing Methods 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 3
- 238000005256 carbonitriding Methods 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000004992 fission Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000000819 phase cycle Methods 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
Images
Classifications
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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
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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
Definitions
- the invention relates to a method for case hardening metallic workpieces, wherein the workpieces are exposed to the action of a carbon-containing gas mixture, to which one or more carbon-containing gas components are added in a pulsating manner during their action on the workpieces.
- Pulsating addition of the carbon-containing gas component achieves a large carbon potential gradient in a method of the type mentioned above.
- Pulsating addition of a carbon-containing gas component means adding it to the gas mixture during numerous cycles consisting of two different phases. In the first phase of a cycle, the carbon-containing gas is added to the gas mixture in a pulsed manner and the carbon potential of the gas atmosphere is raised to a certain level. In the second phase, the supply of carbon-containing gas is interrupted, i.e. no carbon-containing gas is supplied to the gas mixture. This reduces the carbon potential of the gas atmosphere.
- the invention is therefore based on the object of specifying a method of the type mentioned at the outset with which workpieces can be carburized or carbonitrided uniformly, carbides formed being largely removed.
- This object is achieved in that the addition of the carbon-containing gas component (s) is interrupted after several cycles each consisting of a phase of the pulse-like addition of carbon-containing gas and a subsequent phase without the addition of carbon-containing gas and only after the end of one compared to Duration of a cycle long pause is resumed.
- the carburizing or carbonitriding process is no longer divided into two-phase cycles. Rather, the case hardening method according to the invention is composed of several intervals, each consisting of several cycles followed by a pause. As in the known method, cycle is to be understood as the brief addition of a hydrocarbon to the gas mixture with subsequent interruption of the hydrocarbon supply.
- the carbon concentration in the edge area of the workpieces drops in every interval. At the beginning of the next interval, therefore, is the gradient of the Koh and the carbon transfer in the workpiece is very high.
- the amount of carbon-containing gas supplied in a cycle or the number of cycles is selected such that the supply of the carbon-containing gas is cut off as soon as carbon saturation is reached in the edge layer of the workpieces.
- the total carburizing time is made up of the periods in which carbon is introduced into the workpiece and the periods in which the carbon diffuses in the workpiece. According to the invention, the duration of the carbon introduction is considerably shorter than that of the diffusion.
- the process according to the invention causes the very stable carbides to dissolve during an interval, so that an excellent, surface oxidation-free surface quality of the workpieces is achieved. Because of this feature, the proposed method can also be used in push-through furnaces.
- the amount of nitrogen supplied per unit of time is increased for the duration of the pulsating addition of the carbon-containing gas component (s).
- the furnace in which the workpieces are treated is constantly gassed with nitrogen to ensure an inert basic gas atmosphere in the furnace chamber.
- the amount of nitrogen is increased for the duration of the pulsating hydrocarbon addition in order not to let the concentration of the hydrocarbon radicals become too high. Otherwise they would react with each other and form soot and would no longer contribute to carburization.
- the pause lasts by a factor of 10 to 100 times longer than the previous cycles.
- carbide compounds are still largely eliminated, but the duration of the case hardening process is minimal.
- a particularly simple regulation is possible in the method according to the invention if, according to an advantageous variant, the duration of the cycles is kept constant during case hardening.
- the carbon-containing gas is consequently pulsed into the furnace chamber at constant time intervals.
- the gas atmosphere is formed exclusively from an inert gas, in particular nitrogen, and a carbon-containing gas, in particular propane.
- An annealing furnace 1 is connected via a line 2 to a soot sensor 3 and a control unit 4.
- the gas components nitrogen and a hydrocarbon in the exemplary embodiment propane, are now introduced into the annealing furnace 1.
- Supply lines 5 (nitrogen) and 6 (propane) are used for this.
- Valves 7, 8, 9, 10 and 11 control the addition of nitrogen and propane from the suitable tanks in which these components are stored in liquid form. Nitrogen and propane are mixed before entering the annealing furnace 1 and passed into the furnace via a line 12.
- valve 9 in a line 13 is open, while valves 7 and 10 are closed. At this point, the furnace atmosphere consists essentially of nitrogen.
- the carburizing or carbonitriding process begins as soon as a suitable temperature of approx. 800 to 1000 ° C has been reached in the furnace.
- solenoid valve 10 is opened according to the invention.
- Valve 10 is opened and closed by control unit 4 at constant time intervals.
- a certain amount of nitrogen is always passed into the furnace per unit time during case hardening.
- the amount of nitrogen supplied is increased in order not to make the concentration of the hydrocarbon radicals too great. Otherwise the radicals would react with one another and form soot.
- solenoid valve 7 is in a bypass Line 14 opened by the control unit 4.
- the propane is unstable at the high temperatures prevailing in the interior of the annealing furnace and disintegrates spontaneously.
- the fission products are very reactive and enable the workpiece surface layer to be saturated quickly with carbon. Because of the resulting significant carbon potential difference between the workpiece surface and the core, the carbon quickly diffuses into the edge layer of the workpieces.
- Soot can now be formed in the gas mixture.
- the amount of propane is reduced before a minimum soot value is reached.
- the value determined by the sensor 3 is sent to the control unit 4, in which the measured value is compared with a predetermined setpoint signal. A difference between the measured value signal and the desired value signal is converted into a signal by which a control valve 11 in the supply line 6 for propane is controlled.
- valve 10 - triggered by control unit 4 - is closed for a pause which lasts longer than the previous cycles and only nitrogen is fed into the furnace via line 13 with valve 9.
- the carbon concentration in the edge region of the workpiece drops again, so that at the beginning of the interval consisting of several cycles with a subsequent pause, the gradient and thus the carbon transition into the workpiece is high.
- the carbon not only diffuses into the workpiece, but also the unwanted carbides on the workpiece surface are redissolved and removed.
- valves 7 and 10 are closed and the workpieces are lowered to the hardening temperature.
- the carbon content in the gas mixture (e.g. in% by volume) is shown schematically against time (in seconds).
- an interval of the method according to the invention is shown which lasts from the time zero to the time T '.
- the carbon content of the gas mixture is briefly increased in several cycles, each of which takes time t.
- a cycle consists of phase I (duration t 1 ) and phase II (duration t 2 ).
- phase I propane is added to the gas mixture in pulses, while in phase II no propane is added to the gas mixture.
- phase II the carbon content therefore decreases.
- the carbon content does not drop to 0. It is only in the pause (duration T) that follows after several cycles (only the first four cycles in the first interval are shown in the sketch), in which no propane is fed into the furnace the carbon content to 0.
- a typical interval contains up to 15 cycles.
- the addition periods depend on the furnace volume and the tightness of the furnace.
- phase I lasts 5 to 15 seconds
- phase II on the other hand, 15 to 60 seconds.
- T 30 minutes
- the method according to the invention enables rapid case hardening of workpieces with low consumption of carbon carriers. Since carbides formed are redissolved by the procedure according to the invention, piercing furnaces can also be used. be used in this process.
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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)
- Contacts (AREA)
- Regulation And Control Of Combustion (AREA)
- Arc Welding Control (AREA)
Abstract
Description
Die Erfindung betrifft ein Verfahren zum Einsatzhärten metallischer Werkstücke, wobei die Werkstücke der Einwirkung eines kohlenstoffhaltigen Gasgemisches ausgesetzt werden, dem eine oder mehrere kohlenstoffhaltige Gaskompo- nente(n) während dessen Einwirkung auf die Werkstücke pulsierend zugegeben wird (werden).The invention relates to a method for case hardening metallic workpieces, wherein the workpieces are exposed to the action of a carbon-containing gas mixture, to which one or more carbon-containing gas components are added in a pulsating manner during their action on the workpieces.
Durch das pulsierende Zugeben der kohlenstoffhaltigen Gaskomponente wird bei einem Verfahren der vorstehend genannten Art ein großes Kohlenstoffpotentialgefälle erreicht. Pulsierendes Zugeben einer kohlenstoffhaltigen Gaskomponente bedeutet, diese während zahlreicher, sich aus zwei verschiedenen Phasen zusammensetzenden Zyklen dem Gasgemisch zuzugeben. In der ersten Phase eines Zyklus wird das kohlenstoffhaltige Gas pulsartig dem Gasgemisch zugemischt und das Kohlenstoffpotential der Gasatmosphäre auf ein bestimmtes Niveau gehoben. In der zweiten Phase wird die Zufuhr von kohlenstoffhaltigem Gas unterbrochen, d.h. dem Gasgemisch wird kein kohlenstoffhaltiges Gas zugeführt. Dadurch sinkt das Kohlenstoffpotential der Gasatmosphäre.The pulsating addition of the carbon-containing gas component achieves a large carbon potential gradient in a method of the type mentioned above. Pulsating addition of a carbon-containing gas component means adding it to the gas mixture during numerous cycles consisting of two different phases. In the first phase of a cycle, the carbon-containing gas is added to the gas mixture in a pulsed manner and the carbon potential of the gas atmosphere is raised to a certain level. In the second phase, the supply of carbon-containing gas is interrupted, i.e. no carbon-containing gas is supplied to the gas mixture. This reduces the carbon potential of the gas atmosphere.
Bei dieser Verfahrensweise wird das Werkstück in einer 'sehr dünnen Schicht stark überkohlt. Die in der zweiten Phase sich anschließende Diffusion verläuft nun sehr rasch und schafft in der Randschicht des Werkstückes neue Aufnahmekapazität für Kohlenstoff.With this procedure, the workpiece is heavily carburized in a 'very thin layer. The diffusion that follows in the second phase now runs very quickly and creates new absorption capacity for carbon in the edge layer of the workpiece.
Durch pulsierende Zugabe von kohlenstoffhaltigen Gaskomponenten wird ein hoher, gleichmäßiger Kohlenstoffeintrag bis über die Sättigung hinaus möglich. Bei dieser Art des Einsatzhärtens bilden sich Karbide, die sich zu einem gewissen Teil während der zweiten Phase eines Zyklus auflösen. Eine vollständige Auflösung der sehr stabilen Karbidverbindungen war bisher innerhalb eines Zyklus jedoch nicht möglich.The pulsating addition of carbon-containing gas components enables a high, even carbon input up to and beyond saturation. This type of case hardening forms carbides, which dissolve to a certain extent during the second phase of a cycle. However, a complete dissolution of the very stable carbide compounds was not possible within one cycle.
Insbesondere diese Tatsache verhinderte die Anwendung des bekannten Verfahrens in einem Durchstoßofen, den die Werkstücke (Chargen) in mehreren, zeitlich konstanten Takten durchlaufen.This fact in particular prevented the use of the known method in a push-through furnace through which the workpieces (batches) pass in several, time-constant cycles.
Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren der eingangs erwähnten Art anzugeben, mit dem Werkstücke gleichmäßig aufgekohlt bzw. karbonitriert werden können, wobei gebildete Karbide weitgehend entfernt werden.The invention is therefore based on the object of specifying a method of the type mentioned at the outset with which workpieces can be carburized or carbonitrided uniformly, carbides formed being largely removed.
Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß die Zugabe der kohlenstoffhaltigen Gaskomponente(n) nach mehreren der sich jeweils aus einer Phase der pulsartigen Zugabe von kohlenstoffhaltigem Gas und einer darauffolgenden Phase ohne Zugabe von kohlenstoffhaltigem Gas zusammensetzenden Zyklen unterbrochen und erst nach Ablauf einer im Vergleich zur Dauer eines Zyklus langen Pause wieder aufgenommen wird.This object is achieved in that the addition of the carbon-containing gas component (s) is interrupted after several cycles each consisting of a phase of the pulse-like addition of carbon-containing gas and a subsequent phase without the addition of carbon-containing gas and only after the end of one compared to Duration of a cycle long pause is resumed.
Erfindungsgemäß wird der Aufkohlungs- bzw. Karbonitrierungsprozeß nicht mehr ausschließlich in aus zwei Phasen bestehenden Zyklen unterteilt. Vielmehr setzt sich das erfindungsgemäße Verfahren zum Einsatzhärten aus mehreren Intervallen zusammen, die jeweils aus mehreren Zyklen mit anschließender Pause bestehen. Unter Zyklus ist - wie beim bekannten Verfahren - die kurzzeitige Zugabe eines Kohlenwasserstoffs zum Gasgemisch mit anschließender Unterbrechung der Kohlenwasserstoffzufuhr zu verstehen.According to the carburizing or carbonitriding process is no longer divided into two-phase cycles. Rather, the case hardening method according to the invention is composed of several intervals, each consisting of several cycles followed by a pause. As in the known method, cycle is to be understood as the brief addition of a hydrocarbon to the gas mixture with subsequent interruption of the hydrocarbon supply.
Beim herkömmlichen Verfahren sinkt das Kohlenstoffpotential während des Einsatzhärte-Prozesses nie auf Null ab. Dabei wird durch die pulsierende Zugabe der Kohlenwasserstoffe ein überschreiten der Rußgrenze vermieden. Dem erfindungsgemäßen Verfahren liegt nun die Erkenntnis zugrunde, daß die Dauer der Phase, in der während eines Zyklus kein Kohlenwasserstoff dem Gasgemisch zugegeben wird, für eine optimale Diffusion und eine Auflösung der sehr stabilen Karbidverbindungen nicht ausreicht.In the conventional process, the carbon potential never drops to zero during the case hardening process. The pulsating addition of hydrocarbons prevents the soot limit from being exceeded. The method according to the invention is now based on the knowledge that the duration of the phase in which no hydrocarbon is added to the gas mixture during a cycle is not sufficient for optimal diffusion and dissolution of the very stable carbide compounds.
Durch die sehr große Reaktivität der aufgespaltenen Kohlenwasserstoffe ist der eigentliche Aufkohlungsprozeß äußerst kurz gegenüber den Diffusionsphasen. Ihre Länge hängt ab von der aktuellen Aufkohlungstiefe. Je größer diese wird, desto langsamer diffundiert der neueingebrachte Kohlenstoff nach innen.Due to the very high reactivity of the split hydrocarbons, the actual carburization process is extremely short compared to the diffusion phases. Its length depends on the current carburization depth. The larger this becomes, the more slowly the newly introduced carbon diffuses inwards.
Erfindungsgemäß wird nun - wie beim bekannten Verfahren - zu Beginn eines Intervalls ein sehr hohes Kohlenstoffpotential erreicht. Nach mehreren Zyklen wird jedoch eine Pause eingelegt, die im Vergleich zur Dauer eines Zyklus lang ist.According to the invention, a very high carbon potential is now reached at the beginning of an interval, as in the known method. After several cycles, however, there is a pause that is long compared to the duration of a cycle.
Während dieser Pause sinkt die Kohlenstoffkonzentration im Randbereich der Werkstücke in jedem Intervall ab. Zu Beginn des nächsten Intervalls ist daher der Gradient des Kohlenstoffgehaltes und damit der Kohlenstoffübergang im Werkstück sehr hoch. Die in einem Zyklus zugeführte Menge kohlenstoffhaltigen Gases bzw. die Zahl der Zyklen wird so gewählt, daß die Zufuhr des kohlenstoffhaltigen Gases abgestellt wird, sobald in der Randschicht der Werkstücke eine Sättigung mit Kohlenstoff erreicht ist. Die gesamte Aufkohlungszeit setzt sich zusammen aus den Zeitabschnitten, in denen Kohlenstoff in das Werkstück eingetragen wird und den Zeitabschnitten, in denen der Kohlenstoff im Werkstück diffundiert. Erfindungsgemäß ist die Dauer des Kohlenstoffeintrags wesentlich geringer als die der Diffusion.During this pause, the carbon concentration in the edge area of the workpieces drops in every interval. At the beginning of the next interval, therefore, is the gradient of the Koh and the carbon transfer in the workpiece is very high. The amount of carbon-containing gas supplied in a cycle or the number of cycles is selected such that the supply of the carbon-containing gas is cut off as soon as carbon saturation is reached in the edge layer of the workpieces. The total carburizing time is made up of the periods in which carbon is introduced into the workpiece and the periods in which the carbon diffuses in the workpiece. According to the invention, the duration of the carbon introduction is considerably shorter than that of the diffusion.
Es wurde festgestellt, daß das erfindungsgemäße Verfahren während eines Intervalls eine Auflösung der sehr stabilen Karbide bewirkt, so daß eine hervorragende, randoxidationsfreie Oberflächenqualität der Werkstücke erzielt wird. Aufgrund dieses Merkmals kann das vorgeschlagene Verfahren auch bei Durchstoßöfen Anwendung finden.It was found that the process according to the invention causes the very stable carbides to dissolve during an interval, so that an excellent, surface oxidation-free surface quality of the workpieces is achieved. Because of this feature, the proposed method can also be used in push-through furnaces.
Weiterhin wurde gefunden, daß im Vergleich zum bekannten Verfahren eine wesentlich geringere Zahl an Zyklen ausreicht, um die gleiche Einhärtetiefe zu erzielen. Außerdem liegt der durchschnittliche Verbrauch an kohlenstoffhaltigem Gas, beispielsweise Propan, niedriger als beim bekannten Verfahren.Furthermore, it was found that, compared to the known method, a significantly smaller number of cycles is sufficient to achieve the same hardening depth. In addition, the average consumption of carbon-containing gas, for example propane, is lower than in the known method.
In einer vorteilhaften Ausgestaltung des Erfindungsgedankens, bei dem dem Gasgemisch Stickstoff zugeführt wird, wird die pro Zeiteinheit zugeführte Stickstoffmenge für die Dauer der pulsierenden Zugabe der kohlenstoffhaltigen Gaskomponente(n) erhöht.In an advantageous embodiment of the inventive concept, in which nitrogen is added to the gas mixture, the amount of nitrogen supplied per unit of time is increased for the duration of the pulsating addition of the carbon-containing gas component (s).
In dieser Variante wird der Ofen, in dem die Werkstücke behandelt werden, ständig mit Stickstoff begast, um im Ofenraum eine inerte Grundgasatmosphäre zu gewährleisten.In this variant, the furnace in which the workpieces are treated is constantly gassed with nitrogen to ensure an inert basic gas atmosphere in the furnace chamber.
Bei Erreichen der gewählten Aufkohlungstemperatur wird für die Dauer der pulsierenden Kohlenwasserstoffzugabe die Stickstoffmenge erhöht, um die Konzentration der Kohlenwasserstoffradikale nicht zu groß werden zu lassen. Andernfalls würden sie untereinander reagieren und Ruß bilden und nicht mehr zur Aufkohlung beitragen.When the selected carburizing temperature is reached, the amount of nitrogen is increased for the duration of the pulsating hydrocarbon addition in order not to let the concentration of the hydrocarbon radicals become too high. Otherwise they would react with each other and form soot and would no longer contribute to carburization.
Nach einem Merkmal des erfindungsgemäßen Verfahrens ist es besonders wirtschaftlich, wenn die Pause um einen Faktor 10 bis 100 länger als die vorangegangenen Zyklen dauert. In dieser Variante werden Karbidverbindungen nach wie vor weitgehend beseitigt, die Dauer des Einsatzhärte-Prozesses ist jedoch minimal.According to one feature of the method according to the invention, it is particularly economical if the pause lasts by a factor of 10 to 100 times longer than the previous cycles. In this variant, carbide compounds are still largely eliminated, but the duration of the case hardening process is minimal.
Der Diffusionsvorgang erfolgt wegen des geringer werdenden Kohlenstoffpotentialgefälles mit zunehmender Aufkohlungstiefe langsamer. Mit Vorteil werden daher die Pausen mit zunehmender Dauer des Aufkohlungsvorganges verlängert.Due to the decreasing carbon potential gradient, the diffusion process takes place more slowly with increasing depth of carburization. The breaks are therefore advantageously extended with increasing duration of the carburizing process.
Eine besonders einfache Regelung ist beim erfindungsgemäßen Verfahren möglich, wenn nach einer vorteilhaften Variante die Dauer der Zyklen während des Einsatzhärtens konstant gehalten wird. Das kohlenstoffhaltige Gas wird folglich in konstanten Zeitabständen pulsartig in den Ofenraum gegeben.A particularly simple regulation is possible in the method according to the invention if, according to an advantageous variant, the duration of the cycles is kept constant during case hardening. The carbon-containing gas is consequently pulsed into the furnace chamber at constant time intervals.
In einer weiteren Ausgestaltung der Erfindung wird die Gasatmosphäre ausschließlich aus einem inerten Gas, insbesondere Stickstoff, und einem kohlenstoffhaltigen Gas, insbesondere Propan, gebildet.In a further embodiment of the invention, the gas atmosphere is formed exclusively from an inert gas, in particular nitrogen, and a carbon-containing gas, in particular propane.
Im folgenden soll anhand schematischer Skizzen ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens erläutert werden.An exemplary embodiment of the method according to the invention is to be explained below with the aid of schematic sketches.
Es zeigen:
- Figur 1 eine schematische Darstellung einer Anlage, in der das erfindungsgemäße Verfahren durchgeführt werden kann,
Figur 2 den zeitlichen Verlauf des Kohlenstoffgehaltes im Aufkohlungsgas.
- FIG. 1 shows a schematic representation of a plant in which the method according to the invention can be carried out,
- Figure 2 shows the time course of the carbon content in the carburizing gas.
Ein Glühofen 1 ist über eine Leitung 2 mit einem Rußsensor 3 und einer Regeleinheit 4 verbunden. Erfindungsgemäß werden nun die Gaskomponenten Stickstoff und ein Kohlenwasserstoff, im Ausführungsbeispiel Propan, in den Glühofen 1 eingeleitet. Hierzu dienen Zuführleitungen 5 (Stickstoff) und 6 (Propan). Durch Ventile 7, 8, 9, 10 und 11 wird die Zugabe von Stickstoff und Propan, die geeigneten Tanks, in denen diese Komponenten flüssig gespeichert werden, entnommen wurden, gesteuert. Stickstoff und Propan werden vor dem Eintritt in den Glühofen 1 vermischt und über eine Leitung 12 in den Ofen geleitet. Beim Einfahren der Charge in den Ofenraum ist Ventil 9 in einer Leitung 13 geöffnet, während Ventile 7 und 10 geschlossen sind. Die Ofenatmosphäre besteht zu diesem Zeitpunkt im wesentlichen aus Stickstoff. Der Aufkohlungs- bzw. Karbonitrierungsvorgang beginnt, sobald eine geeignete Temperatur von ca. 800 bis 1000°C im Ofen erreicht worden ist. Um die Werkstücke im Ofenraum einem Gasgemisch mit einem hohen Kohlenstoffpotential auszusetzen, wird erfindungsgemäß Magnetventil 10 geöffnet. Ventil 10 wird von der Regeleinheit 4 in zeitlich konstanten Abständen geöffnet und geschlossen. Erfindungsgemäß wird während des Einsatzhärtens stets eine bestimmte Menge Stickstoff pro Zeiteinheit in den Ofen geleitet. Während der Phasen, in denen Propan kurzzeitig in den Ofen eingespeist wird, wird die zugeführte Stickstoffmenge erhöht um die Konzentration der Kohlenwasserstoffradikale nicht zu groß werden zu lassen. Andernfalls würden die Radikale untereinander reagieren und Ruß bilden. Zu diesem Zweck wird Magnetventil 7 in einer Bypaßleitung 14 von der Regeleinheit 4 geöffnet.An annealing furnace 1 is connected via a
Das Propan ist bei den hohen im Glühofeninnenraum herrschenden Temperaturen instabil und zerfällt spontan. Die Spaltprodukte sind sehr reaktionsfreudig und ermgölichen eine rasch ablaufende Sättigung der Werkstückrandschicht mit Kohlenstoff. Wegen des daraus resultierenden erheblichen Kohlenstoffpotentialgefälles zwischen Werkstückoberfläche und Kern diffundiert der Kohlenstoff rasch in die Randschicht der Werkstücke.The propane is unstable at the high temperatures prevailing in the interior of the annealing furnace and disintegrates spontaneously. The fission products are very reactive and enable the workpiece surface layer to be saturated quickly with carbon. Because of the resulting significant carbon potential difference between the workpiece surface and the core, the carbon quickly diffuses into the edge layer of the workpieces.
Im Gasgemisch kann nun Ruß gebildet werden. Vor Erreichen eines minimalen Rußwertes wird die Propanmenge reduziert. Der vom Sensor 3 ermittelte Werte wird an die Regeleinheit 4 geleitet, in der der Meßwert mit einem vorgegebenen Sollwertsignal verglichen wird. Eine Differenz zwischen Meßwert-und Sollwertsignal wird in ein Signal umgesetzt, durch das ein Regelventil 11 in der Zufuhrleitung 6 für Propan gesteuert wird.Soot can now be formed in the gas mixture. The amount of propane is reduced before a minimum soot value is reached. The value determined by the
Beim überschreiten des dem Sollwert entsprechenden Rußwertes wird die Propanmenge durch Regelventil 11 soweit vermindert, bis Ist- und Sollwert wieder übereinstimmen.When the soot value corresponding to the target value is exceeded, the amount of propane is reduced by
Nach mehreren Zyklen, in denen in einer ersten Phase kurzzeitig Propan in den Ofen geleitet bzw. in einer zweiten Phase die Propanzufuhr unterbrochen worden ist, wird Ventil 10 - ausgelöst durch Regeleinheit 4 - für eine Pause, die länger dauert als die vorangegangenen Zyklen, geschlossen und nur Stickstoff über Leitung 13mit Ventil 9 in den Ofen geleitet. In dieser Pause sinkt die Kohlenstoffkonzentration im Randbereich des Werkstückes wieder ab, so daß bei Beginn des sich aus mehreren Zyklen mit anschließender Pause zusammensetzenden Intervalls der Gradient und damit der Kohlenstoffübergang ins Werkstück hoch ist. In den Pausen diffundiert der Kohlenstoff nicht nur in das Werkstück, sondern es werden auch die unerwünschten Karbide auf der Werkstückoberfläche rückgelöst und entfernt.After several cycles in which propane was briefly fed into the furnace in a first phase or the propane supply was interrupted in a second phase, valve 10 - triggered by control unit 4 - is closed for a pause which lasts longer than the previous cycles and only nitrogen is fed into the furnace via
Nach mehreren Intervallen werden die Ventile 7 und 10 geschlossen und die Werkstücke auf Härtetemperatur abgesenkt.After several intervals, valves 7 and 10 are closed and the workpieces are lowered to the hardening temperature.
In Figur 2 ist nun der Kohlenstoffgehalt im Gasgemisch (z.B. in Vol.%) gegen die Zeit (in Sekunden) schematisch dargestellt.In Figure 2, the carbon content in the gas mixture (e.g. in% by volume) is shown schematically against time (in seconds).
Im wesentlichen ist ein Intervall des erfindungsgemäßen Verfahrens dargestellt, das vom Zeitnullpunkt bis zum Zeitpunkt T' dauert. Zu Beginn des Intervalls wird der Kohlenstoffgehalt des Gasgemisches in mehreren Zyklen, die jeweils die Zeitspanne t dauern, kurzzeitig angehoben. Ein Zyklus setzt sich aus der Phase I (Dauer t1) und der Phase II (Dauer t2) zusammen. Wie bereits geschildert, wird in Phase I Propan impulsartig dem Gasgemisch zugegeben, während in Phase II kein Propan dem Gasgemisch zugegeben wird. In Phase I steigt, in Phase II sinkt daher der Kohlenstoffgehalt. Während der Zyklen sinkt der Kohlenstoffgehalt jedoch nicht auf 0. Erst in der sich an mehrere Zyklen (in der Skizze sind lediglich die ersten vier Zyklen im ersten Intervall dargestellt) anschließenden Pause (Dauer T), in der kein Propan dem Ofen zugeleitet wird, sinkt der Kohlenstoffgehalt auf 0.Essentially, an interval of the method according to the invention is shown which lasts from the time zero to the time T '. At the beginning of the interval, the carbon content of the gas mixture is briefly increased in several cycles, each of which takes time t. A cycle consists of phase I (duration t 1 ) and phase II (duration t 2 ). As already described, in phase I propane is added to the gas mixture in pulses, while in phase II no propane is added to the gas mixture. In phase I increases, in phase II the carbon content therefore decreases. During the cycles, however, the carbon content does not drop to 0. It is only in the pause (duration T) that follows after several cycles (only the first four cycles in the first interval are shown in the sketch), in which no propane is fed into the furnace the carbon content to 0.
Ein typisches Intervall enthält beispielsweise bis zu 15 Zyklen. Die Zugabeperioden hängen vom Ofenvolumen und der Ofendichtigkeit ab. Phase I dauert beispielsweise 5 bis 15 sec., Phase II dagegen 15 bis 60 sec. An mehrere Zyklen (beispielsweise 10 mit Gesamtdauer 5 Minuten) schließt sich eine Pause von z.B. T = 30 Minuten an, so daß ein Intervall etwa 35 Minuten dauert. Bei gleicher Einhärtetiefe reduziert sich die Zahl der Zyklen des erfindungsgemäßen Verfahrens im Vergleich zum bekannten Verfahren ca. um einen Faktor 3.For example, a typical interval contains up to 15 cycles. The addition periods depend on the furnace volume and the tightness of the furnace. For example, phase I lasts 5 to 15 seconds, phase II, on the other hand, 15 to 60 seconds. Several cycles (for example 10 with a total duration of 5 minutes) are followed by a pause of, for example, T = 30 minutes, so that an interval lasts about 35 minutes. Reduced with the same hardening depth the number of cycles of the method according to the invention is approximately a factor of 3 compared to the known method.
Zusammenfassend ist festzustellen, daß das erfindungsgemäße Verfahren ein rasches Einsatzhärten von Werkstücken bei geringem Verbrauch an Kohlenstoffträger ermöglicht. Da gebildete Karbide durch die erfindungsgemäße Verfahrensweise rückgelöst werden, können auch Durchstoßöfen. bei diesem Verfahren eingesetzt werden.In summary, it can be stated that the method according to the invention enables rapid case hardening of workpieces with low consumption of carbon carriers. Since carbides formed are redissolved by the procedure according to the invention, piercing furnaces can also be used. be used in this process.
Claims (6)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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DE3146042 | 1981-11-20 | ||
DE19813146042 DE3146042A1 (en) | 1981-11-20 | 1981-11-20 | METHOD FOR USEFUL METAL WORKPIECES |
Publications (3)
Publication Number | Publication Date |
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EP0080124A2 true EP0080124A2 (en) | 1983-06-01 |
EP0080124A3 EP0080124A3 (en) | 1984-08-22 |
EP0080124B1 EP0080124B1 (en) | 1986-09-24 |
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Application Number | Title | Priority Date | Filing Date |
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EP82110429A Expired EP0080124B1 (en) | 1981-11-20 | 1982-11-11 | Process for case hardening metallic articles |
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EP (1) | EP0080124B1 (en) |
AT (1) | AT373294B (en) |
AU (1) | AU548340B2 (en) |
BR (1) | BR8206714A (en) |
DE (2) | DE3146042A1 (en) |
ES (1) | ES8307921A1 (en) |
GR (1) | GR77758B (en) |
NO (1) | NO823887L (en) |
ZA (1) | ZA828553B (en) |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0408511A1 (en) * | 1989-07-13 | 1991-01-16 | Solo Fours Industriels Sa | Process and apparatus for thermal or thermochemical treatment of steel |
FR2656003A1 (en) * | 1989-12-14 | 1991-06-21 | Gantois Michel | Process and plant for the heat- or thermochemical treatment of a steel making it possible to control the carbon enrichment of the surface region |
FR2681332A1 (en) * | 1991-09-13 | 1993-03-19 | Innovatique Sa | METHOD AND DEVICE FOR CUTTING STEEL IN A LOW PRESSURE ATMOSPHERE. |
WO2001055470A2 (en) * | 2000-01-28 | 2001-08-02 | Swagelok Company | Modified low temperature case hardening processes |
EP1160349A1 (en) * | 2000-05-24 | 2001-12-05 | Ipsen International GmbH | Process and apparatus for heat treating of metallic workpieces |
FR2821362A1 (en) * | 2001-02-23 | 2002-08-30 | Etudes Const Mecaniques | LOW PRESSURE CEMENTING PROCESS |
WO2003097893A1 (en) * | 2002-05-15 | 2003-11-27 | Linde Aktiengesellschaft | Method and device for heat treatment of metallic work pieces |
EP2034038A3 (en) * | 2007-08-17 | 2009-09-02 | Robert Bosch GmbH | Method for producing an anti-wear layer on a magnetic component |
WO2012048669A1 (en) | 2010-10-11 | 2012-04-19 | Ipsen International Gmbh | Method and arrangement for carburizing and carbonitriding metallic materials |
US8828150B2 (en) | 2007-10-01 | 2014-09-09 | Robert Bosch Gmbh | Method for carburizing workpieces and its application |
EP2541176A3 (en) * | 2005-11-23 | 2014-09-24 | Surface Combustion, Inc. | Fluid delivery system for an atmospheric furnace used for treating one or more articles |
Families Citing this family (1)
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CN103556106B (en) * | 2013-10-30 | 2015-10-28 | 西安航空动力股份有限公司 | A kind of preparation method of 1Cr17Ni2 alloy material high-temperature vacuum cementation zone |
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EP0049530A1 (en) * | 1980-10-08 | 1982-04-14 | Linde Aktiengesellschaft | Method and device for carbonizing metallic pieces |
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- 1981-11-20 DE DE19813146042 patent/DE3146042A1/en not_active Withdrawn
-
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- 1982-03-04 AT AT0084282A patent/AT373294B/en not_active IP Right Cessation
- 1982-11-11 DE DE8282110429T patent/DE3273483D1/en not_active Expired
- 1982-11-11 AU AU90401/82A patent/AU548340B2/en not_active Ceased
- 1982-11-11 EP EP82110429A patent/EP0080124B1/en not_active Expired
- 1982-11-16 GR GR69832A patent/GR77758B/el unknown
- 1982-11-19 ES ES517532A patent/ES8307921A1/en not_active Expired
- 1982-11-19 NO NO823887A patent/NO823887L/en unknown
- 1982-11-19 BR BR8206714A patent/BR8206714A/en unknown
- 1982-11-19 ZA ZA828553A patent/ZA828553B/en unknown
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Cited By (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0408511A1 (en) * | 1989-07-13 | 1991-01-16 | Solo Fours Industriels Sa | Process and apparatus for thermal or thermochemical treatment of steel |
FR2656003A1 (en) * | 1989-12-14 | 1991-06-21 | Gantois Michel | Process and plant for the heat- or thermochemical treatment of a steel making it possible to control the carbon enrichment of the surface region |
FR2681332A1 (en) * | 1991-09-13 | 1993-03-19 | Innovatique Sa | METHOD AND DEVICE FOR CUTTING STEEL IN A LOW PRESSURE ATMOSPHERE. |
US6547888B1 (en) | 2000-01-28 | 2003-04-15 | Swagelok Company | Modified low temperature case hardening processes |
WO2001055470A2 (en) * | 2000-01-28 | 2001-08-02 | Swagelok Company | Modified low temperature case hardening processes |
WO2001055470A3 (en) * | 2000-01-28 | 2001-12-27 | Swagelok Co | Modified low temperature case hardening processes |
EP1160349A1 (en) * | 2000-05-24 | 2001-12-05 | Ipsen International GmbH | Process and apparatus for heat treating of metallic workpieces |
WO2002068707A1 (en) * | 2001-02-23 | 2002-09-06 | Etudes Et Constructions Mecaniques | Low-pressure carburising method |
FR2821362A1 (en) * | 2001-02-23 | 2002-08-30 | Etudes Const Mecaniques | LOW PRESSURE CEMENTING PROCESS |
US7118634B2 (en) | 2001-02-23 | 2006-10-10 | Bnp Parlbas | Low-pressure cementation method |
WO2003097893A1 (en) * | 2002-05-15 | 2003-11-27 | Linde Aktiengesellschaft | Method and device for heat treatment of metallic work pieces |
EP2541176A3 (en) * | 2005-11-23 | 2014-09-24 | Surface Combustion, Inc. | Fluid delivery system for an atmospheric furnace used for treating one or more articles |
EP2541177A3 (en) * | 2005-11-23 | 2014-09-24 | Surface Combustion, Inc. | Fluid delivery system for an atmospheric furnace used for treating one or more articles |
EP2034038A3 (en) * | 2007-08-17 | 2009-09-02 | Robert Bosch GmbH | Method for producing an anti-wear layer on a magnetic component |
US8828150B2 (en) | 2007-10-01 | 2014-09-09 | Robert Bosch Gmbh | Method for carburizing workpieces and its application |
WO2012048669A1 (en) | 2010-10-11 | 2012-04-19 | Ipsen International Gmbh | Method and arrangement for carburizing and carbonitriding metallic materials |
Also Published As
Publication number | Publication date |
---|---|
AT373294B (en) | 1984-01-10 |
BR8206714A (en) | 1983-10-04 |
GR77758B (en) | 1984-09-25 |
AU9040182A (en) | 1983-05-26 |
EP0080124B1 (en) | 1986-09-24 |
EP0080124A3 (en) | 1984-08-22 |
DE3146042A1 (en) | 1983-05-26 |
ATA84282A (en) | 1983-05-15 |
ES517532A0 (en) | 1983-08-01 |
ES8307921A1 (en) | 1983-08-01 |
NO823887L (en) | 1983-05-24 |
AU548340B2 (en) | 1985-12-05 |
ZA828553B (en) | 1983-09-28 |
DE3273483D1 (en) | 1986-10-30 |
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