EP1432841B1 - Method for heat-treating work pieces made of temperature-resistant steels - Google Patents

Method for heat-treating work pieces made of temperature-resistant steels Download PDF

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Publication number
EP1432841B1
EP1432841B1 EP02776699A EP02776699A EP1432841B1 EP 1432841 B1 EP1432841 B1 EP 1432841B1 EP 02776699 A EP02776699 A EP 02776699A EP 02776699 A EP02776699 A EP 02776699A EP 1432841 B1 EP1432841 B1 EP 1432841B1
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EP
European Patent Office
Prior art keywords
process according
workpiece
nitriding
atmosphere
temperature
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EP02776699A
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German (de)
French (fr)
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EP1432841A2 (en
Inventor
Nils Lippmann
Wolfgang Lerche
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Robert Bosch GmbH
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Robert Bosch GmbH
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/02—Pretreatment of the material to be coated

Definitions

  • the present application relates to a method for heat treatment of a workpiece made of temperature-resistant steels, in particular of hot-work steels, wherein the workpiece is hardened and nitrided after mechanical processing and electrochemical treatment and wherein a reduction of the workpiece surface is carried out during curing without a pickling treatment before the subsequent nitriding must be performed.
  • DE 3 633 490 discloses a rotor made of a steel alloy for a ring spinning machine.
  • DE 1 933 439 discloses a nitriding process with two basic process steps.
  • US 6,168,095 discloses a fuel injector for internal combustion engines with a nozzle body.
  • Nozzle bodies for modern DI injection systems are increasingly being used at working temperatures up to 450 ° C. Accordingly, high demands are placed on the component strength and the wear resistance of the nozzle body.
  • For the production of the nozzle body in particular nitrided hot working steels are therefore used.
  • In the production of internal bores (pressure chamber) and for the rounding ECM procedures (Electro Chemical Maschining, electrochemical metalworking) are used.
  • the ECM processes which are used for shaping and surface treatment of metallic workpieces, are used in an electrolyte solution performed, wherein the workpiece to be machined is usually connected as the anode and the tool as a cathode.
  • the electrochemical metal working methods are used in particular for deburring, polishing, grinding and etching the surfaces of a workpiece.
  • the surfaces resulting from the ECM process are largely passive and can only be treated very poorly by thermal-chemical diffusion methods, in particular nitriding, since more noble alloying elements such as Cr remain on the surface or oxidize alloying elements, with metal oxides and metal hydroxides Me x O y [OH] z are formed.
  • the passive surfaces are currently pickled prior to nitriding, especially using hydrochloric acid.
  • the pickling suffers from considerable disadvantages.
  • stigmata may be produced.
  • the results of the pickling can be reproduced very poorly, since, for example, the storage time between processing, heat treatment and nitriding can be different lengths.
  • Pickling also creates significant additional costs, particularly due to the cost of the equipment used for pickling and the labor costs required.
  • the stained workpieces must be cleaned after pickling using a very complex special cleaning technology. The disposal of pickling solutions is expensive.
  • the pickling with acid to an undesirable burden on the environment and worsens the working conditions.
  • the technical problem underlying the present invention is therefore to develop a method for the treatment of workpieces made of hot-work steels, in particular DI nozzle bodies, that in particular improves the nitridability of these workpieces without the need to pickle the workpieces, and therefore the stand known in the art, caused by the pickling disadvantages are avoided.
  • the present invention solves the underlying technical problem by providing a method for producing a workpiece from a temperature-resistant steel, in particular hot-work steel, wherein the workpiece is hardened and thereby de-passivated, characterized in that the hardening step comprises a reduction treatment, in particular by means of hydrogen and nitriding the quenched workpieces with the more active surface in different steps under different gas atmospheres is then carried out, the nitriding initially under an atmosphere of ammonia and an oxidizing agent, in particular water vapor or air, and then under an atmosphere of ammonia and a carbon-containing gas , in particular endogas or a mixture with CO and / or CO 2 , is performed.
  • the hardening step comprises a reduction treatment, in particular by means of hydrogen and nitriding the quenched workpieces with the more active surface in different steps under different gas atmospheres is then carried out, the nitriding initially under an atmosphere of ammonia and an oxidizing agent, in particular water vapor or air, and
  • the method according to the invention is also considerably less expensive than the methods known in the prior art since the systems required for pickling and subsequent cleaning are eliminated and only devices for supplying hydrogen to the vacuum hardening system are required. Since no acids are used for pickling in the process according to the invention, this also leads to a significant relief of the environment, in particular to an improvement in working conditions.
  • the workpiece is hardened from a temperature-resistant steel, in particular from hot-work steel, and thereby de-passivated, the hardening step comprising a reduction treatment.
  • the reduction removes the metal oxide and / or metal hydroxide layers present on the surface of the workpiece, so that the subsequent nitriding is considerably improved without the need for pickling.
  • the reduction treatment is carried out using hydrogen.
  • a hot-work steel is understood to mean a steel which, during its use, is constantly exposed to an elevated temperature, in particular a temperature of more than 200 ° C. During use, no structural changes may occur in hot-work steel, but the structure must be sufficiently stable and resistant to attack. Depending on the desired use, hot working steels must have different properties. Important desired properties are in particular hardness and strength, which in turn determine the wear resistance.
  • Hot work tool steels must meet some special performance requirements, such as hot strength, especially achieved by molybdenum, tungsten and grain fine vanadium, tempering resistance produced by chromium, which together with molybdenum, nickel and manganese enhances hardenability, and hot wear resistance the heat resistance of the matrix and by the type and amount of special carbides is determined.
  • hot strength especially achieved by molybdenum, tungsten and grain fine vanadium
  • tempering resistance produced by chromium which together with molybdenum, nickel and manganese enhances hardenability
  • hot wear resistance the heat resistance of the matrix and by the type and amount of special carbides is determined.
  • DI nozzle bodies made of hot-work steel must have a very high wear resistance.
  • the workpiece made of a temperature-resistant steel, in particular hot-work steel, machined before curing and an electrochemical Processing, ie, running in electrolyte solution ECM process for shaping and surface treatment.
  • electrochemical Processing ie, running in electrolyte solution ECM process for shaping and surface treatment.
  • the workpiece in particular deburred, polished; be ground and / or etched.
  • internal bores can be produced with an ECM process, which are subsequently rounded.
  • the workpiece is subjected to a cleaning step in an aqueous cleaning medium, in particular a neutral cleaner.
  • the cleaning step according to the invention prevents the formation of thick Me x O y [OH] z layers on the surface of the workpiece.
  • the workpiece is dried. Subsequently, the workpiece can be hardened immediately.
  • the workpiece if it is to be stored for a longer period after ECM processing, first conserved using suitable methods and after storage, immediately before curing, again cleaned in a liquid cleaning medium ,
  • the curing which leads to a structural change of the hot-work steel described above, takes place in a single-chamber or multi-chamber vacuum furnace.
  • the hardening involves first a convective heating of the workpiece under nitrogen.
  • the convective heating of the workpiece is carried out under a nitrogen pressure of more than 0.8 bar.
  • the workpiece can also be heated in a vacuum.
  • the workpiece is heated at least up to the hardening temperature of the hot working steel.
  • the hardening temperature of hot-work steel is around 1040 ° C.
  • the nitrogen atmosphere or the vacuum is replaced by hydrogen.
  • the introduced hydrogen which serves as a reducing agent for reducing the metal oxide and / or metal hydroxide layers present on the tool surface, is introduced according to the invention at a temperature of at least 400.degree.
  • the temperatures at which hydrogen is introduced are in the range of the hardening temperature.
  • the hydrogen partial pressure is about 1 to 100 mbar.
  • the flow rate for the hydrogen to be added is 100 to 2000 Nl / h.
  • the austenitization is preferably carried out over a period of 10 to 40 minutes.
  • the gas exchange takes place pulsating over a period of 1 to 10 minutes. That is, the pressure build-up of the hydrogen partial pressure is pulsed over a period of 1 to 10 minutes in exchange with vacuum. In this way, a better gas exchange, especially for workpieces with blind holes, achieved according to the invention.
  • the hydrogen is pumped off before ending the austenitization in order to avoid contamination of the gas used in the subsequent quenching step with hydrogen.
  • the quenching of the austenitized workpiece in nitrogen at a pressure of 1 to 10 bar is carried out after holding to hardening temperature.
  • the workpiece is subjected to at least one annealing step.
  • the workpiece is tempered at a temperature of up to 650 ° C, wherein the tempering of the workpieces takes place either in a nitrogen atmosphere or under a nitrogen-hydrogen atmosphere.
  • a nitrogen-hydrogen atmosphere this contains up to 5% hydrogen.
  • the tempering of the workpiece takes place in a vacuum oven or an evacuatable tempering furnace. The annealing step according to the invention is carried out for about 1 to 2 hours.
  • the workpiece is subjected to not only one but several annealing steps.
  • the workpiece is a first annealing step, which takes about 1 to 2 hours and is heated to a temperature of 520 ° C, and then subjected to a second annealing step, which also takes about 1 to 2 hours and wherein is heated to a temperature of 610 ° C, subjected.
  • the workpiece is nitrided immediately after tempering.
  • the nitriding leads to a hardening of the hot working steel, from which the workpiece consists. This is due to a diffusion of nitrogen into the steel. This leads to the incorporation of nitrogen on interstitial sites and formation of nitrides and nitrogen deposition on carbides to form carbonitrides. Nitriding produces hard surface layers which increase the hardness, wear resistance and fatigue strength of the hot work tool steel.
  • the workpiece is transferred immediately after curing and tempering in a nitriding.
  • the nitriding furnace used in accordance with the invention is preferably a purged chamber furnace or an evacuable retort furnace.
  • the oxidizing agent used in step 1 is preferably 0.5 to 10% by volume of water vapor or up to 15% of air.
  • the carbon support used in step 2 is preferably 1 to 10% by volume of endogas. Endogas, which is obtained by endothermic reaction of hydrocarbons, such as propane, is a mixture of 23.7 vol .-% CO, 31.5 vol .-% H 2 and 44.8 vol .-% N 2 . In a further preferred embodiment, CO and / or CO 2 in equivalent proportions can also be used as carbon carriers.
  • the nitriding in step 2 is referred to as gas oxycarbouration and, according to the invention, lasts more than 4 hours, preferably about 10 to 60 hours.
  • Gasoxicarburleiters reaction which lasts longer than four hours according to the invention, already has a uniform nitriding on formed the surface of the workpiece.
  • a treatment under ammonia or a gas additive to reduce the nitriding characteristic takes place in order to limit the connection layer growth.
  • the flow rate of the gases during the nitriding is dependent on the volume of the furnace space and is preferably three times the volume of the furnace space in Nl / h.
  • the workpieces are cooled after nitriding using nitrogen.
  • the workpiece treated and produced using the method of the invention may then be hard worked using conventional methods.
  • the inventive method can be used in particular for the production of temperature-resistant DI nozzle body made of hot working steels, wherein the nozzle body made of high-strength and temperature-resistant hot working steels, in particular the steel brands X40CrMoV51 and X38CrMoV51.
  • the pressure chamber is further processed in a production cycle comprising the soft machining, ECM processing and subsequent directly concatenated cleaning in an aqueous cleaning medium, but according to the invention, no pickling treatment is carried out.
  • the DI nozzle body in a vacuum oven in the temperature range between 1000 ° C and 1070 ° C under a pulsed hydrogen partial pressure of 1 to 100 mbar hardened and then quenched in a nitrogen gas stream at a pressure of 1 to 10 bar.
  • the annealing is carried out at a temperature of up to 650 ° C in a nitrogen or nitrogen-hydrogen atmosphere.
  • the subsequent nitration is preferably carried out at 510 to 590 ° C for a period of 10 to 60 hours using the above-described gas oxinitrocarburization process in a chamber furnace or evacuable retort furnace.
  • treated heat-resistant DI nozzle body have more favorable consolidation properties, since the nitriding layer is uniform and accounts for the Beiznarben described in the prior art.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Heat Treatment Of Articles (AREA)

Description

Die vorliegende Anmeldung betrifft ein Verfahren zur Wärmebehandlung eines Werkstücks aus temperaturbeständigen Stählen, insbesondere aus Warmarbeitsstählen, wobei das Werkstück nach mechanischer Bearbeitung und elektrochemischer Behandlung gehärtet und nitriert wird und wobei beim Härten eine Reduktion der Werkstückoberfläche durchgeführt wird, ohne dass vor dem nachfolgenden Nitrieren eine Beizbehandlung durchgeführt werden muss.The present application relates to a method for heat treatment of a workpiece made of temperature-resistant steels, in particular of hot-work steels, wherein the workpiece is hardened and nitrided after mechanical processing and electrochemical treatment and wherein a reduction of the workpiece surface is carried out during curing without a pickling treatment before the subsequent nitriding must be performed.

DE 3 633 490 offenbart ein Läufer aus einer Stahllegierung für eine Ringspinnmaschine. DE 3 633 490 discloses a rotor made of a steel alloy for a ring spinning machine.

DE 1 933 439 offenbart ein Nitrierverfahren mit zwei grundsätzlichen Verfahrensschritten. DE 1 933 439 discloses a nitriding process with two basic process steps.

US 6 168 095 offenbart ein Kraftstoffeinspritzdüse für Brennkraftmaschinen mit einem Düsenkorper. US 6,168,095 discloses a fuel injector for internal combustion engines with a nozzle body.

Düsenkörper für moderne DI-Einspritzsysteme werden in zunehmendem Maße bei Arbeitstemperaturen bis zu 450°C eingesetzt. Dementsprechend werden hohe Anforderungen an die Bauteilfestigkeit und den Verschleißwiderstand der Düsenkörper gestellt. Zur Herstellung der Düsenkörper werden daher insbesondere nitrierte Warmarbeitsstähle verwendet. Bei der Herstellung von Innenbohrungen (Druckkammer) und für das Verrunden kommen ECM-Verfahren (Electro Chemical Maschining; elektrochemische Metallbearbeitung) zur Anwendung. Die ECM-Verfahren, die zur Formgebung und Oberflächenbehandlung von metallischen Werkstücken dienen, werden in einer Elektrolyt-Lösung durchgeführt, wobei das zu bearbeitende Werkstück meist als Anode und das Werkzeug als Kathode geschaltet ist. Die elektrochemischen Metallbearbeitungsverfahren werden insbesondere zum Entgraten, Polieren, Schleifen und Ätzen der Oberflächen eines Werkstücks benutzt. Die durch das ECM-Verfahren entstehenden Oberflächen sind weitestgehend passiv und lassen sich nur sehr schlecht durch thermisch-chemische Diffusionsverfahren behandeln, insbesondere nitrieren, da edlere Legierungselemente wie beispielsweise Cr an der Oberfläche.verbleiben beziehungsweise Legierungselemente oxidieren, wobei Metalloxide und Metallhydroxide MexOy[OH]z gebildet werden.Nozzle bodies for modern DI injection systems are increasingly being used at working temperatures up to 450 ° C. Accordingly, high demands are placed on the component strength and the wear resistance of the nozzle body. For the production of the nozzle body, in particular nitrided hot working steels are therefore used. In the production of internal bores (pressure chamber) and for the rounding ECM procedures (Electro Chemical Maschining, electrochemical metalworking) are used. The ECM processes, which are used for shaping and surface treatment of metallic workpieces, are used in an electrolyte solution performed, wherein the workpiece to be machined is usually connected as the anode and the tool as a cathode. The electrochemical metal working methods are used in particular for deburring, polishing, grinding and etching the surfaces of a workpiece. The surfaces resulting from the ECM process are largely passive and can only be treated very poorly by thermal-chemical diffusion methods, in particular nitriding, since more noble alloying elements such as Cr remain on the surface or oxidize alloying elements, with metal oxides and metal hydroxides Me x O y [OH] z are formed.

Zur Verbesserung der Nitrierbarkeit von DI-Düsenkörpern werden die passiven Oberflächen derzeit vor dem Nitrieren gebeizt, insbesondere unter Verwendung von Salzsäure. Das Beizen ist jedoch mit erheblichen Nachteilen behaftet. Beim Beizen mit Säure können Beiznarben entstehen. Dadurch bedingt, verringert sich die Bauteilfestigkeit. Ferner lassen sich die Ergebnisse des Beizens nur sehr schlecht reproduzieren, da beispielsweise die Lagerdauer zwischen Bearbeitung, Grundwärmebehandlung und Nitrieren unterschiedlich lang sein kann. Durch das Beizen entstehen ferner erhebliche Zusatzkosten, die insbesondere auf die Kosten für die zum Beizen verwendete Anlage und die erforderlichen Arbeitskosten zurückgehen. Auch müssen die gebeizten Werkstücke nach dem Beizen unter Verwendung einer sehr aufwendigen Spezial-Reinigungstechnik gereinigt werden. Die Entsorgung von Beizlösungen ist aufwendig. Darüber hinaus führt das Beizen mit Säure zu einer unerwünschten Belastung der Umwelt und verschlechtert die Arbeitsbedingungen.To improve the nitridability of DI nozzle bodies, the passive surfaces are currently pickled prior to nitriding, especially using hydrochloric acid. The pickling, however, suffers from considerable disadvantages. When stained with acid, stigmata may be produced. As a result, the component strength is reduced. Furthermore, the results of the pickling can be reproduced very poorly, since, for example, the storage time between processing, heat treatment and nitriding can be different lengths. Pickling also creates significant additional costs, particularly due to the cost of the equipment used for pickling and the labor costs required. Also, the stained workpieces must be cleaned after pickling using a very complex special cleaning technology. The disposal of pickling solutions is expensive. In addition, the pickling with acid to an undesirable burden on the environment and worsens the working conditions.

Das der vorliegenden Erfindung zugrunde liegende technische Problem besteht also darin, ein Verfahren zur Behandlung von Werkstücken aus Warmarbeitsstählen, insbesondere DI-Düsenkörpern, zu entwickeln, dass insbesondere die Nitrierbarkeit dieser Werkstücke verbessert, ohne dass die Werkstücke gebeizt werden müssen, und daher die im Stand der Technik bekannten, durch das Beizen bedingten Nachteile vermieden werden.The technical problem underlying the present invention is therefore to develop a method for the treatment of workpieces made of hot-work steels, in particular DI nozzle bodies, that in particular improves the nitridability of these workpieces without the need to pickle the workpieces, and therefore the stand known in the art, caused by the pickling disadvantages are avoided.

Die vorliegende Erfindung löst das ihr zugrunde liegende technische Problem durch die Bereitstellung eines Verfahrens zur Herstellung eines Werkstücks aus einem temperaturbeständigen Stahl, insbesondere Warmarbeitsstahl, wobei das Werkstück gehärtet und dadurch entpassiviert wird, dadurch gekennzeichnet, dass der Härteschritt eine Reduktionsbehandlung, insbesondere mittels Wasserstoff, umfasst und erfindungsgemäß dann das Nitrieren der vergüteten Werkstücke mit der aktiveren Oberfläche in mehreren Schritten unter unterschiedlichen Gasatmosphären durchgeführt wird, wobei die Nitrierung zunächst unter einer Atmosphäre aus Ammoniak und einem Oxidationsmittel, insbesondere Wasserdampf oder Luft, und anschließend unter einer Atmosphäre aus Ammoniak und einem kohlenstoffhaltigen Gas, insbesondere Endogas oder einem Gemisch mit CO und/oder CO2, durchgeführt wird.The present invention solves the underlying technical problem by providing a method for producing a workpiece from a temperature-resistant steel, in particular hot-work steel, wherein the workpiece is hardened and thereby de-passivated, characterized in that the hardening step comprises a reduction treatment, in particular by means of hydrogen and nitriding the quenched workpieces with the more active surface in different steps under different gas atmospheres is then carried out, the nitriding initially under an atmosphere of ammonia and an oxidizing agent, in particular water vapor or air, and then under an atmosphere of ammonia and a carbon-containing gas , in particular endogas or a mixture with CO and / or CO 2 , is performed.

Die Vorteile des erfindungsgemäßen Verfahrens zur Wärmebehandlung und der damit hergestellten temperaturbeständigen Werkstücke aus Wärmearbeitstahl, insbesondere DI-Düsenkörpern, resultieren insbesondere aus dem Wegfall der Beizbehandlung vor dem Nitrieren. Da erfindungsgemäß kein Beizen vorgesehen ist, können auch keine Beiznarben auf der Oberfläche des Werkstücks entstehen. Dadurch bedingt, weisen die so hergestellten Werkstücke sehr vorteilhafte Festigkeitseigenschaften aus. Da das erfindungsgemäße Verfahren die Nitrierbarkeit der Werkstücks-Oberflächen erheblich verbessert, zeichnen sich die Werkstücke darüber hinaus durch äußerst gleichmäßige Nitrierschichten im gesamten Innen- und Außenbereich aus. Das erfindungsgemäße Verfahren ist gegenüber den im Stand der Technik bekannten Verfahren auch wesentlich kostengünstiger, da die zum Beizen und nachfolgenden Reinigen erforderlichen Anlagen entfallen und nur noch Vorrichtungen zur Wasserstoffversorgung an der Vakuum-Härteanlage benötigt werden. Da im erfindungsgemäßen Verfahren keine Säuren zum Beizen eingesetzt werden, führt dies auch zu einer deutlichen Entlastung der Umwelt, insbesondere auch zu einer Verbesserung der Arbeitsbedingungen.The advantages of the method according to the invention for the heat treatment and the temperature-resistant produced therewith Workpieces made of heat treated steel, in particular DI nozzle bodies, result in particular from the omission of the pickling treatment before nitriding. Since according to the invention no pickling is provided, no pickling scars can also be formed on the surface of the workpiece. As a result, the workpieces produced in this way have very advantageous strength properties. Moreover, since the process of the present invention significantly improves the nitridability of the workpiece surfaces, the workpieces are characterized by extremely uniform nitriding layers throughout the interior and exterior. The method according to the invention is also considerably less expensive than the methods known in the prior art since the systems required for pickling and subsequent cleaning are eliminated and only devices for supplying hydrogen to the vacuum hardening system are required. Since no acids are used for pickling in the process according to the invention, this also leads to a significant relief of the environment, in particular to an improvement in working conditions.

Erfindungsgemäß ist also vorgesehen, dass das Werkstück aus einem temperaturbeständigen Stahl, insbesondere aus Warmarbeitsstahl, gehärtet und und dabei entpassiviert wird, wobei der Härteschritt eine Reduktionsbehandlung umfasst. Durch die Reduktion werden die auf der Oberfläche des Werkstücks befindlichen Metalloxid- und/oder Metallhydroxid-Schichten entfernt, so dass das anschließende Nitrieren erheblich verbessert wird, ohne dass ein Beizen durchgeführt werden muss. Erfindungsgemäß besonders bevorzugt erfolgt die Reduktionsbehandlung unter Verwendung von Wasserstoff.According to the invention, it is thus provided that the workpiece is hardened from a temperature-resistant steel, in particular from hot-work steel, and thereby de-passivated, the hardening step comprising a reduction treatment. The reduction removes the metal oxide and / or metal hydroxide layers present on the surface of the workpiece, so that the subsequent nitriding is considerably improved without the need for pickling. According to the invention more preferably, the reduction treatment is carried out using hydrogen.

Im Zusammenhang mit der vorliegenden Erfindung wird unter einem Warmarbeitsstahl ein Stahl verstanden, der während seiner Verwendung ständig einer erhöhten Temperatur, insbesondere einer Temperatur von mehr als 200°C, ausgesetzt ist. Während der Verwendung dürfen im Warmarbeitsstahl keine Gefügeänderungen auftreten, sondern das Gefüge muss hinreichend stabil und anlassbeständig sein. Je nach gewünschter Verwendung müssen Warmarbeitsstähle unterschiedliche Eigenschaften aufweisen. Wichtige gewünschte Eigenschaften sind insbesondere Härte und Festigkeit, die ihrerseits die Verschleißbeständigkeit bestimmen.In the context of the present invention, a hot-work steel is understood to mean a steel which, during its use, is constantly exposed to an elevated temperature, in particular a temperature of more than 200 ° C. During use, no structural changes may occur in hot-work steel, but the structure must be sufficiently stable and resistant to attack. Depending on the desired use, hot working steels must have different properties. Important desired properties are in particular hardness and strength, which in turn determine the wear resistance.

Warmarbeitsstähle müssen einige spezielle Anforderungen bezüglich Gebrauchseigenschaften erfüllen, wie Warmfestigkeit, die insbesondere durch- Molybän, Wolfram und kornfeinendes Vanadium erreicht wird, Anlassbeständigkeit, die durch Chrom erzeugt wird, das zusammen mit Molybdän, Nickel und Mangan die Härtbarkeit erhöht, und Warmverschleißwiderstand, der durch die Warmfestigkeit der Matrix sowie durch Art und Menge der Sonderkarbide bestimmt wird. DI-Düsenkörper aus Warmarbeitsstahl müssen beispielsweise einen sehr hohen Verschleißwiderstand aufweisen.Hot work tool steels must meet some special performance requirements, such as hot strength, especially achieved by molybdenum, tungsten and grain fine vanadium, tempering resistance produced by chromium, which together with molybdenum, nickel and manganese enhances hardenability, and hot wear resistance the heat resistance of the matrix and by the type and amount of special carbides is determined. For example, DI nozzle bodies made of hot-work steel must have a very high wear resistance.

In einer bevorzugten Ausführungsform der Erfindung kann das Werkstück aus einem temperaturbeständigen Stahl, insbesondere Warmarbeitsstahl, vor dem Härten mechanisch bearbeitet und einer elektrochemischen Bearbeitung unterworfen werden, also einem in Elektrolytlösung ablaufenden ECM-Verfahren zur Formgebung und Oberflächenbehandlung. Unter Anwendung eines solchen Verfahrens kann das Werkstück insbesondere entgratet, poliert; geschliffen und/oder geätzt werden. Beispielsweise lassen sich mit einem ECM-Verfahren Innenbohrungen herstellen, die anschließend verrundet werden.In a preferred embodiment of the invention, the workpiece made of a temperature-resistant steel, in particular hot-work steel, machined before curing and an electrochemical Processing, ie, running in electrolyte solution ECM process for shaping and surface treatment. Using such a method, the workpiece in particular deburred, polished; be ground and / or etched. For example, internal bores can be produced with an ECM process, which are subsequently rounded.

Erfindungsgemäß ist vorgesehen, dass nach dem ECM-Verfahren das Werkstück einem Reinigungsschritt in einem wässrigen Reinigungsmedium, insbesondere einem Neutralreiniger unterzogen wird. Der erfindungsgemäße Reinigungsschritt verhindert die Ausbildung dicker MexOy[OH]z-Schichten auf der Oberfläche des Werkstückes. Im Anschluss an den Reinigungsschritt wird das Werkstück getrocknet. Anschließend kann das Werkstück sofort gehärtet werden. In einer Ausführungsform der Erfindung ist vorgesehen, dass das Werkstück, wenn es nach der ECM-Bearbeitung über einen längeren Zeitraum gelagert werden soll, zunächst unter Verwendung geeigneter Verfahren konserviert und nach der Lagerung, unmittelbar vor dem Härten, nochmals in einem flüssigen Reinigungsmedium gereinigt wird.According to the invention, it is provided that, according to the ECM method, the workpiece is subjected to a cleaning step in an aqueous cleaning medium, in particular a neutral cleaner. The cleaning step according to the invention prevents the formation of thick Me x O y [OH] z layers on the surface of the workpiece. After the cleaning step, the workpiece is dried. Subsequently, the workpiece can be hardened immediately. In one embodiment of the invention it is provided that the workpiece, if it is to be stored for a longer period after ECM processing, first conserved using suitable methods and after storage, immediately before curing, again cleaned in a liquid cleaning medium ,

Erfindungsgemäß ist vorgesehen, dass das Härten, das zu einer vorstehend beschriebenen Strukturveränderung des Warmarbeitsstahls führt, in einem Ein- oder Mehrkammer-Vakuumofen erfolgt. Das Härten umfasst zunächst ein konvektives Erwärmen des Werkstückes unter Stickstoff. Vorzugsweise erfolgt das konvektive Erwärmen des Werkstückes unter einem Stickstoffdruck von mehr als 0,8 bar. In einer anderen Ausführungsform der Erfindung kann das Werkstück auch im Vakuum erwärmt werden. Erfindungsgemäß ist vorgesehen, dass das Werkstück mindestens bis zur Härtetemperatur des Warmarbeitsstahles erwärmt wird. Die Härtetemperatur von Warmarbeitsstahl liegt bei etwa 1040°C.According to the invention, it is provided that the curing, which leads to a structural change of the hot-work steel described above, takes place in a single-chamber or multi-chamber vacuum furnace. The hardening involves first a convective heating of the workpiece under nitrogen. Preferably, the convective heating of the workpiece is carried out under a nitrogen pressure of more than 0.8 bar. In another Embodiment of the invention, the workpiece can also be heated in a vacuum. According to the invention, it is provided that the workpiece is heated at least up to the hardening temperature of the hot working steel. The hardening temperature of hot-work steel is around 1040 ° C.

Erfindungsgemäß ist vorgesehen, dass nach Erreichen einer gewünschten Temperatur die Stickstoffatmosphäre oder das Vakuum durch Wasserstoff ersetzt wird. Der eingeleitete Wasserstoff, der als Reduktionsmittel zur Reduktion der auf der Werkzeugoberfläche vorhandenen Metalloxid- und/oder Metallhydroxid-Schichten dient, wird erfindungsgemäß bei einer Temperatur von mindestens 400°C eingeleitet. Vorzugsweise liegen die Temperaturen, bei denen Wasserstoff eingeleitet wird, jedoch im Bereich der Härtetemperatur. Erfindungsgemäß beträgt der Wasserstoffteildruck etwa 1 bis 100 mbar. Vorzugsweise beträgt die Durchflussmenge für den zuzugebenden Wasserstoff 100 bis 2000 Nl/h. Die Austenitisierung wird vorzugsweise über einen Zeitraum von 10 bis 40 Minuten durchgeführt.According to the invention it is provided that after reaching a desired temperature, the nitrogen atmosphere or the vacuum is replaced by hydrogen. The introduced hydrogen, which serves as a reducing agent for reducing the metal oxide and / or metal hydroxide layers present on the tool surface, is introduced according to the invention at a temperature of at least 400.degree. Preferably, however, the temperatures at which hydrogen is introduced are in the range of the hardening temperature. According to the invention, the hydrogen partial pressure is about 1 to 100 mbar. Preferably, the flow rate for the hydrogen to be added is 100 to 2000 Nl / h. The austenitization is preferably carried out over a period of 10 to 40 minutes.

In einer besonders bevorzugten Ausführungsform der Erfindung erfolgt der Gasaustausch pulsierend über einen Zeitraum von 1 bis 10 Minuten. Das heißt, der Druckaufbau des Wasserstoffteildruckes erfolgt pulsierend über einen Zeitraum von 1 bis 10 Minuten im Austausch mit Vakuum. Auf diese Weise wird erfindungsgemäß ein besserer Gasaustausch, insbesondere bei Werkstücken mit Sacklochbohrungen, erreicht.In a particularly preferred embodiment of the invention, the gas exchange takes place pulsating over a period of 1 to 10 minutes. That is, the pressure build-up of the hydrogen partial pressure is pulsed over a period of 1 to 10 minutes in exchange with vacuum. In this way, a better gas exchange, especially for workpieces with blind holes, achieved according to the invention.

Erfindungsgemäß ist vorgesehen, dass vor dem Beenden der Austenitisierung der Wasserstoff abgepumpt wird, um eine Verunreinigung des im nachfolgenden Schritt zum Abschrecken eingesetzten Gases mit Wasserstoff zu vermeiden.According to the invention, it is provided that the hydrogen is pumped off before ending the austenitization in order to avoid contamination of the gas used in the subsequent quenching step with hydrogen.

Erfindungsgemäß erfolgt im Anschluss an das Halten auf Härtetemperatur das Abschrecken des austenitisierten Werkstückes in Stickstoff mit einem Druck von 1 bis 10 bar.According to the invention, the quenching of the austenitized workpiece in nitrogen at a pressure of 1 to 10 bar is carried out after holding to hardening temperature.

Erfindungsgemäß ist vorgesehen, dass nach dem Härten, insbesondere nach dem Abschrecken, das Werkstück mindestens einem Anlassschritt unterworfen wird.According to the invention, after hardening, in particular after quenching, the workpiece is subjected to at least one annealing step.

Erfindungsgemäß ist insbesondere vorgesehen, dass das Werkstück bei einer Temperatur von bis zu 650°C angelassen wird, wobei das Anlassen der Werkstücke entweder in einer Stickstoffatmosphäre oder unter einer Stickstoff-Wasserstoff-Atmosphäre erfolgt. Bei Verwendung einer Stickstoff-Wasserstoff-Atmosphäre enthält diese bis zu 5% Wasserstoff. Erfindungsgemäß ist vorgesehen, dass das Anlassen des Werkstückes in einem Vakuumofen oder einem evakuierbaren Anlassofen erfolgt. Der erfindungsgemäße Anlassschritt wird etwa 1 bis 2 Stunden durchgeführt.According to the invention it is provided in particular that the workpiece is tempered at a temperature of up to 650 ° C, wherein the tempering of the workpieces takes place either in a nitrogen atmosphere or under a nitrogen-hydrogen atmosphere. When using a nitrogen-hydrogen atmosphere, this contains up to 5% hydrogen. According to the invention, it is provided that the tempering of the workpiece takes place in a vacuum oven or an evacuatable tempering furnace. The annealing step according to the invention is carried out for about 1 to 2 hours.

Erfindungsgemäß besteht die Möglichkeit, dass das Werkstück nicht nur einem, sondern mehreren Anlasschritten unterworfen wird. In einer besonders bevorzugten Ausführungsform wird das Werkstück einem ersten Anlassschritt, der etwa 1 bis 2 Stunden dauert und wobei auf eine Temperatur von 520°C erwärmt wird, und im Anschluss daran einem zweiten Anlassschritt, der ebenfalls etwa 1 bis 2 Stunden dauert und wobei auf eine Temperatur von 610°C erwärmt wird, unterworfen.According to the invention there is the possibility that the workpiece is subjected to not only one but several annealing steps. In a particularly preferred embodiment, the workpiece is a first annealing step, which takes about 1 to 2 hours and is heated to a temperature of 520 ° C, and then subjected to a second annealing step, which also takes about 1 to 2 hours and wherein is heated to a temperature of 610 ° C, subjected.

Erfindungsgemäß ist vorgesehen, dass das Werkstück unmittelbar nach dem Anlassen nitriert wird. Die Nitrierung führt zu einer Härtung des Warmarbeitsstahls, aus dem das Werkstück besteht. Dies beruht auf einer Diffusion von Stickstoff in den Stahl. Dabei kommt es zur Einlagerung von Stickstoff auf Zwischengitterplätze und Bildung von Nitriden sowie zur Stickstoff-Anlagerung an Karbide unter Bildung von Karbonitriden. Durch die Nitrierung werden harte Randschichten erzeugt, wodurch die Härte, der Verschleißwiderstand und die Dauerfestigkeit des Warmarbeitsstahles erhöht werden.According to the invention, it is provided that the workpiece is nitrided immediately after tempering. The nitriding leads to a hardening of the hot working steel, from which the workpiece consists. This is due to a diffusion of nitrogen into the steel. This leads to the incorporation of nitrogen on interstitial sites and formation of nitrides and nitrogen deposition on carbides to form carbonitrides. Nitriding produces hard surface layers which increase the hardness, wear resistance and fatigue strength of the hot work tool steel.

Erfindungsgemäß ist vorgesehen, dass das Werkstück nach Härten und Anlassen sofort in einen Nitrierofen überführt wird. Bei dem erfindungsgemäß verwendeten Nitrierofen handelt es sich vorzugsweise um einen gespülten Kammerofen oder einen evakuierbaren Retortenofen.According to the invention it is provided that the workpiece is transferred immediately after curing and tempering in a nitriding. The nitriding furnace used in accordance with the invention is preferably a purged chamber furnace or an evacuable retort furnace.

In einer besonders bevorzugten Ausführungsform der Erfindung werden die Werkstücke in dem Nitrierofen in einem ersten Schritt von Raumtemperatur bis zu einer Temperatur von etwa 400°C erwärmt. Das Erwärmen der Werkstücke im Nitrierofen erfolgt dabei vorzugsweise unter einer Ammoniakatmosphäre. Danach wird das Werkstück in einem zweiten Schritt bis zur Nitriertemperatur, die etwa zwischen 500°C und 600°C liegt, erwärmt. Das im Anschluss an das Erwärmen durchgeführte Nitrieren der Werkstücke umfasst erfindungsgemäß die folgenden Schritte:

Schritt 1:
Nitrieren unter einer Atmosphäre aus Ammoniak und einem Oxidationsmittel,
Schritt 2:
Nitrieren unter einer Atmosphäre aus Ammoniak und einem Kohlenstoffträger, und
Schritt 3:
Nitrieren unter einer Atmosphäre aus Ammoniak oder einem Gaszusatz zur Verringerung der Nitrierkennzahl.
In a particularly preferred embodiment of the invention, the workpieces are heated in the nitriding oven in a first step from room temperature to a temperature of about 400 ° C. The heating of the workpieces in the nitriding oven is preferably carried out under an ammonia atmosphere. Thereafter, the workpiece is in a second step up to the nitriding temperature, which is approximately between 500 ° C and 600 ° C, heated. The nitriding of the workpieces carried out after the heating comprises according to the invention the following steps:
Step 1:
Nitriding under an atmosphere of ammonia and an oxidizing agent,
Step 2:
Nitriding under an atmosphere of ammonia and a carbon carrier, and
Step 3:
Nitriding under an atmosphere of ammonia or a gas additive to reduce the nitriding index.

Das heißt, die Nitrierung des Werkstückes erfolgt unter einem schrittweisen Wechsel der verwendeten Gasatmosphäre. Als Oxidationsmittel in Schritt 1 werden vorzugsweise 0,5 bis 10 Vol.-% Wasserdampf oder bis zu 15% Luft eingesetzt. Bei dem in Schritt 2 verwendeten Kohlenstoffträger handelt es sich vorzugsweise um 1 bis 10 Vol.-% Endogas. Endogas, das durch endotherme Umsetzung von Kohlenwasserstoffen, beispielsweise Propan, gewonnen wird, ist ein Gemisch aus 23,7 Vol.-% CO, 31,5 Vol.-% H2 und 44,8 Vol.-% N2. In einer weiteren bevorzugten Ausführungsform können auch CO und/oder CO2 in äquivalenten Anteilen als Kohlenstoffträger verwendet werden. Das Nitrieren in Schritt 2 wird als Gasoxicarburieren bezeichnet und dauert erfindungsgemäß mehr als 4 Stunden, vorzugsweise etwa 10 bis 60 Stunden. Nach der Gasoxicarburierungs-Reaktion, die erfindungsgemäß länger als vier Stunden dauert, hat sich bereits eine gleichmäßige Nitrierschicht auf der Oberfläche des Werkstückes ausgebildet. Im Anschluss an Schritt 2, also in Schritt 3, erfolgt erfindungsgemäß eine Behandlung unter Ammoniak oder einem Gaszusatz zur Verringerung der Nitrierkennzahl, um das Verbindungsschichtwachstum einzuschränken.That is, the nitriding of the workpiece is carried out under a step change of the gas atmosphere used. The oxidizing agent used in step 1 is preferably 0.5 to 10% by volume of water vapor or up to 15% of air. The carbon support used in step 2 is preferably 1 to 10% by volume of endogas. Endogas, which is obtained by endothermic reaction of hydrocarbons, such as propane, is a mixture of 23.7 vol .-% CO, 31.5 vol .-% H 2 and 44.8 vol .-% N 2 . In a further preferred embodiment, CO and / or CO 2 in equivalent proportions can also be used as carbon carriers. The nitriding in step 2 is referred to as gas oxycarbouration and, according to the invention, lasts more than 4 hours, preferably about 10 to 60 hours. After Gasoxicarburierungs reaction, which lasts longer than four hours according to the invention, already has a uniform nitriding on formed the surface of the workpiece. Subsequent to step 2, that is to say in step 3, according to the invention, a treatment under ammonia or a gas additive to reduce the nitriding characteristic takes place in order to limit the connection layer growth.

Die Durchflussmenge der Gase während der Nitrierung ist vom Volumen des Ofennutzraumes abhängig und beträgt vorzugsweise das dreifache des Volumens des Ofennutzraumes in Nl/h.The flow rate of the gases during the nitriding is dependent on the volume of the furnace space and is preferably three times the volume of the furnace space in Nl / h.

Erfindungsgemäß ist es vorgesehen, dass die Werkstücke nach Nitrieren unter Verwendung von Stickstoff abgekühlt werden. Das unter Verwendung des erfindungsgemäßen Verfahrens behandelte und hergestellte Werkstück kann danach unter Anwendung üblicher Verfahren hart bearbeitet werden.According to the invention, it is provided that the workpieces are cooled after nitriding using nitrogen. The workpiece treated and produced using the method of the invention may then be hard worked using conventional methods.

Das erfindungsgemäße Verfahren kann insbesondere zur Herstellung temperaturbeständiger DI-Düsenkörper aus Warmarbeitsstählen eingesetzt werden, wobei die Düsenkörper aus hochfesten und temperaturbeständigen Warmarbeitsstählen, insbesondere den Stahlmarken X40CrMoV51 und X38CrMoV51 hergestellt werden. Die Druckkammer wird in einem Fertigungszyklus, umfassend die Weichbearbeitung, ECM-Bearbeitung und nachfolgende direkt verkettete Reinigung in einem wässrigen Reinigungsmedium, weiter bearbeitet, wobei jedoch erfindungsgemäß keine Beizbehandlung durchgeführt wird. Anschließend werden die DI-Düsenkörper im Vakuumofen im Temperaturbereich zwischen 1000°C und 1070°C unter einem gepulsten Wasserstoff-Teildruck von 1 bis 100 mbar gehärtet und anschließend in einem Stickstoff-Gasstrom bei einem Druck von 1 bis 10 bar abgeschreckt. Das Anlassen erfolgt bei einer Temperatur von bis zu 650°C in einer Stickstoff- oder Stickstoff-Wasserstoffatmosphäre. Die anschließende Nitrierung erfolgt vorzugsweise bei 510 bis 590°C über einen Zeitraum von 10 bis 60 Stunden unter Verwendung des vorstehend beschriebenen Gasoxinitrocarburierungs-Verfahrens in einem Kammerofen oder evakuierbaren Retortenofen. So behandelte warmfeste DI-Düsenkörper weisen günstigere Festigungseigenschaften auf, da die Nitrierschicht gleichmäßig ausgebildet ist und die im Stand der Technik beschriebenen Beiznarben entfallen.The inventive method can be used in particular for the production of temperature-resistant DI nozzle body made of hot working steels, wherein the nozzle body made of high-strength and temperature-resistant hot working steels, in particular the steel brands X40CrMoV51 and X38CrMoV51. The pressure chamber is further processed in a production cycle comprising the soft machining, ECM processing and subsequent directly concatenated cleaning in an aqueous cleaning medium, but according to the invention, no pickling treatment is carried out. Subsequently, the DI nozzle body in a vacuum oven in the temperature range between 1000 ° C and 1070 ° C under a pulsed hydrogen partial pressure of 1 to 100 mbar hardened and then quenched in a nitrogen gas stream at a pressure of 1 to 10 bar. The annealing is carried out at a temperature of up to 650 ° C in a nitrogen or nitrogen-hydrogen atmosphere. The subsequent nitration is preferably carried out at 510 to 590 ° C for a period of 10 to 60 hours using the above-described gas oxinitrocarburization process in a chamber furnace or evacuable retort furnace. Thus treated heat-resistant DI nozzle body have more favorable consolidation properties, since the nitriding layer is uniform and accounts for the Beiznarben described in the prior art.

Weitere vorteilhafte Ausgestaltungen der Erfindung ergeben sich aus den Unteransprüchen.Further advantageous embodiments of the invention will become apparent from the dependent claims.

Claims (34)

  1. Process for producing a workpiece from a thermally stable steel, in particular from hot-work steel, wherein the workpiece is hardened and nitrided, characterized in that the hardening step comprises a reduction treatment and forms a depassivated surface for the stepped nitriding.
  2. Process according to Claim 1, characterized in that the reducing agent used is hydrogen.
  3. Process according to Claim 1 or 2, characterized in that the workpiece is machined and electrochemically treated prior to the hardening step.
  4. Process according to one of the preceding claims, characterized in that the workpiece is cleaned prior to the hardening step.
  5. Process according to Claim 4, characterized in that the workpiece is cleaned in an aqueous cleaning medium.
  6. Process according to one of the preceding claims, characterized in that the workpiece is dried following the cleaning operation.
  7. Process according to one of the preceding claims, characterized in that the hardening step comprises the convective heating of the workpiece under a nitrogen atmosphere or in vacuo.
  8. Process according to Claim 7, characterized in that the convective heating takes place at a nitrogen pressure of more than 0.8 bar.
  9. Process according to Claim 7 or 8, characterized in that the workpiece is heated at least to the hardening temperature of the hot-work steel.
  10. Process according to one of Claims 7 to 9, characterized in that after the desired temperature has been reached the nitrogen atmosphere or the vacuum is replaced by a hydrogen atmosphere.
  11. Process according to Claim 10, characterized in that the hydrogen atmosphere is generated in pulsed fashion over a pulsation duration of from 1 to 10 minutes.
  12. Process according to Claim 10 or 11, characterized in that the hydrogen has a partial pressure of from 1 to 100 mbar.
  13. Process according to one of Claims 10 to 12, characterized in that the quantitative flow of hydrogen is from 100 to 2000 1/h (s.t.p.).
  14. Process according to one of Claims 7 to 13, characterized in that the hardening step is carried out in a single-chamber or multi-chamber vacuum furnace.
  15. Process according to one of Claims 7 to 14, characterized in that the workpiece is quenched after the hardening operation.
  16. Process according to Claim 15, characterized in that the workpiece is quenched using nitrogen.
  17. Process according to Claim 15 or 16, characterized in that the nitrogen has a pressure of from 1 to 10 bar.
  18. Process according to one of the preceding claims, characterized in that a tempering step is carried out after the hardening operation.
  19. Process according to Claim 18, characterized in that the tempering step comprises heating the workpiece up to a temperature of 650ºC.
  20. Process according to Claim 18 or 19, characterized in that the workpiece is heated under a nitrogen atmosphere.
  21. Process according to Claim 18 or 19, characterized in that the workpiece is heated under a nitrogen/hydrogen atmosphere with a hydrogen content of up to 5%.
  22. Process according to one of Claims 18 to 21, characterized in that the tempering is carried out in a vacuum furnace or a tempering furnace that can be evacuated.
  23. Process according to one of Claims 18 to 22, characterized in that the tempering is carried out over a period of from 1 to 4 hours.
  24. Process according to one of the preceding claims, characterized in that the workpiece is treated by means of nitriding.
  25. Process according to Claim 24, characterized in that the workpiece is heated from room temperature up to a temperature of approximately 400ºC in a first step.
  26. Process according to Claim 25, characterized in that the workpiece is heated under an ammonia atmosphere.
  27. Process according to one of Claims 24 to 26, characterized in that the workpiece is heated up to the nitriding temperature.
  28. Process according to one of Claims 24 to 27, characterized in that the nitriding of the workpiece comprises the following steps:
    Step 1: Nitriding under an atmosphere comprising ammonia and an oxidizing agent,
    Step 2: Nitriding under an atmosphere comprising ammonia and a carbon carrier, and
    Step 3: Nitriding under an atmosphere comprising ammonia or a gas addition used to reduce the nitriding potential.
  29. Process according to Claim 28, characterized in that the oxidizing agent used is from 0.5 to 10% by volume water vapour or up to 15% air.
  30. Process according to Claim 28 or 29, characterized in that the carbon carrier used is from 1 to 10% by volume endothermic gas or CO and CO2 in equivalent proportions.
  31. Process according to one of the preceding claims, characterized in that after nitriding the workpiece is cooled under nitrogen.
  32. Process according to one of the preceding claims, characterized in that the workpiece is hard-worked after cooling.
  33. Process according to one of the preceding claims, characterized in that the workpiece is a DI nozzle body.
  34. DI nozzle body, characterized in that it has been produced using a process according to one of Claims 1 to 33.
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JP2005503488A (en) 2005-02-03
EP1432841A2 (en) 2004-06-30
DE10147205C1 (en) 2003-05-08
BR0206051B1 (en) 2011-02-08
BR0206051A (en) 2003-09-23
WO2003027349A3 (en) 2003-12-04
US7108756B2 (en) 2006-09-19
US20040055670A1 (en) 2004-03-25
WO2003027349A2 (en) 2003-04-03

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