WO2024037954A1 - Method for heat treating chrome steels - Google Patents

Method for heat treating chrome steels Download PDF

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Publication number
WO2024037954A1
WO2024037954A1 PCT/EP2023/072127 EP2023072127W WO2024037954A1 WO 2024037954 A1 WO2024037954 A1 WO 2024037954A1 EP 2023072127 W EP2023072127 W EP 2023072127W WO 2024037954 A1 WO2024037954 A1 WO 2024037954A1
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WIPO (PCT)
Prior art keywords
component
temperature
nitriding
gas
tempering
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PCT/EP2023/072127
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German (de)
French (fr)
Inventor
Stefan HANFF
Ralf Kuebler
Karl-Otto Englert
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Robert Bosch Gmbh
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Publication of WO2024037954A1 publication Critical patent/WO2024037954A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0043—Muffle furnaces; Retort furnaces
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C23C8/06—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
    • C23C8/10—Oxidising
    • 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
    • C23C8/80—After-treatment

Definitions

  • the present invention relates to a method for heat treating chromium steels, in particular high-alloy chromium-x steels, by gas nitriding and to a motor vehicle component resulting in particular from such a manufacturing process.
  • the field of application of the present invention extends primarily to automotive technology and tool making.
  • Motor vehicle components subject to wear and vibration made of high-alloy chromium steel i.e. a steel material with the main alloy component chromium, are usually tempered, activated and nitrided to achieve the desired component properties after the obligatory martensitic hardening.
  • high-alloy chromium steel such as X40CrMov5-l, X50CrMov5-l and
  • Low-alloy and high-alloy steels always have a naturally thin oxide layer of a few nanometers, which forms in a stable manner even at room temperature in normal air and/or different water vapor contents.
  • This oxide layer consists of the oxygen-affinous alloying elements chromium, molybdenum, vanadium, silicon, aluminum and iron as well as other alloying elements of the steel material that are capable of oxidation.
  • alloying elements are therefore no longer dissolved in the crystal lattice and, as a thin oxide layer, negatively or completely impair the diffusion of atomic nitrogen at the subsequent nitriding temperatures in the range between 400 to 600 ° C.
  • the result is inhomogeneous connecting layers and diffusion layers with undesirable different mechanical, electrical, magnetic and chemical functional properties.
  • these thin oxide layers are removed before the actual nitriding process chemically by pickling with an acid, electrically by applying an electrical voltage to open up the oxide layer or mechanically by surface processing by, for example, brushing, grinding or honing, or the like.
  • This intermediate processing step between tempering and subsequent nitriding requires a correspondingly high amount of production and time. In addition, there is no guarantee that all surface areas have been processed accordingly.
  • the core hardness of the component is adjusted according to the functional requirements through at least one tempering step via the tempering temperature.
  • the component is usually heated in a targeted manner in order to influence its properties, including to reduce workpiece stresses. It is the object of the present invention to create a heat treatment process for hardened chrome steels consisting of tempering and gas nitriding, in which the usual tempering and activation is eliminated and the core hardness of the component can be variably adjusted.
  • the object is achieved by a method for heat treatment according to claim 1.
  • the following dependent claims reflect advantageous developments of the invention.
  • the independent claim 10 specifies the product-by-process result of claim 1 for special motor vehicle components.
  • the invention includes the process engineering teaching that heat treatment of chromium steels, in particular high-alloy chromium-x steels, by gas nitriding includes the following process steps:
  • the advantage of the solution according to the invention is, in particular, that the functionally important core hardness of the material can now be freely adjusted independently of the nitriding temperature. As a result, the method according to the invention can be made usable for a broader application.
  • the solution according to the invention enables the core hardness to be adjusted independently of the required nitriding temperature. Because when nitriding between 480 - 600 °C, the core hardness only results between 620 HV1 - 460 HV1 according to the nitriding temperature. An independent choice of core hardness of, for example, 200 - 440 HV1 is not possible because nitriding above a material-specific limit leads to a functionally poor structure.
  • the pre-oxidation temperature of step (A) is chosen in the range between 300 to 450 ° C, preferably in the range between 350 to 450 ° C.
  • the range width results from the various material properties of the previously hardened steel component and is therefore dependent on its alloying elements. Tests have shown that the preferred range mentioned with a higher lower range limit for the pre-oxidation temperature offers higher energy efficiency, since the energy input for subsequent further heating after the tempering step is lower.
  • the pre-oxidation temperature is used according to the diffusion-permeable oxides to be formed. During heating, the nitrogen atmosphere prevents surface oxidation.
  • the tempering of step (B) should be started immediately after heating, i.e. when the pre-oxidation temperature is reached, but at the latest from a component temperature between 350 to 450 ° C with the most homogeneous possible temperature distribution in the oven.
  • the last-mentioned control parameter can be used to simplify the control of the temperature profile.
  • the pre-oxidation can be carried out via synthetic air, atmosphere or oxygen-containing gases.
  • the start of the tempering step is preferably effected by supplying a nitriding process gas after evacuation.
  • An oxygen-affinous process gas for example ammonia gas, ammonia gas-cracked gas mixture or the like, is suitable as the nitriding process gas.
  • Fission gas is a gas mixture that consists of the gases nitrogen and hydrogen. While During this tempering step it is irrelevant whether the temperature is kept constant or the temperature changes. However, from a critical process temperature of 450 to 550 ° C, the nitriding process gas can be removed via, for example, a vacuum process step as an intermediate step B1 or via a flushing process with nitrogen.
  • the component is further heated to the material-specific tempering temperature TA under preferably nitrogen or, depending on the tempering temperature, also under ammonia or cracked gas, with a holding time of at least one hour, preferably 2 to 4 hours, most preferably 3 +/- 0.5 hours is selected.
  • the duration of the holding time depends on the type of chrome steel to be heat-treated. Process gases or pure nitrogen are still supplied.
  • the component can preferably be heated in a conventional chamber furnace with a corresponding gas exchange device. After the tempering step in step C, the component is cooled to the nitriding temperature TN for gas nitriding. After passing through a material-specific cooling temperature, the nitrogen can, if necessary, be replaced by the nitriding process gas. After the nitriding temperature has been reached, the component is then gas nitrided in a conventional manner.
  • motor vehicle components in particular can be produced from a chrome steel, preferably a high-alloy chrome-x steel, which are particularly subject to wear and vibration.
  • These can be, for example, motor vehicle components such as nozzle bodies, valve pieces, valve plates, valve bodies, throttle plates, valve carriers or pistons, which are primarily used in the high-pressure area of the fuel supply of a motor vehicle.
  • Fig. 1 shows a flowchart of the method according to the invention for the heat treatment of chrome steels
  • Fig. 2 is a graphic representation of the temperature-time curve of the heat treatment according to Fig. 1.
  • the heat treatment according to the invention of an already hardened component made of chrome steel initially involves heating in a nitrogen atmosphere from ambient temperature Tu to a material-specific pre-oxidation temperature Tv of approximately 350 ° C.
  • the heating and the implementation of the subsequent process steps are carried out in a conventional chamber furnace, which is provided with a gas exchange device.
  • step B a starting frequency is started to start the heated component with the addition of a nitriding process gas, which in this exemplary embodiment is ammonia.
  • a nitriding process gas which in this exemplary embodiment is ammonia.
  • the ammonia is removed again in accordance with intermediate step B1. Further heating in step B1 is carried out up to the material-specific tempering temperature TA of above 550 ° C. In this exemplary embodiment, this tempering temperature is maintained for approximately 3 hours.
  • nitriding is initiated by cooling the component to its material-specific nitriding temperature in step D, so that gas nitriding begins. Then done in step E, the component is further cooled to the ambient temperature Tu.
  • step A of heating starting from the ambient temperature Tu
  • step B after the pre-oxidation, a tempering step is started with the addition of the process gas ammonia, whereby the pre-oxidation temperature Tv of approximately 400° resulting from the heating is initially maintained.
  • Tk critical process temperature
  • step B After a critical process temperature Tk of approximately 500 ° C is reached, the process gas ammonia is removed again in intermediate step B1 and cracking gas is introduced instead. Further heating takes place in step C to tempering temperature TA, which is maintained under a nitrogen atmosphere until time t « for approximately 3 hours until tempering is complete.
  • step D cooling to the nitriding temperature TN takes place again for gas nitriding in the presence of ammonia gas and cracked gas. After gas nitriding has been completed, the component is further cooled down to ambient temperature Tu in step E from time IN.
  • the invention is not limited to the preferred embodiment described above. Rather, modifications of this are also conceivable, which are included within the scope of protection of the following claims. For example, it is also possible to omit the intermediate step B1.
  • the specific temperatures in particular the pre-oxidation temperature Tv, the tempering temperature TA and the nitriding temperature TN, depend on the specific composition of the chrome steel to be heat-treated, i.e. in particular its alloying elements.

Abstract

The invention relates to a method for heat treating chrome steels, in particular high-alloy chrome x steels, by means of gas nitriding, comprising the following process steps: (A) heating a previously hardened component consisting of a chrome steel, under a nitrogen atmosphere, from an ambient temperature (tU) to its material-specific pre-oxidation temperature (tV) in order to carry out a pre-oxidation step; (B) carrying out at least one tempering step by adding a nitriding process gas to the nitrogen atmosphere around the component; (C) further heating the component to its material-specific tempering temperature (tA) and maintaining said temperature for at least one hour; (D) cooling the component to its material-specific nitriding temperature (tN) for gas nitriding of the component; and (E) further cooling the component to the ambient temperature (tU).

Description

Beschreibung Description
Titel: Title:
Verfahren zum Wärmebehandeln von Chromstählen Process for heat treating chrome steels
Die vorliegende Erfindung betrifft ein Verfahren zum Wärmebehandeln von Chromstählen, insbesondere hochlegierten Chrom-x-Stählen, durch Gas- Nitrieren sowie ein insbesondere aus einem solchen Herstellungsverfahren resultierendes Kraftfahrzeugbauteil. The present invention relates to a method for heat treating chromium steels, in particular high-alloy chromium-x steels, by gas nitriding and to a motor vehicle component resulting in particular from such a manufacturing process.
Das Einsatzgebiet der vorliegenden Erfindung erstreckt sich vornehmlich auf die Kraftfahrzeugtechnik sowie den Werkzeugbau. Verschleiß- und schwingungsbelastete Kraftfahrzeugbauteile aus hochlegiertem Chromstahl, also einem Stahlmaterial mit dem Hauptlegierungsbestandteil Chrom, werden gewöhnlich zur Erzielung der gewünschten Bauteileigenschaften nach dem obligatorischen martensitischen Härten angelassen, aktiviert und nitriert. Typischerweise bestehen derartige Bauteile aus speziell hochlegierten Chromstählen, wie beispielsweise X40CrMov5-l, X50CrMov5-l sowie X90CrW18 und werden im hier vornehmlich interessierenden Kraftfahrzeugtechnikbereich beispielsweise eingesetzt als Bauteile von Ventilen, Drosseln oder Kolben-Zylinder-Anordnungen in Hochdruckanwendungen. The field of application of the present invention extends primarily to automotive technology and tool making. Motor vehicle components subject to wear and vibration made of high-alloy chromium steel, i.e. a steel material with the main alloy component chromium, are usually tempered, activated and nitrided to achieve the desired component properties after the obligatory martensitic hardening. Typically, such components consist of specially high-alloy chromium steels, such as X40CrMov5-l, X50CrMov5-l and
Stand der Technik State of the art
Gemäß dem technischen Merkblatt „Wärmebehandlung von Stahl - Nitrieren und Nitrocarburieren“ (Herausgeber: Stahl-Informations-Zentrum Düsseldorf, Ausgabe 2005, ISSN 0175-2006) erfolgt das klassische Gas-Nitrieren von niedrig- und hochlegierten Stählen der hier interessierenden Art in mehreren Schritten. Es wird zunächst ein Härten, dann mehrere Anlasssequenzen bei meist unterschiedlichen Temperaturen und Zeiten, danach ein Aktivieren der Bauteiloberfläche als separater Prozess vor dem eigentlichen Nitrieren durchgeführt. Dabei können zwischen dem aus Härten und Anlassen bestehenden Vergütungsprozess und dem anschließenden Aktivier- und (Gas)- Nitrierprozess mehrere Stunden, Tage oder gar Wochen vergehen. According to the technical information sheet “Heat treatment of steel - nitriding and nitrocarburizing” (publisher: Stahl-Informations-Zentrum Düsseldorf, edition 2005, ISSN 0175-2006), the classic gas nitriding of low- and high-alloy steels of the type of interest here takes place in several steps . First there is hardening, then several tempering sequences at usually different temperatures and times, then activation of the component surface as a separate process before the actual nitriding carried out. Several hours, days or even weeks can pass between the hardening and tempering process and the subsequent activation and (gas) nitriding process.
Niedrig- und hochlegierte Stähle weisen stets eine natürliche dünne Oxidschicht von wenigen Nanometern auf, die sich an normaler Luft und/oder unterschiedlichen Wasserdampfgehalten auch schon bei Raumtemperatur stabil ausbildet. Diese Oxidschicht besteht aus den sauerstoffaffinen Legierungselementen Chrom, Molybdän, Vanadium, Silizium, Aluminium und Eisen sowie anderen oxidationsfähigen Legierungselementen des Stahlwerkstoffs. Low-alloy and high-alloy steels always have a naturally thin oxide layer of a few nanometers, which forms in a stable manner even at room temperature in normal air and/or different water vapor contents. This oxide layer consists of the oxygen-affinous alloying elements chromium, molybdenum, vanadium, silicon, aluminum and iron as well as other alloying elements of the steel material that are capable of oxidation.
Diese Legierungselemente sind somit nicht mehr im Kristallgitter gelöst und beeinträchtigen als dünne Oxidschicht ein Eindiffundieren von atomarem Stickstoff bei den anschließenden Nitriertemperaturen im Bereich zwischen 400 bis 600°C negativ bis vollständig. Inhomogene Verbindungsschichten sowie Diffusionsschichten mit nicht gewünschten unterschiedlichen mechanischen, elektrischen, magnetischen und chemischen funktionalen Eigenschaften sind die Folge. Gewöhnlich werden diese dünnen Oxidschichten vor dem eigentlichen Nitrierprozess chemisch über Beizen mit einer Säure, elektrisch über Anlegen einer elektrischen Spannung zum Aufschließen der Oxidschicht oder mechanisch über eine Oberflächenbearbeitung durch beispielsweise Bürsten, Schleifen oder Honen, oder dergleichen entfernt. Dieser Bearbeitungszwischenschritt zwischen dem Vergüten und einem anschließenden Nitrieren erfordert einen entsprechend hohen Fertigungs- und Zeitaufwand. Zusätzlich ist nicht sichergestellt, dass alle Oberflächenbereiche entsprechend bearbeitet wurden. These alloying elements are therefore no longer dissolved in the crystal lattice and, as a thin oxide layer, negatively or completely impair the diffusion of atomic nitrogen at the subsequent nitriding temperatures in the range between 400 to 600 ° C. The result is inhomogeneous connecting layers and diffusion layers with undesirable different mechanical, electrical, magnetic and chemical functional properties. Usually, these thin oxide layers are removed before the actual nitriding process chemically by pickling with an acid, electrically by applying an electrical voltage to open up the oxide layer or mechanically by surface processing by, for example, brushing, grinding or honing, or the like. This intermediate processing step between tempering and subsequent nitriding requires a correspondingly high amount of production and time. In addition, there is no guarantee that all surface areas have been processed accordingly.
Beim Gesamtprozess der Wärmebehandlung wird die Kernhärte des Bauteils entsprechend der funktionalen Anforderungen durch die mindestens einen Anlassschritt über die Anlasstemperatur eingestellt. Im Rahmen eines metallurgischen Anlassschritts wird das Bauteil gewöhnlich gezielt erwärmt, um seine Eigenschaften zu beeinflussen, auch um Werkstückspannungen abzubauen. Es ist die Aufgabe der vorliegenden Erfindung, ein aus Vergüten und Gas- Nitrieren bestehendes Wärmebehandlungsverfahren von gehärteten Chromstählen zu schaffen, bei dem das übliche Anlassen und Aktivieren entfällt und sich die Kernhärte des Bauteils variabel einstellen lässt. During the overall heat treatment process, the core hardness of the component is adjusted according to the functional requirements through at least one tempering step via the tempering temperature. As part of a metallurgical tempering step, the component is usually heated in a targeted manner in order to influence its properties, including to reduce workpiece stresses. It is the object of the present invention to create a heat treatment process for hardened chrome steels consisting of tempering and gas nitriding, in which the usual tempering and activation is eliminated and the core hardness of the component can be variably adjusted.
Offenbarung der Erfindung Disclosure of the invention
Die Aufgabe wird durch ein Verfahren zum Wärmebehandeln gemäß Anspruch 1 gelöst. Die nachfolgenden abhängigen Ansprüche geben vorteilhafte Weiterbildungen der Erfindung wieder. Der nebengeordnete Anspruch 10 spezifiziert das Product-by-Process-Resultat des Anspruchs 1 auf spezielle Kraftfahrzeugbauteile. The object is achieved by a method for heat treatment according to claim 1. The following dependent claims reflect advantageous developments of the invention. The independent claim 10 specifies the product-by-process result of claim 1 for special motor vehicle components.
Die Erfindung schließt die verfahrenstechnische Lehre ein, dass ein Wärmebehandeln von Chromstählen, insbesondere hochlegierten Chrom-x- Stählen, durch Gas-Nitrieren die folgenden Prozessschritte umfasst: The invention includes the process engineering teaching that heat treatment of chromium steels, in particular high-alloy chromium-x steels, by gas nitriding includes the following process steps:
(A) Aufheizen eines aus einem Chromstahl bestehenden zuvor gehärteten Bauteils unter Stickstoffatmosphäre von einer Umgebungstemperatur Tu auf dessen materialspezifische Voroxidationstemperatur Tv zur Durchführung eines Voroxidationsschritts; (A) heating a previously hardened component made of chrome steel under a nitrogen atmosphere from an ambient temperature Tu to its material-specific pre-oxidation temperature Tv in order to carry out a pre-oxidation step;
(B) Durchführung mindestens eines Anlassschritts unter Zugabe eines Nitrierprozessgases zur Stickstoffatmosphäre um das Bauteil; (B) carrying out at least one tempering step by adding a nitriding process gas to the nitrogen atmosphere around the component;
(C) weiteres Aufheizen des Bauteils auf dessen materialspezifischer Anlasstemperatur TA und Halten derselben über vorzugsweise mindestens eine Stunde; (C) further heating the component to its material-specific tempering temperature TA and holding it for preferably at least one hour;
(D) Abkühlen des Bauteils auf dessen materialspezifische Nitriertemperatur TN zum Gas-Nitrieren des Bauteils; und (D) cooling the component to its material-specific nitriding temperature TN for gas nitriding of the component; and
(E) weiteres Abkühlen des Bauteils auf die Umgebungstemperatur Tu. Der Vorteil der erfindungsgemäßen Lösung liegt insbesondere darin, dass die funktional wichtige Kernhärte des Werkstoffs nun unabhängig von der Nitriertemperatur frei eingestellt werden kann. Hierdurch kann das erfindungsgemäße Verfahren für eine breitere Anwendung nutzbar gemacht werden. Die erfindungsgemäße Lösung ermöglicht das Einstellen der Kernhärte unabhängig von der benötigten Nitriertemperatur. Denn beim Nitrieren zwischen 480 - 600 °C ergibt sich die Kernhärte nur zwischen 620 HV1 - 460 HV1 entsprechend der Nitriertemperatur. Eine unabhängige Wahl der Kernhärte von beispielsweise 200 - 440 HV1 ist nicht möglich, da das Nitrieren oberhalb einer werkstoffspezifischen Grenze zu funktional schlechtem Gefüge führt. (E) further cooling of the component to the ambient temperature Tu. The advantage of the solution according to the invention is, in particular, that the functionally important core hardness of the material can now be freely adjusted independently of the nitriding temperature. As a result, the method according to the invention can be made usable for a broader application. The solution according to the invention enables the core hardness to be adjusted independently of the required nitriding temperature. Because when nitriding between 480 - 600 °C, the core hardness only results between 620 HV1 - 460 HV1 according to the nitriding temperature. An independent choice of core hardness of, for example, 200 - 440 HV1 is not possible because nitriding above a material-specific limit leads to a functionally poor structure.
Vorzugsweise wird die Voroxidationstemperatur des Schritts (A) im Bereich zwischen 300 bis 450°C, vorzugsweise im Bereich zwischen 350 bis 450°C, gewählt. Die Bereichsbreite ergibt sich aus verschiedenen Materialeigenschaften des zuvor gehärteten Stahlbauteils und ist insoweit von dessen Legierungselementen abhängig. Versuche haben ergeben, dass der genannte Vorzugsbereich mit einer höheren unteren Bereichsgrenze für die Voroxidationstemperatur eine höhere Energieeffizienz bietet, da der Energieeintrag zum anschließenden weiteren Aufheizen nach dem Anlassschritt geringer ausfällt. Zusätzlich wird die Voroxidationstemperatur entsprechend den zu bildenden diffusiondurchlässigen Oxiden verwendet. Während des Aufheizens verhindert die Stickstoffatmosphäre eine Oberflächenoxidation. Preferably, the pre-oxidation temperature of step (A) is chosen in the range between 300 to 450 ° C, preferably in the range between 350 to 450 ° C. The range width results from the various material properties of the previously hardened steel component and is therefore dependent on its alloying elements. Tests have shown that the preferred range mentioned with a higher lower range limit for the pre-oxidation temperature offers higher energy efficiency, since the energy input for subsequent further heating after the tempering step is lower. In addition, the pre-oxidation temperature is used according to the diffusion-permeable oxides to be formed. During heating, the nitrogen atmosphere prevents surface oxidation.
Vorzugsweise sollte im direkten Anschluss an das Aufheizen das Anlassen des Schritts (B) gestartet werden, also ab Erreichen der Voroxidationstemperatur, jedoch spätestens ab einer Bauteiltemperatur zwischen 350 bis 450°C bei einer möglichst homogenen Temperaturverteilung im Ofen. Der letztgenannte Steuerungsparameter kann zur vereinfachten Steuerung des Temperaturverlaufs herangezogen werden. Die Voroxidation kann über synthetische Luft, Atmosphäre oder sauerstoffhaltige Gase durchgeführt werden. Der Start des Anlassschritts wird vorzugsweise dadurch bewirkt, dass nach dem Evakuieren ein Nitrierprozessgas zugeführt wird. Als Nitrierprozessgas eignet sich dafür ein sauerstoffaffines Prozessgas, beispielsweise Ammoniakgas, Ammoniakgas- Spaltgas-Gemisch oder dergleichen. Unter Spaltgas wird eine Gasmischung verstanden, die aus den Gasen Stickstoff und Wasserstoff besteht. Während dieses Anlassschritts ist es unerheblich, ob die Temperatur konstant gehalten wird oder sich aber die Temperatur ändert. Ab einer kritischen Prozesstemperatur von 450 bis 550°C kann jedoch das Nitrierprozessgas über beispielsweise einen Vakuumprozessschritt als Zwischenschritt Bl oder aber über einen Spülvorgang mit Stickstoff entfernt werden. Preferably, the tempering of step (B) should be started immediately after heating, i.e. when the pre-oxidation temperature is reached, but at the latest from a component temperature between 350 to 450 ° C with the most homogeneous possible temperature distribution in the oven. The last-mentioned control parameter can be used to simplify the control of the temperature profile. The pre-oxidation can be carried out via synthetic air, atmosphere or oxygen-containing gases. The start of the tempering step is preferably effected by supplying a nitriding process gas after evacuation. An oxygen-affinous process gas, for example ammonia gas, ammonia gas-cracked gas mixture or the like, is suitable as the nitriding process gas. Fission gas is a gas mixture that consists of the gases nitrogen and hydrogen. While During this tempering step it is irrelevant whether the temperature is kept constant or the temperature changes. However, from a critical process temperature of 450 to 550 ° C, the nitriding process gas can be removed via, for example, a vacuum process step as an intermediate step B1 or via a flushing process with nitrogen.
Im Anschluss an diesen Anlassschritt erfolgt ein weiteres Aufheizen des Bauteils auf die materialspezifische Anlasstemperatur TA unter vorzugsweise Stickstoff oder in Abhängigkeit der Anlasstemperatur auch unter Ammoniak oder Spaltgas, wobei eine Haltezeit von mindestens einer Stunde, vorzugsweise 2 bis 4 Stunden, ganz vorzugsweise 3 +/- 0,5 Stunden, gewählt wird. Die Dauer der Haltezeit ist wiederum abhängig von der Sorte des wärmezubehandelnden Chromstahls. Dabei werden weiterhin Prozessgase zugeführt oder aber reiner Stickstoff. Following this tempering step, the component is further heated to the material-specific tempering temperature TA under preferably nitrogen or, depending on the tempering temperature, also under ammonia or cracked gas, with a holding time of at least one hour, preferably 2 to 4 hours, most preferably 3 +/- 0.5 hours is selected. The duration of the holding time depends on the type of chrome steel to be heat-treated. Process gases or pure nitrogen are still supplied.
Das Aufheizen des Bauteils kann vorzugsweise in einem herkömmlichen Kammerofen mit entsprechender Gastauscheinrichtung durchgeführt werden. Nach dem Anlassschritt im Schritt C erfolgt das Abkühlen des Bauteils auf Nitriertemperatur TN zwecks Gas-Nitrieren. Nach dem Durchlaufen einer werkstoffspezifischen Abkühltemperatur kann der Stickstoff gegebenenfalls durch das Nitrierprozessgas ersetzt werden. Nach Erreichen der Nitriertemperatur erfolgt dann das Gas-Nitrieren des Bauteils in herkömmlicher Weise. The component can preferably be heated in a conventional chamber furnace with a corresponding gas exchange device. After the tempering step in step C, the component is cooled to the nitriding temperature TN for gas nitriding. After passing through a material-specific cooling temperature, the nitrogen can, if necessary, be replaced by the nitriding process gas. After the nitriding temperature has been reached, the component is then gas nitrided in a conventional manner.
Nach dem vorstehend beschriebenen Wärmebehandlungs-Verfahren lassen sich insbesondere Kraftfahrzeugbauteile aus einem Chromstahl, vorzugsweise einem hochlegierten Chrom-x-Stahl, herstellen, welche besonders verschleiß- und schwingungsbelastet sind. Dies können beispielsweise Kraftfahrzeugbauteile sein, wie Düsenkörper, Ventilstücke, Ventilplatten, Ventilkörper, Drosselplatten, Ventilträger oder Kolben, welche vornehmlich im Hochdruckbereich der Kraftstoffzuführung eines Kraftfahrzeugs zum Einsatz kommen. Figurenbeschreibung Using the heat treatment process described above, motor vehicle components in particular can be produced from a chrome steel, preferably a high-alloy chrome-x steel, which are particularly subject to wear and vibration. These can be, for example, motor vehicle components such as nozzle bodies, valve pieces, valve plates, valve bodies, throttle plates, valve carriers or pistons, which are primarily used in the high-pressure area of the fuel supply of a motor vehicle. Character description
Weitere die Erfindung verbessernde Maßnahmen werden nachstehend gemeinsam mit der Beschreibung eines bevorzugten Ausführungsbeispiels der Erfindung anhand der Figuren näher dargestellt. Es zeigt: Further measures improving the invention are shown in more detail below together with the description of a preferred exemplary embodiment of the invention with reference to the figures. It shows:
Fig. 1 einen Ablaufplan des erfindungsgemäßen Verfahrens zur Wärmebehandlung von Chromstählen, und Fig. 1 shows a flowchart of the method according to the invention for the heat treatment of chrome steels, and
Fig. 2 eine grafische Darstellung des Temperatur-Zeit-Verlaufs der Wärmebehandlung gemäß Fig. 1. Fig. 2 is a graphic representation of the temperature-time curve of the heat treatment according to Fig. 1.
Gemäß Fig. 1 beinhaltet das erfindungsgemäße Wärmebehandeln eines bereits gehärteten Bauteils aus Chromstahl zunächst in einem Schritt A ein Aufheizen unter Stickstoffatmosphäre von Umgebungstemperatur Tu auf eine materialspezifische Voroxidationstemperatur Tv von ca. 350°C. Das Aufheizen sowie die Durchführung der nachfolgenden Verfahrensschritte wird in einem herkömmlichen Kammerofen durchgeführt, welcher mit einer Gastauscheinrichtung versehen ist. 1, the heat treatment according to the invention of an already hardened component made of chrome steel initially involves heating in a nitrogen atmosphere from ambient temperature Tu to a material-specific pre-oxidation temperature Tv of approximately 350 ° C. The heating and the implementation of the subsequent process steps are carried out in a conventional chamber furnace, which is provided with a gas exchange device.
Nach dem Aufheizen und Voroxidieren erfolgt im Schritt B ein Starten einer Anlassfrequenz zum Anlassen des aufgeheizten Bauteils unter Zugabe eines Nitrierprozessgases, welches in diesem Ausführungsbeispiel Ammoniak ist. Ab Erreichen einer kritischen Prozesstemperatur wird gemäß dem Zwischenschritt Bl das Ammoniak wieder entfernt. Ein weiteres Aufheizen im Schritt Bl wird bis auf die materialspezifische Anlasstemperatur TA von oberhalb 550°C durchgeführt. Bei diesem Ausführungsbeispiel wird diese Anlasstemperatur über etwa 3 Stunden gehalten. After heating and pre-oxidation, in step B a starting frequency is started to start the heated component with the addition of a nitriding process gas, which in this exemplary embodiment is ammonia. Once a critical process temperature is reached, the ammonia is removed again in accordance with intermediate step B1. Further heating in step B1 is carried out up to the material-specific tempering temperature TA of above 550 ° C. In this exemplary embodiment, this tempering temperature is maintained for approximately 3 hours.
Nach dem Anlassen im Schritt C wird das Nitrieren dadurch eingeleitet, dass im Schritt D ein Abkühlen des Bauteils auf dessen materialspezifische Nitriertemperatur erfolgt, so dass ein Gas-Nitrieren einsetzt. Anschließend erfolgt im Schritt E ein weiteres Abkühlen des Bauteils auf die Umgebungstemperatur Tu. After tempering in step C, nitriding is initiated by cooling the component to its material-specific nitriding temperature in step D, so that gas nitriding begins. Then done in step E, the component is further cooled to the ambient temperature Tu.
Die Fig. 2 veranschaulicht einen Temperatur-Zeitverlauf des vorstehend beschriebenen Verfahrensablaufs, bei welchem im Schritt A des Aufheizens ausgehend von der Umgebungstemperatur Tu innerhalb einer beliebigen Aufheizzeit tA das Aufheizen des Bauteils unter Stickstoffatmosphäre durchgeführt wird. Anschließend wird im Schritt B nach dem Voroxidieren unter Zugabe des Prozessgases Ammoniak ein Anlassschritt gestartet, wobei zunächst die aus dem Aufheizen resultierende Voroxidationstemperatur Tv von ca. 400° aufrechterhalten bleibt. Ab Erreichen einer kritischen Prozesstemperatur Tk von ca. 500°C wird im Zwischenschritt Bl das Prozessgas Ammoniak wieder entfernt und stattdessen Spaltgas eingeleitet. Das weitere Aufheizen erfolgt im Schritt C auf Anlasstemperatur TA, welche unter Stickstoffatmosphäre bis zum Zeitpunkt t« über zirka 3 Stunden aufrechterhalten wird, bis das Anlassen abgeschlossen ist. Nachfolgend erfolgt im Schritt D wieder ein Abkühlen auf Nitriertemperatur TN zum Gas-Nitrieren unter Anwesenheit von Ammoniakgas und Spaltgas. Nach Abschluss des Gas-Nitrierens wird ab dem Zeitpunkt IN ein weiteres Abkühlen des Bauteils im Schritt E auf Umgebungstemperatur Tu durchgeführt. 2 illustrates a temperature-time profile of the process sequence described above, in which in step A of heating, starting from the ambient temperature Tu, the component is heated up under a nitrogen atmosphere within an arbitrary heating time tA. Subsequently, in step B, after the pre-oxidation, a tempering step is started with the addition of the process gas ammonia, whereby the pre-oxidation temperature Tv of approximately 400° resulting from the heating is initially maintained. Once a critical process temperature Tk of approximately 500 ° C is reached, the process gas ammonia is removed again in intermediate step B1 and cracking gas is introduced instead. Further heating takes place in step C to tempering temperature TA, which is maintained under a nitrogen atmosphere until time t« for approximately 3 hours until tempering is complete. Subsequently, in step D, cooling to the nitriding temperature TN takes place again for gas nitriding in the presence of ammonia gas and cracked gas. After gas nitriding has been completed, the component is further cooled down to ambient temperature Tu in step E from time IN.
Die Erfindung ist nicht beschränkt auf das vorstehend beschriebene bevorzugte Ausführungsbeispiel. Es sind vielmehr auch Abwandlungen hiervon denkbar, welche vom Schutzbereich der nachfolgenden Ansprüche mit umfasst sind. So ist es beispielsweise auch möglich, den Zwischenschritt Bl wegzulassen. Die konkreten Temperaturen, insbesondere die Voroxidationstemperatur Tv, die Anlasstemperatur TA sowie die Nitriertemperatur TN, richten sich nach der konkreten Zusammensetzung des wärmezubehandelnden Chromstahls, also insbesondere dessen Legierungselemente. The invention is not limited to the preferred embodiment described above. Rather, modifications of this are also conceivable, which are included within the scope of protection of the following claims. For example, it is also possible to omit the intermediate step B1. The specific temperatures, in particular the pre-oxidation temperature Tv, the tempering temperature TA and the nitriding temperature TN, depend on the specific composition of the chrome steel to be heat-treated, i.e. in particular its alloying elements.

Claims

Ansprüche Expectations
1. Verfahren zum Wärmebehandeln von Chromstählen, insbesondere hochlegierten Chrom-x-Stählen, durch Gas-Nitrieren, umfassend die folgenden Prozessschritte: 1. Process for heat treating chrome steels, in particular high-alloy chrome-x steels, by gas nitriding, comprising the following process steps:
(A) Aufheizen eines aus einem Chromstahl bestehenden zuvor gehärteten Bauteils unter Stickstoffatmosphäre von einer Umgebungstemperatur (Tu) auf dessen materialspezifische Voroxidationstemperatur (Tv) zur Durchführung einer Voroxidationsschritts; (A) heating a previously hardened component made of chrome steel under a nitrogen atmosphere from an ambient temperature (Tu) to its material-specific pre-oxidation temperature (Tv) in order to carry out a pre-oxidation step;
(B) Durchführung mindestens eines Anlassschritts unter Zugabe eines Nitrierprozessgases zur Stickstoffatmosphäre um das Bauteil; (B) carrying out at least one tempering step by adding a nitriding process gas to the nitrogen atmosphere around the component;
(C) Weiteres Aufheizen des Bauteils auf dessen materialspezifische Anlasstemperatur (TA) und Halten derselben über eine Haltedauer; (C) further heating the component to its material-specific tempering temperature (TA) and maintaining it for a holding period;
(D) Abkühlen des Bauteils auf dessen materialspezifische Nitriertemperatur (TN) zum Gas-Nitrieren des Bauteils; (D) cooling the component to its material-specific nitriding temperature (TN) for gas nitriding of the component;
(E) Weiteres Abkühlen des Bauteils auf die Umgebungstemperatur (Tu). (E) Further cooling of the component to the ambient temperature (Tu).
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Voroxidationstemperatur (Tv) des Schrittes (A) im Bereich zwischen 300°C bis 450°C, vorzugsweise im Bereich zwischen 350°C bis 450°C, eingestellt wird. 2. The method according to claim 1, characterized in that the pre-oxidation temperature (Tv) of step (A) is set in the range between 300°C to 450°C, preferably in the range between 350°C to 450°C.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die direkt im Anschluss an das Aufheizen gestartete Anlassschritt im Schritt (B) ab Erreichen der Voroxidationstemperatur, jedoch spätestens ab einer Bauteiltemperatur zwischen 350°C bis 450°C beginnt. 3. The method according to claim 1, characterized in that the tempering step in step (B), which is started directly after the heating, begins when the pre-oxidation temperature is reached, but at the latest from a component temperature between 350 ° C to 450 ° C.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Nitrierprozessgas ausgewählt ist aus einer Gruppe von sauerstoffaffinen Prozessgasen, umfassend: Ammoniakgas, Ammoniakgas-Spaltgas-Gemisch. 4. The method according to claim 1, characterized in that the nitriding process gas is selected from a group of oxygen-affinous process gases, comprising: ammonia gas, ammonia gas-cracked gas mixture.
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass im Schritt (B) das Nitrierprozessgas ab Erreichen einer kritischen Prozesstemperatur von 450°C bis 550°C in einem Zwischenschritt (Bl) entfernt oder durch reinen Stickstoff ersetzt wird. 5. The method according to claim 1, characterized in that in step (B) the nitriding process gas is removed or replaced by pure nitrogen in an intermediate step (B1) once a critical process temperature of 450 ° C to 550 ° C has been reached.
6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das weitere Aufheizen des Bauteils im Schritt (C) auf eine Anlasstemperatur zwischen 550°C bis 700°C durchgeführt wird. 6. The method according to claim 1, characterized in that the further heating of the component in step (C) is carried out to a tempering temperature between 550 ° C and 700 ° C.
7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Haltezeit der Anlasstemperatur im Schritt (C) mindestens 1 Stunde, vorzugsweise zwischen 2 bis 4 Stunden, ganz vorzugsweise 3 +/- 0,5 Stunden beträgt. 7. The method according to claim 1, characterized in that the holding time of the tempering temperature in step (C) is at least 1 hour, preferably between 2 to 4 hours, most preferably 3 +/- 0.5 hours.
8. Verfahren nach Anspruch 1, dadurch gekennzeichnet, das Bauteil einen Massenanteil von mindestens 2% Chrom als Legierungsmetall enthält. 8. The method according to claim 1, characterized in that the component contains a mass fraction of at least 2% chromium as an alloy metal.
9. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass das Aufheizen des Bauteils in einem Kammerofen mit Gastauscheinrichtung durchgeführt wird. 9. The method according to claim 1, characterized in that the heating of the component is carried out in a chamber furnace with a gas exchange device.
10. Kraftfahrzeugbauteil aus einem Chromstahl, insbesondere einem hochlegierten Chrom-x-Stahl, das nach einem Herstellungsverfahren nach einem der vorstehenden Ansprüche vergütet ist. 10. Motor vehicle component made of a chrome steel, in particular a high-alloy chrome-x steel, which is tempered according to a manufacturing process according to one of the preceding claims.
11. Bauteil nach Anspruch 10, dadurch gekennzeichnet, dass dieses ausgewählt ist aus einer Gruppe von verschleiß- und schwingungsbelasteten Kraftfahrzeugbauteilen, umfassend Düsenkörper, Ventilstück, Ventilplatte, Ventilkörper, Drosselplatte, Ventilträger, Kolben. 11. Component according to claim 10, characterized in that it is selected from a group of motor vehicle components subject to wear and vibration, comprising nozzle body, valve piece, valve plate, valve body, throttle plate, valve carrier, piston.
PCT/EP2023/072127 2022-08-15 2023-08-10 Method for heat treating chrome steels WO2024037954A1 (en)

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Citations (2)

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US20170138326A1 (en) * 2014-07-11 2017-05-18 Robert Bosch Gmbh Method for nitriding a component of a fuel injection system
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DE102018208283A1 (en) * 2018-05-25 2019-11-28 Robert Bosch Gmbh Method for producing a metallic component

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