EP0655512A1 - Method for producing unitary oxidic layers on metallic substrates and apparatus for carrying out the process - Google Patents
Method for producing unitary oxidic layers on metallic substrates and apparatus for carrying out the process Download PDFInfo
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- EP0655512A1 EP0655512A1 EP94116881A EP94116881A EP0655512A1 EP 0655512 A1 EP0655512 A1 EP 0655512A1 EP 94116881 A EP94116881 A EP 94116881A EP 94116881 A EP94116881 A EP 94116881A EP 0655512 A1 EP0655512 A1 EP 0655512A1
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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
- C21D1/06—Surface hardening
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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
- C23C8/34—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 more than one element being applied in more than one step
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- the invention relates to a process for producing uniform oxidation layers on metallic workpieces following a nitriding or nitrocarburizing process, the workpieces being exposed to an oxidizing atmosphere for a predetermined time after the nitriding or nitrocarburizing at a given temperature.
- the generic methods are used to improve the wear and corrosion resistance of the surfaces of components made of ferrous materials.
- the nitrocarburizing process is carried out as a special nitriding process at temperatures between 570 ° C and 700 ° C. This minimizes the delay.
- the workpieces are exposed to an oxidation atmosphere.
- the post-oxidation can significantly increase the wear resistance and in particular the corrosion resistance of the nitrocarburized surfaces.
- the workpieces are oxidized in an oxygen-containing atmosphere in an atmosphere-sphere furnace after the nitriding or nitrocarburizing.
- This post-oxidation normally takes place at temperatures between 500 ° C and 550 ° C, but is not limited to this range. Air, water vapor, CO2, laughing gas and mixtures of these gases with nitrogen or ammonia are primarily used for the oxidation.
- the aim of the post-oxidation is to convert the outer edge layer of the workpieces, which essentially consists of iron nitrides or carbonitrides, into a thin iron oxide layer. Ideally, an iron oxide layer of the form Fe3O4 is sought, the so-called magnetite. Desired oxidation layer thicknesses are between 0.5 and 2 ⁇ m predominantly corrosive stress, or between 1 and 3 ⁇ m in the case of predominant wear stress.
- the oxide layers are too thick and can flake off. If the oxidation effect of the oxidation atmosphere is set incorrectly, other iron oxide modifications also arise, such as Fe2O3 or FeO. These iron oxide modifications do not improve the corrosion and wear behavior of the workpieces, they can even worsen it. The setting of such iron oxides should therefore be avoided during post-oxidation. The generation of thick Fe3O4 layers can be harmful, especially in the case of corrosion, as practice has shown. The targeted setting of the desired layer modification and thickness setting during post-oxidation is therefore of particular importance.
- the object of the invention is to improve a method for producing uniform oxidation layers of the generic type in such a way that defined, uniform oxidation layers and workpiece surface properties are achieved. Furthermore, an apparatus for performing the method is to be provided.
- the generic method is further developed in that the oxygen potential present in the oxidation atmosphere is continuously determined, the measurement result is compared with a predetermined target value and, in the event of deviations, the oxidation atmosphere is modified until the measurement result matches the target value.
- the setpoint is determined so that the oxygen potential in the oxidation atmosphere at the given oxidation temperature is always just above the formation limit of Fe3O4 oxide, but below the formation limit of the other iron oxides.
- a range between 1100 mV and 800 mV at temperatures from 450 ° C to 650 ° C has proven to be suitable for setting the setpoint of the oxygen potential.
- Air, water, CO2, N2O and the like are advantageously supplied as the oxidizing agent, these oxidizing agents mentioned being able to be supplied individually but also in the context of gas mixtures from these components.
- H2, NH3, CH4 or CO is proposed in an advantageous manner. These components can also be used individually or as a gas mixture.
- a device for post-oxidation after nitrocarburizing or nitriding comprises an atmosphere furnace which has a heating device and at least one gas supply line.
- Known atmosphere furnaces usually have circulation devices which lead the gas forming the atmosphere out of a batch space and back into the batch space along heating devices or heat exchangers.
- the device according to the invention for carrying out the method for producing uniform oxidation layers on metallic workpieces has been further developed in that an oxygen probe is arranged in the area of the batch space of the oxidation atmosphere.
- this oxygen probe can be used to determine the oxygen potential at any time and depending on the time, evaluate the temperature and the like.
- the device according to the invention advantageously has a control device which regulates the gas supply to the atmosphere furnace as a function of the measured value and the predetermined target value.
- the control device acts on valves located in the area of gas supply lines.
- a particularly advantageous device-side solution for regulating the oxygen potential during post-oxidation is characterized by the use of an Endexo retort.
- Such retorts are already known for generating carrier gas in nitrocarburizing furnaces. Endogas are usually produced using the Endexo retort during nitrocarburization.
- the nitrating agent for example ammonia, needs to be switched off.
- the Endexo retort is then carried out in such a way that the natural gas supply is cut off when the setpoint of the oxygen potential falls below the setpoint, or the natural gas supply is switched on again when the setpoint is exceeded while the air supply to the retort remains constant.
- an atmosphere oven 1 known per se, consisting of an oven housing 2 which is arranged on a frame 3. Inside the furnace 1 has a furnace chamber 4 which comprises a batch space 5.
- the atmospheric furnace 1 comprises a gas supply line 8, into which the gases required in each case are fed into the furnace space via corresponding valves.
- the control valve 9a NH3 the control valve 9b, the endogas or exogas, the control valve 9c nitrogen and the control valve 9d air, water or another oxidizing agent.
- an oxygen probe 10 is provided, with which the oxygen potential is measured. The measured value is compared with a desired value by a control device, not shown. If a deviation is found, the respective valves 9a, 9b and 9d can be actuated by the control device 13 in order to modify the oxidation atmosphere in the furnace chamber 4.
- FIG. 2 A corresponding embodiment is shown in FIG. 2.
- the atmosphere furnace 1 is constructed in the manner described.
- the figure shows the use of a so-called endexo retort.
- the oxygen probe 10 shown it is also possible to discharge a so-called sample gas by means of a gas discharge line 12 and to measure outside the atmosphere furnace 1 by means of an oxygen probe ( ⁇ probe), not shown.
- ⁇ probe oxygen probe
- ammonia can be introduced into the furnace via the control valve 9a via a separate feed line 8. This valve remains closed during post-oxidation.
- Natural gas is supplied via the control valve 9b. If the measured oxygen potential value exceeds the target value, the valve 9b is opened. The natural gas supply is switched off when the value falls below the target value. Only oxidizing agent is supplied to the furnace chamber 4 via the oxygen source 11 and the valve 9c.
- the diagram shown in FIG. 3 shows the control range according to the invention, which is to be maintained by the setpoint determination.
- the diagram shows the oxygen probe voltage mV over the temperature in ° C.
- the desired range in which in the oxidation atmosphere at the given oxidation temperature the oxidation is always just above the formation limit of Fe3O4 oxide, but regularly below the formation limit of the other iron oxides, can, as shown in Fig. 3, for example in the temperature range of specify approx. 450 ° C to approx. 650 ° C with an oxygen probe voltage between approx. 1100 mV and 800 mV (hatched area).
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Abstract
Description
Die Erfindung betrifft ein Verfahren zur Herstellung einheitlicher Oxidationsschichten auf metallischen Werkstücken im Anschluß an ein Nitrier- oder Nitrocarburierverfahren, wobei die Werkstücke nach dem Nitrieren oder Nitrocarburieren bei gegebener Temperatur für eine vorgegebene Zeit einer Oxidationsatmosphäre ausgesetzt werden.The invention relates to a process for producing uniform oxidation layers on metallic workpieces following a nitriding or nitrocarburizing process, the workpieces being exposed to an oxidizing atmosphere for a predetermined time after the nitriding or nitrocarburizing at a given temperature.
Die gattungsgemäßen Verfahren werden zur Verbesserung des Verschleiß- bzw. des Korrosionswiderstandes der Oberflächen von Bauteilen aus Eisenwerkstoffen eingesetzt. Dabei wird das Nitrocarburierverfahren als besonderes Nitrierverfahren bei Temperaturen zwischen 570°C und 700°C durchgeführt. Dadurch wird der Verzug geringgehalten. Im Anschluß an das Nitrieren oder Nitrocarburieren werden die Werkstücke einer Oxidationsatmosphäre ausgesetzt. Man spricht von der sogenannten Nachoxidation. Durch die Nachoxidation können der Verschleißwiderstand und insbesondere der Korrosionswiderstand der nitrocarburierten Oberflächen noch erheblich gesteigert werden. Hierzu werden in Atomsphärenöfen die Werkstücke im Anschluß an das Nitrieren bzw. Nitrocarburieren in einer sauerstoffhaltigen Atmosphäre oxidiert. Diese Nachoxidation findet normalerweise bei Temperaturen zwischen 500°C und 550°C statt, ist jedoch auf diesen Bereich nicht festgelegt. Zur Oxidation werden in erster Linie Luft, Wasserdampf, CO₂, Lachgas und Gemische aus diesen Gasen mit Stickstoff oder auch Ammoniak verwendet. Das Ziel der Nachoxidation ist es, die äußere Randschicht der Werkstücke, die im wesentlichen aus Eisennitriden bzw. Carbonitriden besteht, in eine dünne Eisenoxidschicht umzuwandeln. Im Idealfall wird eine Eisenoxidschicht der Form Fe₃O₄ angestrebt, das sogenannte Magnetit. Gewünschte Oxidationsschichtdicken liegen zwischen 0,5 und 2µm bei einer vorwiegend korrosiven Beanspruchung, bzw. zwischen 1 und 3µm im Falle einer vorwiegenden Verschleißbeanspruchung.The generic methods are used to improve the wear and corrosion resistance of the surfaces of components made of ferrous materials. The nitrocarburizing process is carried out as a special nitriding process at temperatures between 570 ° C and 700 ° C. This minimizes the delay. After nitriding or nitrocarburizing, the workpieces are exposed to an oxidation atmosphere. One speaks of the so-called post-oxidation. The post-oxidation can significantly increase the wear resistance and in particular the corrosion resistance of the nitrocarburized surfaces. For this purpose, the workpieces are oxidized in an oxygen-containing atmosphere in an atmosphere-sphere furnace after the nitriding or nitrocarburizing. This post-oxidation normally takes place at temperatures between 500 ° C and 550 ° C, but is not limited to this range. Air, water vapor, CO₂, laughing gas and mixtures of these gases with nitrogen or ammonia are primarily used for the oxidation. The aim of the post-oxidation is to convert the outer edge layer of the workpieces, which essentially consists of iron nitrides or carbonitrides, into a thin iron oxide layer. Ideally, an iron oxide layer of the form Fe₃O₄ is sought, the so-called magnetite. Desired oxidation layer thicknesses are between 0.5 and 2 µm predominantly corrosive stress, or between 1 and 3 µm in the case of predominant wear stress.
Wird zu lang, zu stark oder bei zu hohen Temperaturen oxidiert, so bilden sich zu dicke Oxidschichten, die abplatzen können. Bei falsch eingestellter Oxidationswirkung der Oxidationsatmosphäre entstehen auch andere Eisenoxidmodifikationen, wie beispielsweise das Fe₂O₃ oder das FeO. Diese Eisenoxidmodifikationen verbessern das Korrosions- und Verschleißverhalten der Werkstücke nicht, sondern sie können es sogar verschlechtern. Die Einstellung solcher Eisenoxide ist daher bei der Nachoxidation zu vermeiden. Auch das Erzeugen zu dicker Fe₃O₄-Schichten kann gerade im Fall von Korrosionsbeanspruchung schädlich sein, wie die Praxis gezeigt hat. Die gezielte Einstellung der angestrebten Schichtmodifikation und Dickeneinstellung bei der Nachoxidation ist daher von besonderer Bedeutung.If the oxidation is too long, too strong or at too high temperatures, the oxide layers are too thick and can flake off. If the oxidation effect of the oxidation atmosphere is set incorrectly, other iron oxide modifications also arise, such as Fe₂O₃ or FeO. These iron oxide modifications do not improve the corrosion and wear behavior of the workpieces, they can even worsen it. The setting of such iron oxides should therefore be avoided during post-oxidation. The generation of thick Fe₃O₄ layers can be harmful, especially in the case of corrosion, as practice has shown. The targeted setting of the desired layer modification and thickness setting during post-oxidation is therefore of particular importance.
Es ist im Stand der Technik bekannt, diese Schichtsteuerung über die Oxidationstemperatur und/oder die Oxidationsdauer vorzunehmen. Im HTM 43, 1988, Heft 6, Seite 365 bis 372, ist "NIOX - ein modifiziertes Nitrocarburierverfahren mit anschließender Oxidation" von S. Pakrasi beschrieben. Hier wird eine einzuhaltende Temperatur von 520°C angegeben, in welcher die Werkstücke für eine Stunde lang in Wasserdampf behandelt werden. Gemäß einem anderen Verfahren, dem sogenannten "NITROTEC"-Randschichtbehandlungsverfahren, veröffentlicht von C. Dawes in TZ für Metallbearbeitung, Heft 6, 1984, wird eine Nachoxidation bei 570°C bis 580°C für 30 sec. beschrieben, wobei die Nachoxidation an Luft durchgeführt wird.It is known in the prior art to carry out this layer control via the oxidation temperature and / or the oxidation duration. In HTM 43, 1988,
In der Praxis hat sich gezeigt, daß die Steuerung der Schichtmodifikation und Schichtdicke allein durch die Einstellung der Oxidationstemperatur und/oder der Oxidationsdauer sowie des gewählten Oxidationsmediums, d.h. beispielsweise Luft oder Wasser, nicht ausreicht, um einheitliche Oxidationsschichten und Oberflächeneigenschaften zu garantieren. Je nach Ofen, Werkstückoberflächenzustand und weiteren Faktoren werden unterschiedliche Nachoxidationsergebnisse erzielt. So hat sich gezeigt, daß die Nachoxidation an Luft nicht immer zu einheitlich gefärbten Oberflächen führt. Es können fleckig ausgebildete Oberflächen entstehen, obwohl vorgegebene Oxidationstemperaturen und Oxidationszeiträume eingehalten werden.In practice, it has been shown that the control of the layer modification and layer thickness simply by setting the oxidation temperature and / or the oxidation duration and the chosen oxidation medium, ie for example air or water, is not sufficient to guarantee uniform oxidation layers and surface properties. Depending on the furnace, workpiece surface condition and other factors, different post-oxidation results are achieved. It has been shown that post-oxidation in air does not always lead to uniformly colored surfaces. It can be spotty trained Surfaces arise even though specified oxidation temperatures and oxidation periods are observed.
Davon ausgehend liegt der Erfindung die Aufgabe zugrunde, ein Verfahren zur Herstellung einheitlicher Oxidationsschichten der gattungsgemäßen Art dahingehend zu verbessern, daß definierte, einheitliche Oxidationsschichten und Werkstückoberflächeneigenschaften erzielt werden. Weiterhin soll eine Vorrichtung zur Durchführung des Verfahrens bereitgestellt werden.Proceeding from this, the object of the invention is to improve a method for producing uniform oxidation layers of the generic type in such a way that defined, uniform oxidation layers and workpiece surface properties are achieved. Furthermore, an apparatus for performing the method is to be provided.
Als technische Lösung dieser Aufgabe wird das gattungsgemäße Verfahren dadurch weiterentwickelt, daß das in der Oxidationsatmosphäre vorhandene Sauerstoffpotential ständig bestimmt wird, das Meßergebnis mit einem vorgegebenen Sollwert verglichen und bei Abweichungen die Oxidationsatmosphäre modifiziert wird, bis das Meßergebnis mit dem Sollwert übereinstimmt.As a technical solution to this problem, the generic method is further developed in that the oxygen potential present in the oxidation atmosphere is continuously determined, the measurement result is compared with a predetermined target value and, in the event of deviations, the oxidation atmosphere is modified until the measurement result matches the target value.
Durch die Regelung des Sauerstoffpotentials in der Oxidationsatmosphäre kann sichergestellt werden, daß keine unerwünschten Eisenoxidmodifikationen gebildet werden. Darüber hinaus sind die erzielten Ergebnisse immer einheitlich. Die Oxidschichten haben eine einheitliche Erscheinungsform und die Oberflächeneigenschaften sind definiert und problemlos nachbildbar.By regulating the oxygen potential in the oxidation atmosphere, it can be ensured that no undesirable iron oxide modifications are formed. In addition, the results achieved are always uniform. The oxide layers have a uniform appearance and the surface properties are defined and easily reproducible.
Mit Vorteil wird angegeben, daß der Sollwert so festgelegt wird, daß das Sauerstoffpotential in der Oxidationsatmosphäre bei der gegebenen Oxidationstemperatur immer gerade oberhalb der Entstehungsgrenze von Fe₃O₄-Oxid, aber unterhalb der Entstehungsgrenze der anderen Eisenoxide liegt.Advantageously, it is stated that the setpoint is determined so that the oxygen potential in the oxidation atmosphere at the given oxidation temperature is always just above the formation limit of Fe₃O₄ oxide, but below the formation limit of the other iron oxides.
Für die Einstellung des Sollwertes des Sauerstoffpotentials hat sich ein Bereich zwischen 1100 mV und 800 mV bei Temperaturen von 450°C bis 650°C als geeignet erwiesen.A range between 1100 mV and 800 mV at temperatures from 450 ° C to 650 ° C has proven to be suitable for setting the setpoint of the oxygen potential.
Mit Vorteil wird angegeben, daß dann, wenn das gemessene Sauerstoffpotential unterhalb des vorgegebenen Sollwertes liegt, weiteres Oxidationsmittel zugeführt wird. Liegt der gemessene Sauerstoffpotentialwert oberhalb des vorgegebenen Sollwertes, so wird gemäß einem Vorschlag der Erfindung die Zufuhr des Oxidationsmittels gestoppt. Alternativ oder zusätzlich kann der Oxidationsatmosphäre auch ein Reduktionsmittel zugeführt werden.Advantageously, it is stated that when the measured oxygen potential is below the predetermined target value, further oxidizing agent is added. If the measured oxygen potential value lies above the predetermined target value, then according to a proposal of the invention the supply of the oxidant stopped. Alternatively or additionally, a reducing agent can also be added to the oxidation atmosphere.
Auch sind Kombinationen der vorgeschlagenen Maßnahmen im Rahmen der Erfindung möglich. Gemäß einem Vorschlag der Erfindung wird bei Sollwertüberschreitungen die Oxidationsmittelwegschaltung und die Reduktionsmittelzuschaltung sowohl gleichzeitig als auch im Wechsel vorgenommen. Bei einer Sollwertunterschreitung wird gemäß einem Vorschlag der Erfindung die Oxidationsmittelzuschaltung und die Reduktionsmittelwegschaltung ebenfalls sowohl gleichzeitig als auch im Wechsel vorgenommen.Combinations of the proposed measures are also possible within the scope of the invention. According to a proposal of the invention, if the setpoint is exceeded, the oxidant cut-out and the reductant cut-in are carried out both simultaneously and alternately. If the value falls below the target value, the oxidant connection and the reducing agent path connection are likewise carried out both simultaneously and alternately according to a proposal of the invention.
Als Oxidationsmittel wird in vorteilhafter Weise Luft, Wasser, CO₂, N₂O und dergleichen zugeführt, wobei diese genannten Oxidationsmittel einzeln aber auch im Rahmen von Gasmischungen aus diesen Komponenten zugeführt werden können.Air, water, CO₂, N₂O and the like are advantageously supplied as the oxidizing agent, these oxidizing agents mentioned being able to be supplied individually but also in the context of gas mixtures from these components.
Als Reduktionsmittel wird in vorteilhafter Weise H₂, NH₃, CH₄ oder CO vorgeschlagen. Auch diese Komponenten können einzeln oder als Gasmischung verwendet werden.As a reducing agent, H₂, NH₃, CH₄ or CO is proposed in an advantageous manner. These components can also be used individually or as a gas mixture.
Vorrichtungsseitig umfaßt eine Vorrichtung zur Nachoxidation nach dem Nitrocarburieren bzw. Nitrieren einen Atmosphärenofen, der eine Heizvorrichtung und wenigstens eine Gaszuführleitung aufweist. Üblicherweise weisen bekannte Atmosphärenöfen Umwälzvorrichtungen auf, welche das die Atmosphäre bildende Gas aus einem Chargenraum heraus, und entlang von Heizeinrichtungen oder Wärmetauschern wieder in den Chargenraum zurückführen.On the device side, a device for post-oxidation after nitrocarburizing or nitriding comprises an atmosphere furnace which has a heating device and at least one gas supply line. Known atmosphere furnaces usually have circulation devices which lead the gas forming the atmosphere out of a batch space and back into the batch space along heating devices or heat exchangers.
Die erfindungsgemäße Vorrichtung zur Durchführung des Verfahrens zur Herstellung einheitlicher Oxidationsschichten auf metallischen Werkstücken ist dadurch weiterentwickelt, daß im Bereich des Chargenraumes der Oxidationsatmosphäre eine Sauerstoffsonde angeordnet ist.The device according to the invention for carrying out the method for producing uniform oxidation layers on metallic workpieces has been further developed in that an oxygen probe is arranged in the area of the batch space of the oxidation atmosphere.
Mit dieser Sauerstoffsonde läßt sich verfahrensgemäß das Sauerstoffpotential zu jedem beliebigen Zeitpunkt bestimmten und in Abhängigkeit von der Zeit, der Temperatur und dgl. auswerten. In vorteilhafter Weise weist die erfindungsgemäße Vorrichtung eine Steuereinrichtung auf, welche in Abhängigkeit von dem Meßwert und dem vorgegebenen Sollwert die Gaszufuhr zum Atmosphärenofen regelt. Gemäß einer vorteilhaften Ausgestaltung der Erfindung wirkt die Steuereinrichtung auf im Bereich von Gaszuführleitungen liegende Ventile ein.According to the method, this oxygen probe can be used to determine the oxygen potential at any time and depending on the time, evaluate the temperature and the like. The device according to the invention advantageously has a control device which regulates the gas supply to the atmosphere furnace as a function of the measured value and the predetermined target value. According to an advantageous embodiment of the invention, the control device acts on valves located in the area of gas supply lines.
Eine besonders vorteilhafte vorrichtungsseitige Lösung zur Regelung des Sauerstoffpotentials während der Nachoxidation ist durch den Einsatz einer Endexo-Retorte gekennzeichnet. Derartige Retorten sind zur Erzeugung von Trägergas bei Nitrocarburieröfen bereits bekannt. Mittels der Endexo-Retorte wird üblicherweise während der Nitrocarburierung Endogas hergestellt. Um die Endexo-Retorte für die Nachoxidation zu verwenden, braucht dann nur das Nitriermittel, beispielsweise das Ammoniak, abgeschaltet zu werden. Die Endexo-Retorte wird dann so geführt, daß bei Unterschreiten des Sollwertes des Sauerstoffpotentials in der Oxidationsatmosphäre die Erdgaszufuhr weggeschaltet, bzw. bei Überschreiten des Sollwertes die Erdgaszufuhr wieder zugeschaltet wird bei konstant bleibender Luftzuführung zur Retorte.A particularly advantageous device-side solution for regulating the oxygen potential during post-oxidation is characterized by the use of an Endexo retort. Such retorts are already known for generating carrier gas in nitrocarburizing furnaces. Endogas are usually produced using the Endexo retort during nitrocarburization. To use the Endexo retort for post-oxidation, only the nitrating agent, for example ammonia, needs to be switched off. The Endexo retort is then carried out in such a way that the natural gas supply is cut off when the setpoint of the oxygen potential falls below the setpoint, or the natural gas supply is switched on again when the setpoint is exceeded while the air supply to the retort remains constant.
Weitere Vorteile und Merkmale der Erfindung ergeben sich aus der folgenden Beschreibung anhand der Figuren. Dabei zeigen:
- Fig. 1
- eine schematische Darstellung einer erfindungsgemäßen Vorrichtung zur Durchführung des erfindungsgemäßen Nachoxidationsverfahrens;
- Fig. 2
- eine schematische Darstellung eines weiteren Ausführungsbeispieles einer Vorrichtung zur Durchführung des erfindungsgemäßen Nachoxidationsverfahrens und
- Fig. 3
- ein Schaubild zur Darstellung des angestrebten Regelbereiches.
- Fig. 1
- a schematic representation of a device according to the invention for performing the post-oxidation process according to the invention;
- Fig. 2
- is a schematic representation of a further embodiment of a device for performing the post-oxidation process according to the invention and
- Fig. 3
- a diagram to show the desired control range.
In Fig. 1 ist ein an sich bekannter Atmosphärenofen 1 gezeigt, bestehend aus einem Ofengehäuse 2, welches auf einem Gestell 3 angeordnet ist. Im Inneren weist der Ofen 1 eine Ofenkammer 4 auf, welche einen Chargenraum 5 umfaßt. Ein Umwälzgebläse 6, welches von einem thermisch isolierten Antrieb 7 angetrieben wird, saugt aus dem Chargenraum das Atmosphärengas ab und wälzt es in den die Ofenkammer umgebenden Raum, in welchem nicht gezeigte Heizelemente angeordnet sind. Das Gas tritt dann mit der richtigen Temperatur wieder von unten in den Chargenraum 5 ein.1 shows an atmosphere oven 1 known per se, consisting of an
Der Atmosphärenofen 1 umfaßt eine Gaszufuhrleitung 8, in welche über entsprechende Ventile die jeweils erforderlichen Gase in den Ofenraum geführt werden. So kann beispielsweise über das Regelventil 9a NH₃, über das Regelventil 9b das Endo- bzw. Exogas, über das Regelventil 9c Stickstoff und über das Regelventil 9d Luft, Wasser oder ein sonstiges Oxidationsmittel zugeführt werden.The atmospheric furnace 1 comprises a
Zur Ermittlung des Sauerstoffpotentiales in der Ofenkammer 4 ist eine Sauerstoffsonde 10 vorgesehen, mit welcher das Sauerstoffpotential gemessen wird. Von einer nicht gezeigten Steuervorrichtung wird der Meßwert mit einem Sollwert verglichen. Wird eine Abweichung festgestellt, können von der Steuervorrichtung 13 die jeweiligen Ventile 9a, 9b und 9d angesteuert werden, um die Oxidationsatmosphäre in der Ofenkammer 4 zu modifizieren.To determine the oxygen potential in the furnace chamber 4, an
Eine entsprechende Ausführungsform ist in Fig. 2 gezeigt. Der Atmosphärenofen 1 ist in der beschriebenen Weise aufgebaut. Die Figur zeigt die Verwendung einer sogenannten Endexo-Retorte. Anstelle der gezeigten Sauerstoffsonde 10 ist auch möglich, mittels einer Gasabführleitung 12 ein sogenanntes Probegas abzuführen und außerhalb des Atmosphärenofens 1 mittels einer nicht gezeigten Sauerstoffsonde (λ-Sonde) zu messen. Über das Regelventil 9a kann beispielsweise Ammoniak über eine gesonderte Zuführleitung 8 in den Ofen eingebracht werden. Während der Nachoxidation bleibt dieses Ventil geschlossen. Über das Stellventil 9b wird Erdgas zugeführt. Überschreitet der gemessene Sauerstoffpotentialwert den Sollwert, wird das Ventil 9b geöffnet. Bei Unterschreiten des Sollwertes wird die Erdgaszufuhr weggeschaltet. Über die Sauerstoffquelle 11 und das Ventil 9c wird nur Oxidationsmittel der Ofenkammer 4 zugeführt.A corresponding embodiment is shown in FIG. 2. The atmosphere furnace 1 is constructed in the manner described. The figure shows the use of a so-called endexo retort. Instead of the
Das in der Figur 3 gezeigte Schaubild zeigt den erfindungsgemäßen Regelbereich, welcher durch die Sollwertfestlegung eingehalten werden soll. Das Schaubild zeigt die Sauerstoffsondenspannung mV über der Temperatur in °C. Der gewünschte Bereich, bei welchem in der Oxidationsatmosphäre bei der gegebenen Oxidationstemperatur die Oxidation immer gerade oberhalb der Enstehungsgrenze von Fe₃O₄-Oxid, aber regelmäßig unterhalb der Entstehungsgrenze der anderen Eisenoxide liegt, läßt sich, wie in Fig. 3 gezeigt, beispielsweise in dem Temperaturbereich von etwa 450°C bis etwa 650°C mit einer Sauerstoffsondenspannung zwischen etwa 1100 mV und 800 mV (schraffierter Bereich) angeben.The diagram shown in FIG. 3 shows the control range according to the invention, which is to be maintained by the setpoint determination. The diagram shows the oxygen probe voltage mV over the temperature in ° C. The desired range, in which in the oxidation atmosphere at the given oxidation temperature the oxidation is always just above the formation limit of Fe₃O₄ oxide, but regularly below the formation limit of the other iron oxides, can, as shown in Fig. 3, for example in the temperature range of specify approx. 450 ° C to approx. 650 ° C with an oxygen probe voltage between approx. 1100 mV and 800 mV (hatched area).
- 11
- AtmosphärenofenAtmospheric furnace
- 22nd
- Gehäusecasing
- 33rd
- Gestellframe
- 44th
- OfenkammerFurnace chamber
- 55
- ChargenraumBatch room
- 66
- UmwälzgebläseCirculation blowers
- 77
- Antriebdrive
- 88th
- GaszufuhrleitungGas supply line
- 9a9a
- VentilValve
- 9b9b
- VentilValve
- 9c9c
- VentilValve
- 9d9d
- VentilValve
- 1010th
- SauerstoffsondeOxygen probe
- 1111
- SauerstoffquelleOxygen source
- 1212th
- GasabführleitungGas discharge line
- 1313
- SteuervorrichtungControl device
Claims (15)
dadurch gekennzeichnet,
daß das in der Oxidationsatmosphäre vorhandene Sauerstoffpotential ständig bestimmt wird, das Meßergebnis mit einem vorgegebenen Sollwert verglichen und bei Abweichungen die Oxidationsatmosphäre modifiziert wird, bis das Meßergebnis mit dem Sollwert übereinstimmt.Process for producing uniform oxidation layers on metallic workpieces following a nitriding or nitrocarburizing process, the workpieces being exposed to an oxidizing atmosphere for a predetermined time after nitriding or nitrocarburizing at a given temperature,
characterized by
that the oxygen potential present in the oxidation atmosphere is continuously determined, the measurement result is compared with a predetermined target value and, in the event of deviations, the oxidation atmosphere is modified until the measurement result matches the target value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4339404 | 1993-11-18 | ||
| DE4339404A DE4339404A1 (en) | 1993-11-18 | 1993-11-18 | Process for producing uniform oxidation layers on metallic workpieces and device for carrying out the process |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0655512A1 true EP0655512A1 (en) | 1995-05-31 |
| EP0655512B1 EP0655512B1 (en) | 2000-07-19 |
Family
ID=6502908
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP94116881A Expired - Lifetime EP0655512B1 (en) | 1993-11-18 | 1994-10-26 | Method for producing unitary oxidic layers on metallic substrates and apparatus for carrying out the process |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0655512B1 (en) |
| AT (1) | ATE194855T1 (en) |
| DE (2) | DE4339404A1 (en) |
| ES (1) | ES2149835T3 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1122331A1 (en) * | 2000-02-04 | 2001-08-08 | Ipsen International GmbH | Process of nitriding and/or carbonitriding of high-alloyed steel |
| WO2003052158A1 (en) * | 2001-12-18 | 2003-06-26 | Messer Griesheim Gmbh | Method for producing an oxide layer on metallic elements |
| US7160576B2 (en) | 2002-08-01 | 2007-01-09 | Ipsen International Gmbh | Method and device for blacking components |
| WO2007009521A1 (en) * | 2005-07-22 | 2007-01-25 | Iwis Motorsysteme Gmbh & Co. Kg | Link chain having nitrided bearing face with oxidation coating |
| ITMI20110366A1 (en) * | 2011-03-10 | 2012-09-11 | Sol Spa | PROCEDURE FOR STEEL TREATMENT. |
| WO2023104385A1 (en) * | 2021-12-07 | 2023-06-15 | Robert Bosch Gmbh | Method and device for the localised nitriding or nitrocarburising of the surface of a component |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19938009C1 (en) * | 1999-08-11 | 2000-10-26 | Ipsen Ind Int Gmbh | Device for heat treating metallic workpieces comprises a heat-resistant lined furnace chamber that is divided into a region of reduced cross-section leading into first treatment zone |
| DE102015204656A1 (en) * | 2015-03-16 | 2016-09-22 | Aktiebolaget Skf | Layer formation for rolling bearing components |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2114603A (en) * | 1982-02-02 | 1983-08-24 | Cabot Corp | Method of heat treating nicraly alloys for use as ceramic kiln and furnace hardware |
| EP0122762A1 (en) * | 1983-04-14 | 1984-10-24 | LUCAS INDUSTRIES public limited company | Corrosion resistant steel components and method of manufacture thereof |
| GB2159542A (en) * | 1984-05-25 | 1985-12-04 | Maschf Augsburg Nuernberg Ag | Method for producing protective oxidic layers on metallic surfaces |
| DE3935469A1 (en) * | 1988-12-22 | 1990-06-28 | Thaelmann Schwermaschbau Veb | Gas oxy:nitriding ferrous components - by controlling oxygen-potential and concn. of ammonia, nitrogen, hydrogen and water as well as dissociated ammonia |
-
1993
- 1993-11-18 DE DE4339404A patent/DE4339404A1/en not_active Withdrawn
-
1994
- 1994-10-26 EP EP94116881A patent/EP0655512B1/en not_active Expired - Lifetime
- 1994-10-26 AT AT94116881T patent/ATE194855T1/en active
- 1994-10-26 DE DE59409455T patent/DE59409455D1/en not_active Expired - Lifetime
- 1994-10-26 ES ES94116881T patent/ES2149835T3/en not_active Expired - Lifetime
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2114603A (en) * | 1982-02-02 | 1983-08-24 | Cabot Corp | Method of heat treating nicraly alloys for use as ceramic kiln and furnace hardware |
| EP0122762A1 (en) * | 1983-04-14 | 1984-10-24 | LUCAS INDUSTRIES public limited company | Corrosion resistant steel components and method of manufacture thereof |
| GB2159542A (en) * | 1984-05-25 | 1985-12-04 | Maschf Augsburg Nuernberg Ag | Method for producing protective oxidic layers on metallic surfaces |
| DE3935469A1 (en) * | 1988-12-22 | 1990-06-28 | Thaelmann Schwermaschbau Veb | Gas oxy:nitriding ferrous components - by controlling oxygen-potential and concn. of ammonia, nitrogen, hydrogen and water as well as dissociated ammonia |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1122331A1 (en) * | 2000-02-04 | 2001-08-08 | Ipsen International GmbH | Process of nitriding and/or carbonitriding of high-alloyed steel |
| WO2003052158A1 (en) * | 2001-12-18 | 2003-06-26 | Messer Griesheim Gmbh | Method for producing an oxide layer on metallic elements |
| CN1322161C (en) * | 2001-12-18 | 2007-06-20 | 梅塞尔集团有限公司 | Method for producing an oxide layer on metallic elements |
| US7160576B2 (en) | 2002-08-01 | 2007-01-09 | Ipsen International Gmbh | Method and device for blacking components |
| WO2007009521A1 (en) * | 2005-07-22 | 2007-01-25 | Iwis Motorsysteme Gmbh & Co. Kg | Link chain having nitrided bearing face with oxidation coating |
| ITMI20110366A1 (en) * | 2011-03-10 | 2012-09-11 | Sol Spa | PROCEDURE FOR STEEL TREATMENT. |
| EP2497839A1 (en) * | 2011-03-10 | 2012-09-12 | SOL S.p.A. | Method for the treatment of steels |
| WO2023104385A1 (en) * | 2021-12-07 | 2023-06-15 | Robert Bosch Gmbh | Method and device for the localised nitriding or nitrocarburising of the surface of a component |
Also Published As
| Publication number | Publication date |
|---|---|
| DE59409455D1 (en) | 2000-08-24 |
| ATE194855T1 (en) | 2000-08-15 |
| EP0655512B1 (en) | 2000-07-19 |
| ES2149835T3 (en) | 2000-11-16 |
| DE4339404A1 (en) | 1995-05-24 |
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