EP1160349B1 - Process and apparatus for heat treating of metallic workpieces - Google Patents
Process and apparatus for heat treating of metallic workpieces Download PDFInfo
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- EP1160349B1 EP1160349B1 EP00111129A EP00111129A EP1160349B1 EP 1160349 B1 EP1160349 B1 EP 1160349B1 EP 00111129 A EP00111129 A EP 00111129A EP 00111129 A EP00111129 A EP 00111129A EP 1160349 B1 EP1160349 B1 EP 1160349B1
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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
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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
- C23C8/28—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 one step
- C23C8/30—Carbo-nitriding
- C23C8/32—Carbo-nitriding of ferrous surfaces
Definitions
- the invention relates to a method for heat treatment of metallic Workpieces, especially for carburizing or carbonitriding Ferrous materials. It also relates to a device with which one can carry out such procedure.
- thermochemical heat treatment To create defined workpiece properties, such as a high one Wear or alternating strength, metallic workpieces become one subjected to thermochemical heat treatment.
- the result of Heat treatment is the enrichment of carburizing or carbonitriding Surface layer of the workpieces with carbon and / or nitrogen, due to the changed material composition of the workpieces after a subsequent hardening to give the required mechanical properties.
- the treatment result is of particular influence general process parameters pressure, temperature and duration of treatment in primarily the composition of the enrichment of the boundary layer Carbon and / or nitrogen causing gas atmosphere. It can be about be required to add a reducing agent to the gas atmosphere in order to obtain a impermissibly high oxidation of the surface of the workpieces due to the Loading the workpieces in a heat treatment furnace due to the to avoid inevitable air intake noticeable oxygen.
- the prior art also includes a number of procedures known to the composition of the gas atmosphere in terms of to adjust the desired treatment outcome.
- the gas atmosphere is in Depending on the carburizing temperature in its carburizing effect on the adapt to the respective requirements.
- This is a common practice So-called saturation compensation method, in which during a Enrichment phase the maximum possible amount of carbon in the Gas atmosphere is provided to saturate the surface layer with Reach carbon in a short time.
- the exchange of substances with the gas atmosphere restricted or prevented by either using a gas atmosphere reduced carbon supply set or the gas atmosphere evacuated or is exchanged for an inert gas.
- EP-A-0 080 124 describes a case hardening process known metallic workpieces, in which by pulsating addition carbon-containing gas components achieved a high carbon potential gradient becomes. The supply of the carbon-containing gas takes place in several cycles instead of and is interrupted as soon as saturation occurs in the boundary layer Carbon is reached.
- GB-A-2 202 238 discloses a method for Carburizing workpieces, in which the enrichment phase and the Diffusion phase periodically until a desired carburization depth is reached alternate to the desired carbon content of the surface layer and the target carburization depth largely independent of each other and in to achieve as short a time as possible.
- a method and a device for thermal or thermomechanical Treatment of steel is also known from US 5,139,584.
- a two-step treatment process which is as follows is carried out: A first phase at possible maximum temperature, defined based on metallurgical criteria, with control of the entry quantity of Hydrocarbons to get a maximum concentration of carbons on the surface, this maximum concentration being at least equal to that Saturation concentration of carbon of austenite; a second phase at the possible maximum temperature, defined based on metallurgical Criteria during which the carbon flow is transferred from the gas phase is zero is the carbon concentration profile and in particular the Set the concentration on the surface to a predetermined value, the is chosen based on metallurgical reasons.
- a disadvantage of all these methods is that they are not always satisfactory Treatment outcome. This is mainly due to the fact that during a diffusion phase following the enrichment phase or Temperature compensation phase no longer has any direct influence on the There is carbon content in the surface layer. This comes in particular Dimensions to be taken into account when there are small amounts of carbon dioxide or Water vapor are in the gas atmosphere, for example due to a Air entry at leaks of a heat treatment furnace are formed and the cause an increased degradation of the carbon in the surface layer. About that also contain those used to regulate carbon levels during the Process gases used in the enrichment phase oxygen-containing components, such as carbon monoxide, carbon dioxide or Water vapor due to the partial pressure of oxygen in the outside Edge area of the carburized edge layer an undesirable edge oxidation cause.
- the invention has for its object to provide a method and an apparatus for the heat treatment of metallic workpieces with which an improved treatment result can be achieved in a comparatively simple manner while avoiding carbide formation on the surface of the workpieces to be treated.
- Such a procedure adopts the knowledge that one can achieve improved treatment results of the workpieces if both during the enrichment phase and during the diffusion phase the carbon content of the boundary layer by varying that of the gas atmosphere supplied volume flows of nitrogen and hydrocarbon in one predetermined interval between a lower limit and an upper limit is set.
- Nitrogen is reduced and the proportion of hydrocarbon is increased high carbon supply in the gas atmosphere, which in a relatively short Time the carbon content of the boundary layer up to the specified upper limit accumulates.
- the temperature to which heating takes place in the heating phase, the length of time for which the workpieces are kept at this temperature during the compensation phase, the temperatures which are set in the enrichment phase and the diffusion phase, and the amounts of nitrogen supplied in the respective process stages and carbon depend primarily on the material of the workpieces to be treated, the specific composition of the gas atmosphere required to achieve the desired carbon content of the surface layer and the desired treatment success, such as the desired carburization depth. Since the process parameters of the material properties depend on the workpieces to be treated, can be obtained from publicly available databases, such as the Calphad (Cal culation of pha se d iagrams), Sweden, necessary for a particular steel composition parameter values with respect to the desired carbon content in the Remove surface layer.
- the amounts of nitrogen and Hydrocarbon in the gas atmosphere during the enrichment phase and / or the diffusion phase advantageously varies such that the Upper limit of the carbon content of the surface layer slightly below the due to carbide formation occurring at the prevailing temperature marked saturation of austenite.
- the upper limit of Carbon content of the surface layer can be so during the diffusion phase be chosen to meet the requirements of one of the following Cooling phase taking place corresponds to the hardening process.
- a particularly advantageous procedure is also given if the workpieces during the heating phase to one for carburizing or Carbonitriding favorable temperature between 750 ° C and 1050 ° C to be heated.
- a carbon content of the surface layer is also of particular advantage during the heating phase in the range between 0.2 wt .-% and 0.5 wt .-%. Possibly existing oxide or passive layers on the workpieces are eliminated in this way or at least converted so that a uniform diffusion of carbon into the material is favored.
- corresponding procedure management also a reduced temperature during the enrichment phase during the diffusion phase be useful.
- a particularly advantageous procedure is also given when unsaturated hydrocarbons of the type C n H 2n , preferably alkenes such as ethylene (C 2 H 4 ) and propylene (C 3 H 6 ), saturated hydrocarbons of the type C n H 2n + 2 , preferably alkanes such as ethane (C 2 H 6 ) and propane (C 3 H 8 ), or alkynes such as acetylene (C 2 H 2 ) are added to the gas atmosphere.
- alkynes which are characterized by a low proportion of hydrogen, offer the advantage that no further fission products are generated and the proportion of hydrogen in the gas atmosphere accordingly remains low.
- a reducing agent preferably hydrogen
- oxygen present in the gas atmosphere which stems, for example, from an air inlet at leaks in a heat treatment furnace constant or variable amount added.
- the point in time and the amount of reducing agent added depend on the prevailing circumstances.
- the supply of the amounts of nitrogen and hydrocarbon into the gas atmosphere is regulated or controlled in a database-dependent manner as a function of a characteristic value representing the carbon content in the surface layer, preferably the carbonation index K c .
- the database-related control is advantageous if a characteristic value representing the carbon content in the surface layer is not available, for example due to measurement difficulties.
- the regulation of the supply as a function of a characteristic value representing the carbon content in the surface layer enables the desired carbon content of the surface layer to be set precisely, without the size of the surface of the workpieces to be treated being particularly important.
- the workpieces are expediently removed during the cooling phase a reducing or neutral gas atmosphere or in a liquid Quench medium cooled to room temperature.
- a device for heat treatment of metallic workpieces which has a heating chamber in which the workpieces can be heated and exposed to a gas atmosphere containing nitrogen and a hydrocarbon, and is characterized in that means are provided with which the supply of the Amounts of nitrogen and hydrocarbon in the gas atmosphere as a function of a characteristic value representing the carbon content in the boundary layer, preferably the carbon index K c , can be regulated or controlled in a database-related manner, with a means arranged within the heating chamber as a means of measuring the characteristic value representing the carbon content in the boundary layer Wire sensor is provided, and that means are provided with which the supply of the amount of a reducing agent, preferably hydrogen, and / or ammonia can be regulated or controlled in a database-related manner.
- the method according to the invention can be carried out in a reliable manner with such a device.
- the Heating chamber is hermetically sealed to prevent air from entering and thus avoid oxygen in the gas atmosphere.
- the heating chamber be filled with an inert gas, preferably nitrogen, is flushable, so that regardless of the volume of the heating chamber the content of Oxygen in the atmosphere of the heating chamber after introduction of the treating workpieces in a comparatively short time to ⁇ 1% by volume reducible and undesirable oxidation of the workpieces to be treated this is avoidable.
- the heat treatment method shown in Fig. 1 is primarily used for carburizing metallic workpieces, which can consist of different steels. The entire process can be divided into five phases. In a first phase, the heating phase A, the workpieces are heated to a carburizing temperature ⁇ of, for example, 930 ° C.
- the heat treatment furnace used for this purpose an atmosphere furnace, was flushed with nitrogen in a short time after the workpieces had been introduced, and was then flooded with a gas atmosphere containing nitrogen and acetylene.
- the size of the volume flows of nitrogen V ⁇ N supplied to the gas atmosphere 2 and acetylene V ⁇ C 2 H 2 is such that an edge layer with a carbon content w c of approx. 0.35% by weight is obtained on the workpieces.
- the supply of the amounts of nitrogen V ⁇ N 2 and acetylene V ⁇ C 2 H 2 The gas atmosphere is regulated as a function of a characteristic value representing the carbon content w c in the surface layer, which is determined by a measuring device.
- the gas atmosphere becomes a constant volume flow of hydrogen V ⁇ H during the heating phase A. 2 of approx. 0.3 m 3 / h to put the gas atmosphere in a sufficiently reducing state.
- a compensation phase B following the heating-up phase A the workpieces are kept at the temperature ⁇ reached at the end of the heating-up phase A of approx. 930 ° C. for approx. 20 min.
- the quantities of nitrogen V ⁇ N fed into the gas atmosphere 2 and acetylene V ⁇ C 2 H 2 are further regulated so that there is a carbon content w c in the surface layer of the workpieces of approx. 0.35% by weight.
- the volume flow of hydrogen V ⁇ H 2 is, however, reduced to a value of less than 0.2 m 3 / h.
- the volume flows of nitrogen V ⁇ N supplied to the gas atmosphere become 2 and acetylene V ⁇ C 2 H 2 varies in such a way that a carbon content w c of the surface layer - occurs in an interval between a lower limit G u of approximately 0.7% by weight and an upper limit G o of approximately 1.2% by weight.
- the upper limit G o of approx. 1.2% by weight is below the saturation limit of austenite which is characterized by carbide and soot formation for unalloyed case-hardened steels.
- the volume flow of nitrogen V ⁇ N 2 reduced and the volume flow of acetylene V ⁇ C 2 H 2 elevated.
- the volume flow of nitrogen V ⁇ N is reached in a second section in order to reach the lower limit G u 2 increased again, whereas the volume flow of acetylene V ⁇ C 2 H 2 is reduced.
- the first and second sections are repeated alternately within the enrichment phase C, whereby an adaptation of the enrichment of the surface layer with carbon is achieved in accordance with the absorption capacity of the workpieces depending on the respective material.
- the duration and thus the respective size of the volume flows of nitrogen is V ⁇ N 2 and acetylene V ⁇ C 2 H 2 during the first and second sections unevenly, as can be seen from the steep slopes of the curve of the carbon content w c in FIG. 1.
- the system and process-adapted volume flow of hydrogen V ⁇ H 2 is increased to approximately 0.2 m 3 / h during the enrichment phase C.
- the enrichment phase C is followed by a diffusion phase D in which the temperature ⁇ is reduced to approximately 880 ° C. With regard to a subsequent hardening process, the upper limit G o is reduced to approximately 0.8% by weight.
- the thermodynamic equilibrium between the gas atmosphere and the boundary layer of the workpieces to be treated is varied by varying the volume flows of nitrogen V ⁇ N supplied to the gas atmosphere 2 and acetylene V ⁇ C 2 H 2 set in first and second sections such that the carbon content w c of the boundary layer lies in the interval between the lower limit G u of approximately 0.7% by weight and the upper limit G o of approximately 0.8% by weight.
- the system and process-adapted volume flow of hydrogen V ⁇ H 2 is again reduced to a value below 0.2 m 3 / h during the diffusion phase D.
- the workpieces are cooled to room temperature during a cooling phase E following the diffusion phase D.
- ammonia V ⁇ NH can additionally be present in the gas atmosphere during the enrichment phase C and the diffusion phase D, as can be seen in FIG. 1 3 are supplied, the amount of ammonia supplied V ⁇ NH 3 in the order of 2 vol.% to 20 vol.% of the total gassing rate.
- the method described above is characterized by the volume flow regulation of the quantities of nitrogen V ⁇ N supplied to the gas atmosphere 2 and acetylene V ⁇ C 2 H 2 in the individual stages of the process, whereby an improved treatment result is achieved in comparison with conventional carburizing processes.
- the main reason for this is that the carbon supply in the gas atmosphere can be adapted in this way according to the material and the surface of the workpieces to be treated and thus the absorption capacity of the surface layer.
- the possibility to provide alternating first and second sections of different carbon contents w c during the enrichment phase C and the diffusion phase D also contributes to this result to a particular extent.
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Abstract
Description
Die Erfindung betrifft ein Verfahren zur Wärmebehandlung metallischer Werkstücke, insbesondere zum Aufkohlen oder Carbonitrieren von Eisenwerkstoffen. Sie bezieht sich ferner auf eine Vorrichtung, mit der sich ein solches Verfahren durchführen lässt.The invention relates to a method for heat treatment of metallic Workpieces, especially for carburizing or carbonitriding Ferrous materials. It also relates to a device with which one can carry out such procedure.
Zum Erzeugen von definierten Werkstückeigenschaften, wie etwa einer hohen Verschleiß- oder Wechselfestigkeit, werden metallische Werkstücke einer thermochemischen Wärmebehandlung unterzogen. Das Ergebnis der Wärmebehandlung ist beim Aufkohlen oder Carbonitrieren die Anreicherung der Randschicht der Werkstücke mit Kohlenstoff und/oder Stickstoff, um aufgrund der veränderten Werkstoffzusammensetzung den Werkstücken nach einem anschließenden Härten die geforderten mechanischen Eigenschaften zu verleihen.To create defined workpiece properties, such as a high one Wear or alternating strength, metallic workpieces become one subjected to thermochemical heat treatment. The result of Heat treatment is the enrichment of carburizing or carbonitriding Surface layer of the workpieces with carbon and / or nitrogen, due to the changed material composition of the workpieces after a subsequent hardening to give the required mechanical properties.
Von besonderem Einfluss auf das Behandlungsergebnis ist neben den allgemeinen Prozessparametem Druck, Temperatur und Behandlungsdauer in erster Linie die Zusammensetzung einer die Anreicherung der Randschicht mit Kohlenstoff und/oder Stickstoff bewirkenden Gasatmosphäre. So kann es etwa erforderlich sein, der Gasatmosphäre ein Reduktionsmittel beizugeben, um eine unzulässig hohe Oxidation der Oberfläche der Werkstücke durch den sich beim Beladen der Werkstücke in einen Wärmebehandlungsofen aufgrund des unvermeidlichen Lufteintritts bemerkbar machenden Sauerstoff zu vermeiden.In addition to the, the treatment result is of particular influence general process parameters pressure, temperature and duration of treatment in primarily the composition of the enrichment of the boundary layer Carbon and / or nitrogen causing gas atmosphere. It can be about be required to add a reducing agent to the gas atmosphere in order to obtain a impermissibly high oxidation of the surface of the workpieces due to the Loading the workpieces in a heat treatment furnace due to the to avoid inevitable air intake noticeable oxygen.
Im Stand der Technik sind darüber hinaus eine Reihe von Verfahrensweisen bekannt, um die Zusammensetzung der Gasatmosphäre in Hinsicht auf das angestrebte Behandlungsergebnis anzupassen. Die Gasatmosphäre ist dabei in Abhängigkeit von der Aufkohlungstemperatur in ihrer Aufkohlungswirkung an die jeweiligen Erfordernisse anzupassen. Eine übliche Verfahrensweise ist das sogenannte Sättigungs-Ausgleichs-Verfahren, bei dem während einer Anreicherungsphase die maximal mögliche Kohlenstoffmenge in der Gasatmosphäre bereitgestellt wird, um eine Sättigung der Randschicht mit Kohlenstoff in kurzer Zeit zu erreichen. Zum Erhalt des gewünschten Kohlenstoffgehalts in der Randschicht wird dann während einer sich anschließenden Diffusionsphase der Stoffaustausch mit der Gasatmosphäre eingeschränkt oder unterbunden, indem entweder eine Gasatmosphäre mit herabgesetztem Kohlenstoffangebot eingestellt oder die Gasatmosphäre evakuiert beziehungsweise gegen ein Inertgas ausgetauscht wird.The prior art also includes a number of procedures known to the composition of the gas atmosphere in terms of to adjust the desired treatment outcome. The gas atmosphere is in Depending on the carburizing temperature in its carburizing effect on the adapt to the respective requirements. This is a common practice So-called saturation compensation method, in which during a Enrichment phase the maximum possible amount of carbon in the Gas atmosphere is provided to saturate the surface layer with Reach carbon in a short time. To get the one you want Carbon content in the boundary layer will then increase during one subsequent diffusion phase, the exchange of substances with the gas atmosphere restricted or prevented by either using a gas atmosphere reduced carbon supply set or the gas atmosphere evacuated or is exchanged for an inert gas.
Ein hierauf basierendes Verfahren offenbart die DE-A-31 39 622, wobei die Anreicherungsphase dabei durch unterschiedliche Regelung des Kohlenstoffpegels der Gasatmosphäre in eine erste und eine zweite Periode unterteilt ist. Während der ersten Periode wird das maximal mögliche Kohlenstoffpotentialgefälle zwischen Gasatmosphäre und der Randschicht zur Beschleunigung des Stoffübergangs und damit der Diffusion ausgenutzt. Mit Beginn der zweiten Periode wird das Kohlenstoffpotentialgefälle zur Vermeidung einer schädlichen Carbidbildung verringert und der Kohlenstoffpegel der Gasatmosphäre soweit abgesenkt, dass während der weiteren Diffusionsphase eine vorbestimmte Grenze des Kohlenstoffgehaltes der Randschicht nicht überschritten wird.A method based on this is disclosed in DE-A-31 39 622, the Enrichment phase through different regulation of the Carbon levels of the gas atmosphere in a first and a second period is divided. During the first period, the maximum possible Carbon potential gradient between the gas atmosphere and the boundary layer Acceleration of the mass transfer and thus the diffusion exploited. With The beginning of the second period is the carbon potential gradient to avoid harmful carbide formation and the carbon level of the Gas atmosphere lowered so far that during the further diffusion phase a predetermined limit of the carbon content of the surface layer is exceeded.
Überdies ist aus der EP-A-0 080 124 ein Verfahren zum Einsatzhärten metallischer Werkstücke bekannt, bei dem durch pulsierende Zugabe kohlenstoffhaltiger Gaskomponenten ein hohes Kohlenstoffpotentialgefälle erreicht wird. Die Zufuhr des kohlenstoffhaltigen Gases findet dabei in mehreren Zyklen statt und wird jeweils unterbrochen, sobald in der Randschicht eine Sättigung mit Kohlenstoff erreicht ist. Daneben offenbart die GB-A-2 202 238 ein Verfahren zum Aufkohlen von Werkstücken, bei dem sich die Anreicherungsphase und die Diffusionsphase bis zum Erreichen einer angestrebten Aufkohlungstiefe periodisch abwechseln, um den gewünschten Kohlenstoffgehalt der Randschicht und die angestrebte Aufkohlungstiefe weitgehend unabhängig voneinander und in möglichst kurzer Zeit zu erreichen.Furthermore, EP-A-0 080 124 describes a case hardening process known metallic workpieces, in which by pulsating addition carbon-containing gas components achieved a high carbon potential gradient becomes. The supply of the carbon-containing gas takes place in several cycles instead of and is interrupted as soon as saturation occurs in the boundary layer Carbon is reached. In addition, GB-A-2 202 238 discloses a method for Carburizing workpieces, in which the enrichment phase and the Diffusion phase periodically until a desired carburization depth is reached alternate to the desired carbon content of the surface layer and the target carburization depth largely independent of each other and in to achieve as short a time as possible.
Ein Verfahren sowie einer Vorrichtung zur thermischen oder thermomechanischen Behandlung von Stahl ist zudem aus der US 5,139,584 bekannt. Beschrieben wird mit dieser Patentschrift ein zweistufiges Behandlungsverfahren, das wie folgt durchgeführt wird: Eine erste Phase bei möglicher maximaler Temperatur, definiert ausgehend von metallurgischen Kriterien, mit Steuerung der Eintrittsmenge von Kohlenwasserstoffen zum Erhalt einer maximalen Konzentration von Kohlenstoffen an der Oberfläche, wobei diese maximale Konzentration wenigstens gleich der Sätttigungskonzentration von Kohlenstoff von Austenit ist; eine zweite Phase bei der möglichen maximalen Temperatur, definiert ausgehend von metallurgischen Kriterien, während der der Kohlenstoff-Fluß, der von der Gasphase übertragen wird, null ist, um das Kohlenstoffkonzentrationsprofil und insbesondere die Konzentration an der Oberfläche auf einen vorbestimmten Wert einzustellen, der nach metallurgischen Gründen gewählt ist. Vorgeschlagen wird dabei ein Wert von 0,7% bis 0,8% bei konventionellen Aufkohlungsstähle.A method and a device for thermal or thermomechanical Treatment of steel is also known from US 5,139,584. Is described with this patent, a two-step treatment process which is as follows is carried out: A first phase at possible maximum temperature, defined based on metallurgical criteria, with control of the entry quantity of Hydrocarbons to get a maximum concentration of carbons on the surface, this maximum concentration being at least equal to that Saturation concentration of carbon of austenite; a second phase at the possible maximum temperature, defined based on metallurgical Criteria during which the carbon flow is transferred from the gas phase is zero is the carbon concentration profile and in particular the Set the concentration on the surface to a predetermined value, the is chosen based on metallurgical reasons. A value of 0.7% to 0.8% for conventional carburizing steels.
Nachteilig bei all diesen Verfahren ist ein nicht immer befriedigendes Behandlungsergebnis. Dies ist vor allem darauf zurückzuführen, dass während einer sich an die Anreicherungsphase anschließenden Diffusionsphase oder Temperaturausgleichsphase keine unmittelbare Einflussnahme mehr auf den Kohlenstoffgehalt der Randschicht besteht. Dieser Umstand kommt in besonderem Maße dann zum Tragen, wenn sich geringe Anteile an Kohlendioxid oder Wasserdampf in der Gasatmosphäre befinden, die zum Beispiel aufgrund eines Lufteintritts an Leckstellen eines Wärmebehandlungsofens gebildet werden und die einen verstärkten Abbau des Kohlenstoffs in der Randschicht hervorrufen. Darüber hinaus enthalten die zur Regelung des Kohlenstoffpegels während der Anreicherungsphase eingesetzten Prozessgase erhebliche Anteile an sauerstoffhaltigen Komponenten, wie etwa Kohlenmonoxid, Kohlendioxid oder Wasserdampf, die aufgrund des Partialdruckes von Sauerstoff im äußeren Randbereich der aufgekohlten Randschicht eine unerwünschten Randoxidation verursachen. A disadvantage of all these methods is that they are not always satisfactory Treatment outcome. This is mainly due to the fact that during a diffusion phase following the enrichment phase or Temperature compensation phase no longer has any direct influence on the There is carbon content in the surface layer. This comes in particular Dimensions to be taken into account when there are small amounts of carbon dioxide or Water vapor are in the gas atmosphere, for example due to a Air entry at leaks of a heat treatment furnace are formed and the cause an increased degradation of the carbon in the surface layer. About that also contain those used to regulate carbon levels during the Process gases used in the enrichment phase oxygen-containing components, such as carbon monoxide, carbon dioxide or Water vapor due to the partial pressure of oxygen in the outside Edge area of the carburized edge layer an undesirable edge oxidation cause.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren und eine Vorrichtung zur Wärmebehandlung metallischer Werkstücke zu schaffen, mit denen sich bei Vermeidung einer Carbidbildung auf der Oberfläche der zu behandelnden Werkstücke auf vergleichsweise einfache Weise ein verbessertes Behandlungsergebnis erzielen lässt.The invention has for its object to provide a method and an apparatus for the heat treatment of metallic workpieces with which an improved treatment result can be achieved in a comparatively simple manner while avoiding carbide formation on the surface of the workpieces to be treated.
Diese Aufgabe wird erfindungsgemäß durch ein Verfahren zur Wärmebehandlung
metallischer Werkstücke, insbesondere zum Aufkohlen oder Carbonitrieren von
Eisenwerkstoffen, gelöst, das folgende Verfahrensschritte aufweist:
Ein solches Verfahren macht sich die Erkenntnis zu Eigen, dass sich ein verbessertes Behandlungsergebnis der Werkstücke dann erreichen lässt, wenn sowohl während der Anreicherungsphase als auch während der Diffusionsphase der Kohlenstoffgehalt der Randschicht durch Variieren der der Gasatmosphäre zugeführten Volumenströme an Stickstoff und Kohlenwasserstoff gezielt in einem vorgegebenen Intervall zwischen einer Untergrenze und einer Obergrenze eingestellt wird. Indem jeweils zunächst in einem ersten Abschnitt der Anteil an Stickstoff reduziert und der Anteil an Kohlenwasserstoff erhöht wird, ergibt sich ein hohes Kohlenstoffangebot in der Gasatmosphäre, das in verhältnismäßig kurzer Zeit den Kohlenstoffgehalt der Randschicht bis zu der vorgegebenen Obergrenze anreichert. Durch die nachfolgende Erhöhung des Anteils an Stickstoff und Reduzierung des Anteils an Kohlenwasserstoff in einem zweiten Abschnitt verringert sich das Kohlenstoffpotentialgefälle zwischen Gasatmosphäre und der Randschicht mit der Folge, dass der Kohlenstoffgehalt der Randschicht infolge der Diffusion des Kohlenstoffs in das Innere der Werkstücke auf die vorgegebene Untergrenze absinkt. Auf diese Weise lässt sich ein hinsichtlich der Oberfläche der zu behandelnden Werkstücke optimiertes Kohlenstoffangebot in der Gasatmosphäre bereitstellen, während es zugleich möglich ist, eine unerwünschte Carbid- oder Rußbildung auf der Oberfläche der Werkstücke zu vermeiden.Such a procedure adopts the knowledge that one can achieve improved treatment results of the workpieces if both during the enrichment phase and during the diffusion phase the carbon content of the boundary layer by varying that of the gas atmosphere supplied volume flows of nitrogen and hydrocarbon in one predetermined interval between a lower limit and an upper limit is set. By first in each case in a first section Nitrogen is reduced and the proportion of hydrocarbon is increased high carbon supply in the gas atmosphere, which in a relatively short Time the carbon content of the boundary layer up to the specified upper limit accumulates. By subsequently increasing the proportion of nitrogen and Reduction of the hydrocarbon content in a second section the carbon potential difference between the gas atmosphere and the Surface layer with the consequence that the carbon content of the surface layer as a result of Diffusion of the carbon into the interior of the workpieces to the given Lower limit drops. In this way, the surface of the Workpieces to be treated optimized carbon supply in the Provide gas atmosphere while it is also possible to create an undesirable one Avoid carbide or soot formation on the surface of the workpieces.
Die Temperatur, auf die in der Aufheizphase erwärmt wird, die Zeitdauer, für welche die Werkstücke auf dieser Temperatur während der Ausgleichsphase gehalten werden, die Temperaturen, die in der Anreicherungsphase und der Diffusionsphase eingestellt werden, und die in den jeweiligen Verfahrensstadien zugeführten Mengen an Stickstoff und Kohlenstoff richten sich vor allem nach dem Werkstoff der zu behandelnden Werkstücke, der zum Erreichen des angestrebten Kohlenstoffgehalts der Randschicht erforderlichen spezifischen Zusammensetzung der Gasatmosphäre und dem angestrebten Behandlungserfolg, etwa der gewünschten Aufkohlungstiefe. Da die Prozessparameter von den Werkstoffeigenschaften der zu behandelnden Werkstücke abhängen, lassen sich aus allgemein zugänglichen Datenbanken, wie etwa der Calphad (Calculation of phase diagrams), Stockholm, die für eine bestimmte Stahlzusammensetzung notwendigen Parameterwerte in Hinsicht auf den angestrebten Kohlenstoffgehalt in der Randschicht entnehmen.The temperature to which heating takes place in the heating phase, the length of time for which the workpieces are kept at this temperature during the compensation phase, the temperatures which are set in the enrichment phase and the diffusion phase, and the amounts of nitrogen supplied in the respective process stages and carbon depend primarily on the material of the workpieces to be treated, the specific composition of the gas atmosphere required to achieve the desired carbon content of the surface layer and the desired treatment success, such as the desired carburization depth. Since the process parameters of the material properties depend on the workpieces to be treated, can be obtained from publicly available databases, such as the Calphad (Cal culation of pha se d iagrams), Stockholm, necessary for a particular steel composition parameter values with respect to the desired carbon content in the Remove surface layer.
Besonders vorteilhaft ist es, durch eine abwechselnde Wiederholung der ersten und zweiten Abschnitte während der Anreicherungsphase und/oder der Diffusionsphase die Anreicherung der Randschicht mit Kohlenstoff entsprechend dem von dem jeweiligen Werkstoff abhängenden Aufnahmevermögen der Werkstücke anzupassen. In Hinsicht auf die beim Carbonitrieren erforderliche Freisetzung von diffusionsfähigem Stickstoff kann es zudem von Vorteil sein, während der Anreicherungsphase und/oder der Diffusionsphase der Gasatmosphäre Ammoniak, vorzugsweise in einer Größenordnung von 2 Vol.-% bis 20 Vol.-% der Gesamtbegasungsrate, zuzusetzen. Als vorteilhaft hat sich ferner herausgestellt, die Mengen an Stickstoff und Kohlenwasserstoff in der Gasatmosphäre während der Anreicherungsphase und der Diffusionsphase derart zu variieren, dass die Untergrenze des Kohlenstoffgehalts der Randschicht zwischen 0,5 Gew.-% und 0,8 Gew.-% liegt. Bei solch einem Kohlenstoffgehalt der Randschicht ist der Anteil an Stickstoff in der Gasatmosphäre noch ausreichend hoch, um eine sichere Wärmebehandlung zu gewährleisten. It is particularly advantageous to repeat the first one alternately and second sections during the enrichment phase and / or the Diffusion phase corresponding to the enrichment of the surface layer with carbon the absorption capacity of the depending on the respective material To adapt workpieces. With regard to that required for carbonitriding Release of diffusible nitrogen can also be advantageous during the enrichment phase and / or the diffusion phase of the Ammonia gas atmosphere, preferably in the order of 2% by volume up to 20 vol% of the total gassing rate. Has proven to be beneficial also highlighted the amounts of nitrogen and hydrocarbon in the Such gas atmosphere during the enrichment phase and the diffusion phase to vary that the lower limit of the carbon content of the surface layer is between 0.5% and 0.8% by weight. With such a carbon content the Boundary layer, the proportion of nitrogen in the gas atmosphere is still sufficient high to ensure safe heat treatment.
Um eine unerwünschte Carbid- oder Rußbildung auf der Oberfläche der Werkstücke definitiv auszuschließen, werden die Mengen an Stickstoff und Kohlenwasserstoff in der Gasatmosphäre während der Anreicherungsphase und/oder der Diffusionsphase vorteilhafterweise derart variiert, dass die Obergrenze des Kohlenstoffgehalts der Randschicht geringfügig unterhalb der durch eine bei der jeweils herrschenden Temperatur auftretenden Carbidbildung gekennzeichneten Sättigung von Austenit liegt. Die Obergrenze des Kohlenstoffgehalts der Randschicht kann dabei während der Diffusionsphase so gewählt werden, dass sie den Erfordernissen eines in der nachfolgenden Abkühlungsphase stattfindenden Härteprozesses entspricht.To prevent undesirable carbide or soot formation on the surface of the Definitely exclude workpieces, the amounts of nitrogen and Hydrocarbon in the gas atmosphere during the enrichment phase and / or the diffusion phase advantageously varies such that the Upper limit of the carbon content of the surface layer slightly below the due to carbide formation occurring at the prevailing temperature marked saturation of austenite. The upper limit of Carbon content of the surface layer can be so during the diffusion phase be chosen to meet the requirements of one of the following Cooling phase taking place corresponds to the hardening process.
Eine besonders vorteilhafte Verfahrensführung ist außerdem dann gegeben, wenn die Werkstücke während der Aufheizphase auf eine für ein Aufkohlen oder Carbonitrieren günstige Temperatur zwischen 750°C und 1050°C erwärmt werden. Von besonderem Vorteil ist zudem ein Kohlenstoffgehalt der Randschicht während der Aufheizphase im Bereich zwischen 0,2 Gew.-% und 0,5 Gew.-%. Möglicherweise auf den Werkstücken vorhandene Oxid- oder Passivschichten werden auf diese Weise beseitigt oder zumindest so umgewandelt, dass eine gleichmäßige Diffusion des Kohlenstoffs in den Werkstoff begünstigt wird. Zu diesem Zweck ist es überdies nützlich, die Werkstücke während der Ausgleichsphase für eine Zeitdauer von 0,1 h bis 1 h auf der am Ende der Aufheizphase erreichten Temperatur zu halten. Im Hinblick auf eine dem angestrebten Behandlungserfolg entsprechende Verfahrensführung kann außerdem eine bezüglich der Anreicherungsphase reduzierte Temperatur während der Diffusionsphase zweckdienlich sein.A particularly advantageous procedure is also given if the workpieces during the heating phase to one for carburizing or Carbonitriding favorable temperature between 750 ° C and 1050 ° C to be heated. A carbon content of the surface layer is also of particular advantage during the heating phase in the range between 0.2 wt .-% and 0.5 wt .-%. Possibly existing oxide or passive layers on the workpieces are eliminated in this way or at least converted so that a uniform diffusion of carbon into the material is favored. To for this purpose it is also useful to remove the workpieces during the Compensation phase for a period of 0.1 h to 1 h at the end of the Keep heating temperature reached. With regard to one desired treatment success corresponding procedure management also a reduced temperature during the enrichment phase during the diffusion phase be useful.
Eine besonders vorteilhafte Verfahrensführung ist ferner dann gegeben, wenn ungesättigte Kohlenwasserstoffe des Typs CnH2n, vorzugsweise Alkene wie etwa Ethylen (C2H4) und Propylen (C3H6), gesättigte Kohlenwasserstoffe des Typs CnH2n+2, vorzugsweise Alkane wie etwa Ethan (C2H6) und Propan (C3H8), oder Alkine wie etwa Acetylen (C2H2) der Gasatmosphäre beigegeben werden. Vornehmlich Alkine, die sich durch einen geringen Anteil an Wasserstoff auszeichnen, bieten den Vorteil, dass keine weiteren Spaltprodukte erzeugt werden und der Anteil an Wasserstoff in der Gasatmosphäre dementsprechend gering bleibt. Um bei gegebenenfalls in der Gasatmosphäre vorhandenem Sauerstoff, der beispielsweise von einem Lufteintritt an Leckstellen eines Wärmebehandlungsofens herrührt, einen reduzierenden und damit eine Oxidation der zu behandelnden Werkstücke vermeidenden Zustand der Gasatmosphäre zu erhalten, wird in vorteilhafter Weise ein Reduktionsmittel, vorzugsweise Wasserstoff, der Gasatmosphäre in konstanter oder variabler Menge beigegeben. Der Zeitpunkt und die Menge der Zufuhr an Reduktionsmittel richten sich dabei nach den jeweils vorhandenen Umständen.A particularly advantageous procedure is also given when unsaturated hydrocarbons of the type C n H 2n , preferably alkenes such as ethylene (C 2 H 4 ) and propylene (C 3 H 6 ), saturated hydrocarbons of the type C n H 2n + 2 , preferably alkanes such as ethane (C 2 H 6 ) and propane (C 3 H 8 ), or alkynes such as acetylene (C 2 H 2 ) are added to the gas atmosphere. Primarily alkynes, which are characterized by a low proportion of hydrogen, offer the advantage that no further fission products are generated and the proportion of hydrogen in the gas atmosphere accordingly remains low. In order to obtain a reducing and thus avoiding oxidation of the workpieces to be treated, a reducing agent, preferably hydrogen, is advantageously added to the gas atmosphere in the case of oxygen present in the gas atmosphere, which stems, for example, from an air inlet at leaks in a heat treatment furnace constant or variable amount added. The point in time and the amount of reducing agent added depend on the prevailing circumstances.
In einer besonders vorteilhaften Weiterbildung des erfindungsgemäßen Verfahrens, wird die Zufuhr der Mengen an Stickstoff und Kohlenwasserstoff in die Gasatmosphäre in Abhängigkeit von einem den Kohlenstoffgehalt in der Randschicht repräsentierenden Kennwert, vorzugsweise der Kohlungskennzahl Kc, geregelt oder datenbankbezogen gesteuert. Die datenbankbezogene Steuerung ist dann von Vorteil, wenn ein den Kohlenstoffgehalt in der Randschicht repräsentierender Kennwert etwa aufgrund messtechnischer Schwierigkeiten nicht zur Verfügung steht. Die Regelung der Zufuhr in Abhängigkeit von einem den Kohlenstoffgehalt in der Randschicht repräsentierenden Kennwert hingegen ermöglicht eine genaue Einstellung des angestrebten Kohlenstoffgehalts der Randschicht, und zwar ohne dass es in besonderem Maße auf die jeweilige Größe der Oberfläche der zu behandelnden Werkstücke ankommt. Die über den Kohlenstoffgehalt in der Randschicht Aufschluss gebende Kohlungskennzahl Kc wird beispielsweise durch den Quotienten des Partialdrucks von Methan (pCH4) und des Quadrats des Partialdrucks von Wasserstoff (pH2 2) errechnet (Kc = pCH4 / pH2 2).In a particularly advantageous development of the method according to the invention, the supply of the amounts of nitrogen and hydrocarbon into the gas atmosphere is regulated or controlled in a database-dependent manner as a function of a characteristic value representing the carbon content in the surface layer, preferably the carbonation index K c . The database-related control is advantageous if a characteristic value representing the carbon content in the surface layer is not available, for example due to measurement difficulties. The regulation of the supply as a function of a characteristic value representing the carbon content in the surface layer, on the other hand, enables the desired carbon content of the surface layer to be set precisely, without the size of the surface of the workpieces to be treated being particularly important. The carbon index K c , which gives information about the carbon content in the surface layer, is calculated, for example, by the quotient of the partial pressure of methane (p CH4 ) and the square of the partial pressure of hydrogen (p H2 2 ) (K c = p CH4 / p H2 2 ).
Zweckmäßigerweise werden die Werkstücke während der Abkühlungsphase in einer reduzierenden oder neutralen Gasatmosphäre oder in einem flüssigen Abschreckmedium auf Raumtemperatur abgekühlt.The workpieces are expediently removed during the cooling phase a reducing or neutral gas atmosphere or in a liquid Quench medium cooled to room temperature.
Zur Lösung der obigen Aufgabe wird außerdem eine Vorrichtung zur Wärmebehandlung metallischetwerkstücke vorgeschlagen, die eine Heizkammer, in der die Werkstücke erwärmbar und einer Stickstoff und einen Kohlenwasserstoff enthaltenden Gasatmosphäre aussetzbar sind, aufweist und sich dadurch auszeichnet, dass Mittel vorgesehen sind, mit denen die Zufuhr der Mengen an Stickstoff und Kohlenwasserstoff in die Gasatmosphäre in Abhängigkeit von einem den Kohlenstoffgehalt in der Randschicht repräsentierenden Kennwert, vorzugsweise der Kohlungskennzahl Kc, regelbar oder datenbankbezogen steuerbar ist, wobei als Mittel zur Messung des den Kohlenstoffgehalt in der Randschicht repräsentierenden Kennwertes ein innerhalb der Heizkammer angeordneter Drahtsensor vorgesehen ist, und daß Mittel vorgesehen sind, mit denen die Zufuhr der Menge eines Reduktionsmittels, vorzugsweise Wasserstoff, und/oder Ammoniak regelbar oder datenbankbezogen steuerbar ist. Mit solch einer Vorrichtung lässt sich das erfindungsgemäße Verfahren in zuverlässiger Weise durchführen.To solve the above object, a device for heat treatment of metallic workpieces is also proposed, which has a heating chamber in which the workpieces can be heated and exposed to a gas atmosphere containing nitrogen and a hydrocarbon, and is characterized in that means are provided with which the supply of the Amounts of nitrogen and hydrocarbon in the gas atmosphere as a function of a characteristic value representing the carbon content in the boundary layer, preferably the carbon index K c , can be regulated or controlled in a database-related manner, with a means arranged within the heating chamber as a means of measuring the characteristic value representing the carbon content in the boundary layer Wire sensor is provided, and that means are provided with which the supply of the amount of a reducing agent, preferably hydrogen, and / or ammonia can be regulated or controlled in a database-related manner. The method according to the invention can be carried out in a reliable manner with such a device.
In Weiterbildung dieser Vorrichtung wird ferner vorgeschlagen, dass die Heizkammer hermetisch abschließbar ausgebildet ist, um das Eindringen von Luft und damit Sauerstoff in die Gasatmosphäre zu vermeiden. Schließlich wird vorgeschlagen, dass die Heizkammer mit einem Inertgas, vorzugsweise Stickstoff, spülbar ist, so dass unabhängig vom Volumen der Heizkammer der Gehalt an Sauerstoff in der Atmosphäre der Heizkammer nach Einbringen der zu behandelnden Werkstücke in vergleichsweise kurzer Zeit auf < 1 Vol.-% reduzierbar und eine unerwünschte Oxidation der zu behandelnden Werkstücke hierdurch vermeidbar ist.In a further development of this device, it is also proposed that the Heating chamber is hermetically sealed to prevent air from entering and thus avoid oxygen in the gas atmosphere. Eventually proposed that the heating chamber be filled with an inert gas, preferably nitrogen, is flushable, so that regardless of the volume of the heating chamber the content of Oxygen in the atmosphere of the heating chamber after introduction of the treating workpieces in a comparatively short time to <1% by volume reducible and undesirable oxidation of the workpieces to be treated this is avoidable.
Einzelheiten und weitere Vorteile der Gegenstände der vorliegenden Erfindung
ergeben sich aus der nachfolgenden Beschreibung eines bevorzugten
Ausführungsbeispieles. In der zugehörigen Zeichnung zeigt die einzige Figur:
Bei dem in Fig. 1 dargestellten Diagramm sind auf der Abszisse die Zeit t und auf
der Ordinate die Temperatur ϑ, der sich in der Randschicht zu behandelnder
Werkstücke ergebende Kohlenstoffgehalt wc, und die einer Gasatmosphäre zu
diesem Zweck zugeführten Volumenströme an Wasserstoff V ˙ H
Während einer auf die Aufheizphase A folgenden Ausgleichsphase B werden die
Werkstücke auf der am Ende der Aufheizphase A erreichten Temperatur ϑ von
ca. 930 °C für ca. 20 min gehalten. Die dabei in die Gasatmosphäre zugeführten
Mengen an Stickstoff V ˙ N
In einer sich an die Ausgleichsphase B anschießenden Anreicherungsphase C
werden die der Gasatmosphäre zugeführten Volumenströme an Stickstoff V ˙ N
Auf die Anreicherungsphase C folgt eine Diffusionsphase D, bei der die
Temperatur ϑ auf ca. 880°C verringert wird. In Hinsicht auf einen nachfolgenden
Härteprozess wird die Obergrenze Go auf ca. 0,8 Gew.-% herabgesetzt.
Entsprechend der Vorgehensweise während der Anreicherungsphase C wird das
thermodynamische Gleichgewicht zwischen der Gasatmosphäre und der
Randschicht der zu behandelnden Werkstücke durch Variieren der der
Gasatmosphäre zugeführten Volumenströme an Stickstoff V ˙ N
Findet anstelle eines reinen Aufkohlungsprozesses ein Carbonitrieren statt, kann -
wie in Fig. 1 ersichtlich - der Gasatmosphäre während der Anreicherungsphase C
und der Diffusionsphase D zusätzlich Ammoniak V ˙ NH
Das zuvor beschriebene Verfahren zeichnet sich durch die volumenstrommäßige
Regelung der der Gasatmosphäre zugeführten Mengen an Stickstoff V ˙ N
- AA
- Aufheizphaseheating phase
- BB
- Ausgleichsphasebalancing phase
- CC
- Anreicherungsphaseenrichment phase
- DD
- Diffusionsphasediffusion phase
- Ee
- Abkühlungsphasecooling phase
- tt
- Zeittime
- ϑθ
- Temperaturtemperature
- wc w c
- KohlenstoffgehaltCarbon content
- Go G o
- Obergrenze KohlenstoffgehaltUpper carbon limit
- Gu G u
- Untergrenze KohlenstoffgehaltLower limit carbon content
-
V ˙V ˙
CC
22 HH22 - Volumenstrom AcetylenVolume flow acetylene
-
V ˙V ˙
NN
22 - Volumenstrom StickstoffVolume flow nitrogen
-
V ˙V ˙
HH
22 - Volumenstrom WasserstoffVolume flow hydrogen
-
V ˙V ˙
NHNH
33 - Volumenstrom AmmoniakVolume flow ammonia
Claims (16)
- Method of heat treatment of metal workpieces, particularly for carburising or carbonitriding iron workpieces, comprising the following method steps:a) heating of the workpieces to a specific temperature (ϑ) in a gaseous atmosphere containing nitrogen and a hydrocarbon during a heating phase (A), wherein the supply of quantities of nitrogen (V ˙ C
2 H2 ) and hydrocarbon (V ˙ C2 H2 ) into the gaseous atmosphere is regulated in such a way that an edge layer forms on the workpieces with a carbon content (wc) within a predetermined range;b) keeping the workpieces at the temperature (ϑ) reached at the end of the heating phase (A) for a specific period of time during a subsequent balancing phase (B), wherein the carbon content (wc) of the edge layer still lies within the predetermined range due to the quantities of nitrogen (V ˙ N2 ) and hydrocarbon (V ˙ C2 H2 ) supplied with the gaseous atmosphere;c) varying the quantities of nitrogen (V ˙ N2 ) and hydrocarbon (V ˙ C2 H2 ) in the gaseous atmosphere during an enrichment phase (C) which follows the balancing phase (B) and during a subsequent diffusion phase (D), wherein in each case first of all in a first period in order to reach a predetermined upper limit (Go) of the carbon content (wc) of the edge layer the proportion of nitrogen ( V ˙ N2 ) is reduced and the proportion of hydrocarbon (V ˙ C2 H2 ) is increased and then in a second period in order to reach a predetermined lower limit (Gu) of the carbon content (wc) of the edge layer the proportion of nitrogen (V ˙ N2 ) is increased and the proportion of hydrocarbon (V ˙ C2 H2 ) is reduced;d) cooling of the workpieces to room temperature during a cooling phase (E) following the diffusion phase (D). - Method as claimed in Claim 1, characterised by an alternating repetition of the first and second periods during the enrichment phase (C) and/or the diffusion phase (D).
- Method as claimed in either Claim 1 or Claim 2, characterised in that during the enrichment phase (C) and/or the diffusion phase (D) ammonia (V ˙ NH
3 ) is added to the gaseous atmosphere, preferably in the order of magnitude of 2% to 20% by volume of the total quantity of gas injected. - Method as claimed in any one of Claims 1 to 3, characterised in that the quantities of nitrogen (V ˙ N
2 ) and hydrocarbon (V ˙ C2 H2 ) in the gaseous atmosphere are varied during the enrichment phase (C) and the diffusion phase (D) in such a way that the lower limit (Gu) of the carbon content (wc) of the edge layer is between 0.5% and 0.8% by weight. - Method as claimed in any one of Claims 1 to 4, characterised in that the quantities of nitrogen (V ˙ N
2 ) and hydrocarbon (V ˙ C2 H2 ) in the gaseous atmosphere are varied during the enrichment phase (C) in such a way that the upper limit (Go) of the carbon content (wc) of the edge layer is slightly below the austenite saturation characterised by a carbide formation at the respective prevailing temperature (ϑ). - Method as claimed in any one of Claims 1 to 5, characterised in that the workpieces are heated during the heating phase (A) to a temperature (ϑ) between 750°C and 1050°C.
- Method as claimed in any one of Claims 1 to 6, characterised by a carbon content (wc) of the edge layer during the heating phase (A) in the range between 0.2% by weight and 0.5% by weight.
- Method as claimed in any one of Claims 1 to 7, characterised in that during the balancing phase (B) the workpieces are kept for a period of 0.1 h to 1 h at the temperature (ϑ) reached at the end of the heating phase (A).
- Method as claimed in any one of Claims 1 to 8, characterised by a temperature (ϑ) during the diffusion phase (D) which is reduced relative to the enrichment phase (C).
- Method as claimed in any one of Claims 1 to 9, characterised in that unsaturated hydrocarbons of the CnH2n type, preferably alkenes such as for instance ethylene (C2H4) and propylene (C3H6), saturated hydrocarbons of the CnH2n+2 type, preferably alkanes such as for instance ethane (C2H6) and propane (C3H8), or alkynes such as for instance acetylene (C2H2) are added to the gaseous atmosphere.
- Method as claimed in any one of Claims 1 to 10, characterised in that a reducing agent, preferably hydrogen ( .V H
2 ), is added to the gaseous atmosphere in a constant or variable quantity. - Method as claimed in any one of Claims 1 to 11, characterised in that the supply of quantities of nitrogen (V ˙ N
2 ) and hydrocarbon (V ˙ C2 H2 ) to the gaseous atmosphere is regulated as a function of a characteristic value representing the carbon content (wc) in the edge layer, preferably the carbonisation characteristic quantity Kc, or is controlled in relation to a database. - Method as claimed in any one of Claims 1 to 12, characterised in that the during the cooling phase (E) the workpieces are cooled to room temperature in a reducing or neutral gaseous atmosphere or in a liquid quenching medium.
- Apparatus for the heat treatment of metal workpieces, particularly for carrying out the method as claimed in any one of Claims 1 to 13, with a heating chamber in which the workpieces can be heated and can be exposed to a gaseous atmosphere containing nitrogen and a hydrocarbon, characterised in that means are provided by which the supply of quantities of nitrogen (V ˙ N
2 ) and hydrocarbon (V ˙ C2 H2 ) to the gaseous atmosphere is regulated as a function of a characteristic value representing the carbon content (wc) in the edge layer, preferably the carbonisation characteristic quantity Kc, or is controlled in relation to a database, wherein a wire sensor disposed inside the heating chamber is provided as means for measuring the characteristic value representing the carbon content in the edge layer, and that means are provided by which the supply of the quantity of a reducing agent, preferably hydrogen (V ˙ H2 ), and/or ammonia (V ˙ NH3 ) can be regulated or can be controlled in relation to a database. - Apparatus as claimed in Claim 14, characterised in that the heating chamber is constructed so that it can be hermetically sealed.
- Apparatus as claimed in either one of Claims 14 or 15, characterised in that the heating chamber can be flushed with an inert gas, preferably nitrogen.
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DE50007480T DE50007480D1 (en) | 2000-05-24 | 2000-05-24 | Method and device for the heat treatment of metallic workpieces |
AT00111129T ATE274073T1 (en) | 2000-05-24 | 2000-05-24 | METHOD AND DEVICE FOR THE HEAT TREATMENT OF METAL WORKPIECES |
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US7550049B2 (en) | 2002-10-31 | 2009-06-23 | Seco/Warwick S.A. | Method for under-pressure carburizing of steel workpieces |
DE102010028165A1 (en) * | 2010-04-23 | 2011-10-27 | Robert Bosch Gmbh | Process for the carbonitriding of metallic components |
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DE10221605A1 (en) * | 2002-05-15 | 2003-12-04 | Linde Ag | Method and device for the heat treatment of metallic workpieces |
WO2005038076A1 (en) * | 2003-10-14 | 2005-04-28 | Etudes Et Constructions Mecaniques | Low-pressure carburising method and furnace |
FR2884523B1 (en) | 2005-04-19 | 2008-01-11 | Const Mecaniques Sa Et | LOW PRESSURE CARBONITRUTING PROCESS AND FURNACE |
US20080149226A1 (en) * | 2006-12-26 | 2008-06-26 | Karen Anne Connery | Method of optimizing an oxygen free heat treating process |
DE112010005929A5 (en) | 2010-10-11 | 2014-01-02 | Ipsen International Gmbh | Method and device for carburizing and carbonitriding metallic materials |
DE102014113846A1 (en) * | 2014-09-24 | 2016-03-24 | Härterei Technotherm Gmbh & Co. Kg | Process for treating a ferrous material and treated ferrous material |
Family Cites Families (4)
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---|---|---|---|---|
DE3146042A1 (en) * | 1981-11-20 | 1983-05-26 | Linde Ag, 6200 Wiesbaden | METHOD FOR USEFUL METAL WORKPIECES |
US5139584A (en) * | 1989-07-13 | 1992-08-18 | Solo Fours Industriels Sa | Carburization process |
DE19704871C1 (en) * | 1997-02-10 | 1998-10-15 | Will Haertetechnik Gmbh | Hardening hollow cold extruded steel shaft |
FR2777911B1 (en) * | 1998-04-28 | 2000-07-28 | Aubert & Duval Sa | LOW PRESSURE CARBONITRURATION OF METAL ALLOY PARTS |
-
2000
- 2000-05-24 DE DE50007480T patent/DE50007480D1/en not_active Expired - Lifetime
- 2000-05-24 AT AT00111129T patent/ATE274073T1/en not_active IP Right Cessation
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US7550049B2 (en) | 2002-10-31 | 2009-06-23 | Seco/Warwick S.A. | Method for under-pressure carburizing of steel workpieces |
DE102010028165A1 (en) * | 2010-04-23 | 2011-10-27 | Robert Bosch Gmbh | Process for the carbonitriding of metallic components |
Also Published As
Publication number | Publication date |
---|---|
EP1160349A1 (en) | 2001-12-05 |
DE50007480D1 (en) | 2004-09-23 |
ATE274073T1 (en) | 2004-09-15 |
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