EP0545069B1 - Method of treating steel and refractory metals - Google Patents

Method of treating steel and refractory metals Download PDF

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Publication number
EP0545069B1
EP0545069B1 EP92118403A EP92118403A EP0545069B1 EP 0545069 B1 EP0545069 B1 EP 0545069B1 EP 92118403 A EP92118403 A EP 92118403A EP 92118403 A EP92118403 A EP 92118403A EP 0545069 B1 EP0545069 B1 EP 0545069B1
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Prior art keywords
temperature
oxidation
pressure
thermochemical
steels
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EP92118403A
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German (de)
French (fr)
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EP0545069A1 (en
Inventor
Albrecht Dr. Melber
Peter Dr. Minarski
Friedrich Dr. Preisser
Klaus Dr. Zimmermann
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Leybold Durferrit GmbH
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Leybold Durferrit GmbH
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Priority claimed from DE4139975A external-priority patent/DE4139975C2/en
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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
    • C23C8/02—Pretreatment of the material to be coated
    • 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
    • C23C8/80—After-treatment

Definitions

  • the invention relates to a method for treating components made of steels and metals in a process chamber under the action of pressure and temperature with a first process step in which a thermochemical surface treatment, for example case hardening, is carried out, for which purpose a gas or gas mixture is let into this process chamber .
  • a thermochemical surface treatment for example case hardening
  • thermochemical surface treatment e.g. nitriding, nitro-carburizing or boriding
  • refractory metals e.g. Ti, Zr, Mo, W. Nb, Ta, V
  • Passive layers on the materials lead to the following difficulties:
  • the passive layers mostly consist of oxides and form a thin protective skin, which disadvantageously prevents the undisturbed diffusion of non-metals such as N, C, and B during surface treatment. This completely prevents diffusion, for example in the case of refractory metals, and in some cases in the case of high-alloy steels, which leads to uneven treatment results.
  • pre-oxidation is carried out in order to achieve a uniform treatment result. This means that contaminations on the surfaces are oxidized and the already existing oxide layer is influenced. In some cases, this can influence the uniformity of the layer formation.
  • the layers produced are very thin and contain ever larger amounts of oxygen.
  • thermochemical surface treatment of metals e.g. carburizing, tempering, annealing, carbonitriding, nitrocarburizing
  • edge oxidation This edge oxidation reduces the fatigue strength, so that the life of edge-oxidized components is reduced.
  • the object of the present invention is now to develop a method which removes the edge oxidation of heat-treated parts and replaces the mechanical processing.
  • thermochemical removal of the edge oxidation generated as a result of the first process step on the components in a second process step N2 H2 or NH3 or a mixture of these gases in the process chamber and a pressure greater than 1 bar and a temperature between 100 ° C and 1,000 ° C are set independently.
  • the oxides are reduced by reacting with the gas phase and releasing their oxygen atoms or forming nitrides.
  • parts heat-treated in this way can be almost completely deoxidized.
  • Such a heat treatment can be carried out for higher-alloy steels as a replacement for the tempering treatment which is to be carried out anyway, tempering and deoxidizing are then carried out in one step.
  • thermochemical treatments with oxidizing gas components and to achieve higher fatigue strength properties on the components through the subsequent deoxidation.
  • the use of expensive and complicated mechanical post-treatments can be dispensed with.
  • the invention allows for a wide variety of designs; one of them is shown as an example in the two attached sketches.
  • the steel After the steel has been introduced into a treatment chamber 1, it is heated to 580 ° C and at a pressure of e.g. 10 bar H2 and / or NH3 is let in. In this process step, the steel used is de-passivated and at the same time provided with a thin nitride layer as protection against further oxidation.
  • the steel which is protected against oxidation, is then brought into a second treatment chamber 2.
  • a material-specific nitriding temperature of 550 ° C is set and a gas mixture of NH3, H2 is let in at a pressure of 1 bar.
  • a nitrided X 20 CrMo V 12 1 steel is obtained as the end product.
  • carbon-containing gases such as CO2 or CO can be used for coal at temperatures between 800 ° C and 1,000 ° C.
  • thermochemical treatment process for example nitriding can be carried out in a conventional nitriding plant under atmospheric pressure. This eliminates the need to use a pressure chamber, which must be designed for 30 bar, for example.

Abstract

Method for treating steels and metals, especially for depassivating and subsequent thermochemical surface treatment in a process chamber (1,2) under the influence of pressure and temperature, wherein, in a first process step, a first gas or gas mixture selected from the group N2, H2 or NH3 is introduced in a process chamber (1) for the purpose of depassivation, a pressure greater than 1 bar absolute and a temperature between 100 DEG C and 1,000 DEG C being settable in the chamber (1), and in a second process step a second gas or gas mixture selected from the group of N-, C- or B-containing gases is introduced into a process chamber (1,2) for the purpose of thermochemical surface treatment, and a temperature between 100 DEG C and 1,000 DEG C at a pressure greater than or equal to 1 bar absolute being settable. <IMAGE>

Description

Die Erfindung betrifft ein Verfahren zur Behandlung von Bauteilen aus Stählen und Metallen in einer Prozeßkammer unter Einwirkung von Druck und Temperatur mit einem ersten Verfahrensschritt, in dem eine thermochemische Oberflächenbehandlung, beispielsweise das Einsatzhärten, durchgeführt wird, wozu ein Gas oder Gasgemisch in diese Prozeßkammer eingelassen wird.The invention relates to a method for treating components made of steels and metals in a process chamber under the action of pressure and temperature with a first process step in which a thermochemical surface treatment, for example case hardening, is carried out, for which purpose a gas or gas mixture is let into this process chamber .

Bei der thermochemischen Oberflächenbehandlung (z.B. Nitrieren, Nitrokarburieren oder Borieren) von legierten Stählen und Refraktärmetallen (z.B. Ti, Zr, Mo, W. Nb, Ta, V) kommt es bislang durch die oberflächenbedeckenden Passivschichten auf den Materialien zu folgenden Schwierigkeiten: Die Passivschichten bestehen nämlich meist aus Oxiden und bilden eine dünne Schutzhaut, die das ungestörte Eindiffundieren von Nichtmetallen wie z.B. N, C, und B bei der Oberflächenbehandlung mit Nachteil verhindern. Dadurch wird z.B. bei den Refraktärmetallen eine Eindiffusion völlig, bei hochlegierten Stählen teilweise verhindert, was zu ungleichmäßigen Behandlungsergebnissen führt.
Bei bestimmten Sorten legierter Stähle wird zu Erzielung eines gleichmäßigen Behandlungsergebnisses eine Voroxidation vorgenommen. Damit werden Verunreinigungen an den Oberflächen oxidiert und die bereits bestehende Oxidschicht beeinflußt. Dadurch kann in manchen Fällen Einfluß auf die Gleichmäßigkeit der Schichtausbildung genommen werden. Die erzeugten Schichten sind sehr dünn und enthalten immer größere Mengen Sauerstoff.In the thermochemical surface treatment (e.g. nitriding, nitro-carburizing or boriding) of alloyed steels and refractory metals (e.g. Ti, Zr, Mo, W. Nb, Ta, V), the surface covering has so far been used Passive layers on the materials lead to the following difficulties: The passive layers mostly consist of oxides and form a thin protective skin, which disadvantageously prevents the undisturbed diffusion of non-metals such as N, C, and B during surface treatment. This completely prevents diffusion, for example in the case of refractory metals, and in some cases in the case of high-alloy steels, which leads to uneven treatment results.
For certain types of alloyed steel, pre-oxidation is carried out in order to achieve a uniform treatment result. This means that contaminations on the surfaces are oxidized and the already existing oxide layer is influenced. In some cases, this can influence the uniformity of the layer formation. The layers produced are very thin and contain ever larger amounts of oxygen.

Bei der thermochemischen Oberflächenbehandlung von Metallen (z.B. Aufkohlen, Vergüten, Glühen, Carbonitrieren, Nitrocarburieren) kommt es weiterhin, bedingt durch die Verwendung sauerstoffhaltiger Prozeßgase zu einer interkristallinen Oxidation der behandelten Bauteile. Da die Oxidation nur an der freien Oberfläche, also am Rand der Bauteile auftritt, wird diese Form der Oxidation auch als Randoxidation bezeichnet. Diese Randoxidation bewirkt eine Herabsetzung der Dauerfestigkeit, so daß die Lebensdauer randoxidierter Bauteile verkleinert wird.In the thermochemical surface treatment of metals (e.g. carburizing, tempering, annealing, carbonitriding, nitrocarburizing), there is still an intercrystalline oxidation of the treated components due to the use of oxygen-containing process gases. Since the oxidation only occurs on the free surface, i.e. on the edge of the components, this form of oxidation is also referred to as edge oxidation. This edge oxidation reduces the fatigue strength, so that the life of edge-oxidized components is reduced.

Es sind zur Zeit zwei Wärmebehandlungsverfahren zum Aufkohlen von Werkstücken bekannt, die mit sauerstofffreien Prozeßgasen betrieben werden. Diese Verfahren, Plasmaaufkohlung und Vakuumaufkohlung, konnten bisher jedoch noch keine industrielle Anwendung in nennenswertem Umfang finden.
Bauteile, die nach der Wärmebehandlung Oxidation aufweisen, werden daher meist durch mechanische Bearbeitung nachbehandelt, mit dem Ziel die Oxidation abzutragen (z.B. Schleifen von Zahnrädern). Der Abfall der Dauerfestigkeit durch Randoxidation kann auch durch Verfahren zur Verfestigung (z.B. Kugelstrahlen von Zahnrädern) der Bauteile kompensiert werden.There are currently two heat treatment processes for carburizing workpieces that are operated with oxygen-free process gases. These processes, plasma carburizing and vacuum carburizing, have so far been able to find no significant industrial application.
Components that have oxidation after heat treatment are therefore usually post-treated with mechanical processing with the aim of removing the oxidation (eg grinding gear wheels). The drop in fatigue strength due to edge oxidation can also be compensated for by means of solidification processes (eg shot peening of gear wheels) of the components.

Aufgabe der vorliegenden Erfindung ist es nun, ein Verfahren zu entwickeln, das die Randoxidation wärmebehandelter Teile entfernt und die mechanische Bearbeitung ersetzt.The object of the present invention is now to develop a method which removes the edge oxidation of heat-treated parts and replaces the mechanical processing.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, daß zur thermochemischen Entfernung der infolge des ersten Verfahrensschritts erzeugten Randoxydation an den Bauteilen in einem zweiten Verfahrensschritt N₂, H₂ oder NH₃ oder ein Gemisch dieser Gase in die Prozeßkammer eingelassen und ein Druck größer 1 bar und eine Temperatur zwischen 100 °C und 1.000 °C voneinander unabhängig eingestellt wird.This object is achieved in that for the thermochemical removal of the edge oxidation generated as a result of the first process step on the components in a second process step N₂, H₂ or NH₃ or a mixture of these gases in the process chamber and a pressure greater than 1 bar and a temperature between 100 ° C and 1,000 ° C are set independently.

Die Oxide werden reduziert, indem sie mit der Gasphase reagieren und ihre Sauerstoffatome abgeben oder Nitride bilden. Solchermaßen wärmebehandelte Teile können je nach Zusammensetzung der Oxide nahezu vollkommen desoxidiert werden.
Eine solche Wärmebehandlung kann bei höher legierten Stählen als Ersatz für die ohnehin durchzuführende Anlaßbehandlung durchgeführt werden, Anlassen und Desoxidieren werden dann in einem Schritt durchgeführt.The oxides are reduced by reacting with the gas phase and releasing their oxygen atoms or forming nitrides. Depending on the composition of the oxides, parts heat-treated in this way can be almost completely deoxidized.
Such a heat treatment can be carried out for higher-alloy steels as a replacement for the tempering treatment which is to be carried out anyway, tempering and deoxidizing are then carried out in one step.

Durch dieses Verfahren ist es möglich, thermochemische Behandlungen mit oxidierenden Gaskomponenten weiter durchzuführen und durch die anschließende Desoxidation höhere Dauerfestigungseigenschaften an den Bauteilen zu erzielen. Dadurch kann auf den Einsatz teurer und komplizierter mechanischer Nachbehandlungen verzichtet werden.This process makes it possible to continue to carry out thermochemical treatments with oxidizing gas components and to achieve higher fatigue strength properties on the components through the subsequent deoxidation. As a result, the use of expensive and complicated mechanical post-treatments can be dispensed with.

Weitere Ausführungsmöglichkeiten und Merkmale sind in den Unteransprüchen näher beschrieben und gekennzeichnet.Further design options and features are described and characterized in more detail in the subclaims.

Die Erfindung läßt die verschiedensten Ausführungsmöglichkeiten zu; eine davon ist in den beiden anhängenden Skizzen beispielhaft dargestellt.The invention allows for a wide variety of designs; one of them is shown as an example in the two attached sketches.

Nachdem der Stahl in eine Behandlungskammer 1 eingebracht ist, wird diese auf 580 °C aufgeheizt und mit einem Druck von z.B. 10 bar wird H₂ und/oder NH₃ eingelassen. In diesem Verfahrensschritt wird der eingesetzte Stahl entpassiviert und gleichzeitig mit einer dünnen Nitridschicht als Schutz vor weiterer Oxidation versehen.After the steel has been introduced into a treatment chamber 1, it is heated to 580 ° C and at a pressure of e.g. 10 bar H₂ and / or NH₃ is let in. In this process step, the steel used is de-passivated and at the same time provided with a thin nitride layer as protection against further oxidation.

Anschließend wird der vor Oxidation geschützte Stahl in eine zweite Behandlungskammer 2 verbracht. Hier wird eine werkstoffspezifische Nitriertemperatur von 550 °C eingestellt und bei einem Druck von 1 bar ein Gasgemisch aus NH₃, H₂ eingelassen. Nach Abschluß dieses zweiten Behandlungsschrittes erhält man als Endprodukt einen nitrierten X 20 CrMo V 12 1- Stahl. Statt stickstoffhaltiger Gase können zum Kohlen auch kohlenstoffhaltige Gase wie CO₂ oder CO bei bei Temperaturen zwischen 800 °C und 1.000 °C eingesetzt werden.The steel, which is protected against oxidation, is then brought into a second treatment chamber 2. Here a material-specific nitriding temperature of 550 ° C is set and a gas mixture of NH₃, H₂ is let in at a pressure of 1 bar. After completing this second treatment step, a nitrided X 20 CrMo V 12 1 steel is obtained as the end product. Instead of nitrogen-containing gases, carbon-containing gases such as CO₂ or CO can be used for coal at temperatures between 800 ° C and 1,000 ° C.

Ein wesentlicher Vorteil ist, daß der eigentliche thermochemische Behandlungsvorgang, beispielsweise das Nitrieren in einer konventionellen Nitrieranlage unter Atmosphärendruck durchgeführt werden kann. Somit entfällt die Notwendigkeit eine Druckkammer einzusetzen, die beispielsweise für 30 bar ausgelegt sein muß.A major advantage is that the actual thermochemical treatment process, for example nitriding can be carried out in a conventional nitriding plant under atmospheric pressure. This eliminates the need to use a pressure chamber, which must be designed for 30 bar, for example.

Ein einsatzgehärteter Stahl 16 MnCr5 wird mit 10 »m Randoxidation in eine Prozeßkammer 1 eingebracht und auf eine Prozeßtemperatur ϑ = 200 °C erwärmt. In die Kammer wird nun ein Gasgemisch aus NH₃ und N₂ mit einem Druck p=20 bar eingelassen. Nach Abschluß dieses Prozesses erhält man einen randoxidationsfreien Stahl 16 MnCr5.A case-hardened steel 16 MnCr5 is introduced into a process chamber 1 with 10 »m edge oxidation and heated to a process temperature ϑ = 200 ° C. A gas mixture of NH₃ and N₂ with a pressure p = 20 bar is now let into the chamber. After completion of this process, 16 MnCr5 steel free of edge oxidation is obtained.

Claims (6)

  1. Method of treating components composed of steels and metals in a processing chamber under the actio of pressure and heat, comprising a first processing stage in which a thermochemical surface treatment, e.g. case-hardening, is carried out, to which end a gas or gas mixture is introduced into a processing chamber, characterised in that for the thermochemical removal of peripheral oxidation of the components, in a second processing stage N₂, H₂ or NH₃ or a mixture of these gases is introduced into the processing chamber, and a pressure of more than 1 bar and a temperature of between 100°C and 1 000°C are set independently of one another.
  2. Method according to claim 1, characterised in that components composed of unalloyed or low-alloy steels are treated.
  3. Method according to claim 1, characterised in that components composed of high-alloy steels are treated.
  4. Method according to claim 3, characterised in that simultaneously with the thermochemical removal of peripheral oxidation, a heat-treatment process, e.g. the annealing of steels, is carried out.
  5. Method according to one or more of claims 1 to 4, characterised in that the processing pressure during the process of thermochemically removing peripheral oxidation is 20 bar.
  6. Method according to claim 5, characterised in that the processing temperature is lower than or equal to the annealing temperature of the steel to be treated.
EP92118403A 1991-12-04 1992-10-27 Method of treating steel and refractory metals Expired - Lifetime EP0545069B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE4139975 1991-12-04
DE4139975A DE4139975C2 (en) 1991-12-04 1991-12-04 Process for the treatment of alloyed steels and refractory metals and application of the process
DE4208848A DE4208848C2 (en) 1991-12-04 1992-03-19 Process for the thermochemical after-treatment of steels and metals
DE4208848 1992-03-19

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EP0545069A1 EP0545069A1 (en) 1993-06-09
EP0545069B1 true EP0545069B1 (en) 1995-12-06

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JP (1) JPH0665631A (en)
AT (1) ATE131216T1 (en)
DE (2) DE4208848C2 (en)
ES (1) ES2080416T3 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
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

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0707661B1 (en) * 1994-04-22 2000-03-15 Innovatique S.A. Method of low pressure nitriding a metal workpiece and oven for carrying out said method
FR2719057B1 (en) * 1994-04-22 1996-08-23 Innovatique Sa Process for the nitriding at low pressure of a metallic part and oven for the implementation of said process.
DE10147205C1 (en) * 2001-09-25 2003-05-08 Bosch Gmbh Robert Process for the heat treatment of workpieces made of temperature-resistant steels
DE102009002985A1 (en) * 2009-05-11 2010-11-18 Robert Bosch Gmbh Process for carbonitriding

Citations (1)

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Publication number Priority date Publication date Assignee Title
EP0544987A1 (en) * 1991-12-04 1993-06-09 Leybold Durferrit GmbH Method of treating steel alloys and refractory metals

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Patent Citations (1)

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EP0544987A1 (en) * 1991-12-04 1993-06-09 Leybold Durferrit GmbH Method of treating steel alloys and refractory metals

Cited By (1)

* Cited by examiner, † Cited by third party
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

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ATE131216T1 (en) 1995-12-15
DE4208848C2 (en) 2001-08-30
DE59204598D1 (en) 1996-01-18
JPH0665631A (en) 1994-03-08
EP0545069A1 (en) 1993-06-09
DE4208848A1 (en) 1993-09-23
ES2080416T3 (en) 1996-02-01

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