Skip to content
  2. Research
  3. Scientific Departments
  4. Materials Engineering
  5. Heat Treatment

The properties of metallic materials can be changed by a specific heat treatment and adapted to the increasing demands of stress. With this aim in mind, the department of heat treatment is engaged in application-oriented, technical-scientific and scientific research projects with questions arising in connection with thermal and thermochemical heat treatments. Examples are process developments for saving energy and operating resources or for the improvement of component and material properties.

The competences of the department of heat treatment include both surface layer and penetrating processes and cover both purely thermal heat treatment and thermochemical heat treatment. In the department's own hardening shop, a wide range of furnaces on a technical scale are available for research and development. Many of the scientific questions are dealt with in a transfer-oriented manner in order to ensure a rapid transfer of new findings from research to industrial practice.

Range of topics of the department in the field of stress oriented heat treatment processes.

Further research focuses besides process development are the development and testing of process-accompanying monitoring and control systems, quenching technology as well as dimensional and shape changes during heat treatment. The experimental work is supported by heat treatment simulation and calculations.

In addition to project-related research, the department offers support for industry in the development of adapted heat treatment processes for specific property profiles of the components as well as support for problems with dimensional and shape changes and damage analyses.

Contract Services

Our department supports companies in the selection, design and implementation of heat treatment processes as well as in the investigation of heat-treated components. In addition to technical consulting, we offer application-oriented heat treatments, inductive heat treatment and failure analysis. Our services include, among others:

  • Consulting on material selection, heat treatment processes, process control and component properties, as well as support in the design and optimisation of heat treatment processes
  • Induction hardening of components using medium- and high-frequency processes, including multi-frequency processes for the targeted generation of different hardness profiles
  • General heat treatment of metallic components and specimens, including carburising and carbonitriding, case hardening and various nitriding processes
  • Failure analysis with a focus on heat treatment, including the investigation of damage to components and specimens as well as expert assessment activities

Detailed information on our services can be found in the Services section, in particular under Modelling and Simulation, Material Processing and Modification, Material Testing and Characterisation and Damage Analysis.

Contact us to learn more and to discuss how we can support your project.

Heat treatment activities are organized in four work areas

The activities in the main fields are organised in the four working areas"Case Hardening", "Induction Hardening", "Sensor Technology and Nitriding" and "Simulation and Ashing Technology". In the following, the main topics are presented.

Case Hardening

Case hardening is the process of choice for the treatment of highly stressed components, such as gears. A prerequisite for reliable process control is knowledge of the processes and their sequences, i.e. the thermodynamic laws of reactions in the gas atmosphere and in the edge layer of the workpiece. In this context, the use of suitable measuring and control methods is of great importance.

In addition to process development/further development during case hardening (carburizing and carbonitriding), the work of the working area includes the investigation of the process influence on the surface layer structure and the resulting component properties. The focus of the developments is also on the targeted adaptation of the surface layer structure to the respective specific loads by a targeted modification of the phase mixtures.

In industrial practice, martensitic surface layers with small proportions of retained austenite are usually produced during case hardening. The development of new surface layer structures of carburized and carbonitrided components by bainitic transformation or varying proportions of martensite, bainite and retained austenite with carbides and carbonitrides is being pursued as a central development trend for improved component properties.

 

 

Gas carburizing of helical gears

Induction hardening

Inductive surface hardening is an energy-efficient, environmentally friendly and fast technology for hardening the surface layer of components while maintaining the core strength of the quenched and tempered steels used. Due to tactile hardening and short heat treatment times, inductive heat treatment can also be flexibly integrated into the production chain. This allows optimized material flows to be achieved and throughput times and inventories to be reduced. In this process, heat is generated by means of Joule heat from eddy currents generated directly in the edge layer of the ferromagnetic material by means of electromagnetic induction, with current intensity in the inductor and frequency being the main parameters.

More recent developments allow the simultaneous application of different frequencies in order to adjust the energy input into the component in a targeted manner. The working area focuses on the process development with regard to the adaptation of the component properties to the respective requirement profile. The work contents are the consideration of the material dependence of corresponding heat treatments. Furthermore, the effect of the process parameters on the temperature field in the component is analysed. In addition, material and component properties resulting from a corresponding treatment are of interest. Moreover, possibilities of process modelling and simulation of the corresponding processes are considered. Investigations into contour hardening focus on the gear wheel as a component. The available dual-frequency technology offers the possibility to harden components (e.g. gears) close to the contour, i.e. similar to a case hardening layer.

 

 

Hardening of a rotating bending sample with a sharp notch during austenitizing of the notch area

Sensor technology and nitriding

Sensors enable automation in many areas of production with the associated improved quality assurance. In particular, the industrial transformation towards "Industry 4.0" requires further automation also in the various heat treatment processes. In the field of heat treatment, sensors are already successfully used in many areas, especially for temperature and atmosphere control. An important example is the use of oxygen and hydrogen probes in the carburizing and nitrocarburizing processes. With these sensors, reactive treatment atmospheres can be recorded, controlled and regulated. In carbonitriding, a sensor system with integrated simulation of the diffusion and precipitation processes has been successfully developed and brought to market in recent years.

The use of gas sensors is necessary but not sufficient, since they do not provide information about the current material condition, which is the main focus of interest as a target variable in heat treatment processes. Further work is therefore concentrated on the development of sensors to measure the current heat treatment condition. Successful developments such as the nitriding sensor for nitriding and nitrocarburizing processes, the development of sensors for the in situ qualification and quantification of the material microstructure such as bainite, martensite and tempering microstructure during heat treatment including adapted sequence controls could be realized in the past.

In the field of nitriding and nitrocarburizing processes, the focus is on process developments for stress-optimized component applications such as deep nitriding of gears and applications for hot and cold working tools as well as applications with narrow specifications in the steel spectrum from unalloyed to austenitic steels. In this context, facilities for the entire process and combination spectrum of nitriding and nitrocarburizing from plasma (incl. active lattice) and low pressure up to number-regulated normal pressure processes can be used.

In addition, we are also working on aspects of economy, sustainability and ecology such as the energy efficiency of nitriding plants and nitriding processes. Finally, basic topics such as pore formation or nitriding of non-ferrous materials such as aluminium, titanium and nickel alloys are also being pursued in close cooperation with industry. This also includes the further development of post-oxidation.

 

Plasma nitriding of a gear wheel

Simulation and Quenching Technology

The computational modelling of heat treatment processes opens up new possibilities for a heat treatment-compatible design. The focus is on the simulation of hardening processes and in particular of the quenching process, considering the influence of material inhomogeneities on the transformation behavior. According to the current state of the art, such work can only be designed with a basic orientation, since only a fraction of the influencing variables can be recorded and taken into account in the models. Furthermore, existing models are continuously being expanded with the aim of integrating process steps such as tempering into the simulation. Current topics in the modeling of heat treatment processes are bainitic transformation under stress, tempering and phase transformations in the additive production of hardenable steels.

Dimensional changes and distortion are a central problem in the production of components. They are often associated with heat treatment alone as one of the final manufacturing steps. In many cases, however, heat treatment steps only trigger plasticization due to thermally induced residual stress reduction, which is caused by previous manufacturing steps. Due to the extraordinary complexity of such processes, individual aspects have to be investigated and combined to form an overall picture on the basis of a long-term strategy. Currently, the heat treatment simulation deals with the influence of the component geometry on the dimensional and form changes, especially in the context of lightweight construction developments and the consideration of effects from previous processes (e.g. forming) with regard to the dimensional and form changes.

null

 

Calculation of deformation: Temporal development of the tilting of the gear rim and phase transformation during a quenching process in oil

The quenching technology focuses on the characterization of the quenching effect of oils and aqueous polymer solutions with regard to the target parameters microstructure and hardness. In addition, work in the field of gas quenching will continue. The further development of vacuum heat treatment systems in the field of high-pressure gas quenching has opened up new possibilities for replacing liquid with gaseous quenching media if the hardenability of the materials used is sufficient. The quenching effect is primarily determined by the parameters gas type, quenching pressure and inflow velocity. Investigations are under way to characterize the quenching effect in connection with vacuum heat treatments as well as following inert gas heat treatments. Besides aspects of distortion minimization, ecological aspects are in the foreground of the investigations.

[Translate to English:] Härterei

Projects of heat treatment

Development of a high-temperature heat storage system for storing waste heat from the post-combustion of exhaust gas of a nitriding furnace – NitroTES

Nitriding is a widely used but energy-intensive process in steel heat treatment. Thermal afterburning, used to mitigate NH3 emissions, generates waste heat up to 1000°C that currently remains largely unrecovered.

In collaboration with Leibniz-IWT Bremen, the startup Heatrix is developing a world-first recovery system: a 100 kWh high-temperature storage unit utilizing a solid-state ceramic structure to capture this heat for subsequent tempering processes.

Compared to conventional packed beds, this solid-structure design allows for optimized flow control and reduced pressure drops, enhancing overall efficiency. An electric air heater ensures thermal stability within the tempering furnace. This innovative power-to-heat approach significantly reduces reliance on fossil fuels and provides a scalable decarbonization strategy for industrial thermochemical processing

 

Cooperation: Leibniz-IWT PB I / Heatrix

Funding: BAB, Senatorin für Umwelt, Klimaschutz und Wissenschaft Freie Hansestadt Bremen

Schematische Darstellung des NitroTES-Wärmerückgewinnungssystems: Abgase (NH₃, H₂, N₂) aus einem Nitrierofen (Schachtofen, ~500 °C) werden in einer thermischen Nachverbrennung bei ~900 °C verbrannt. Das entstehende Heißgas wird über eine isolierte Leitung an einen keramischen Plattenwärmespeicher übertragen, der die Energie zwischenspeichert und als Warmluft (~400–600 °C) einem Anlassofen (Box Furnace) zum Anlassen von Zahnrädern und Wälzlagern zuführt. Nicht genutzte Abgase werden über einen Kamin abgeleitet.
Logo der BAB – Die Förderbank
Logo der Senatorin für Umwelt, Klima und Wissenschaft der Freien Hansestadt Bremen
Co-funded by the EU
Impact of machining-related surface layer changes on the nitriding response of forging tools

The thermochemical heat treatment nitriding is used to improve the surface properties of a workpiece by diffusing nitrogen 
into the surface layer to form precipitates. In tool manufacturing, these precipitates are used to increase the hardness 
and wear resistance of forging dies at elevated temperatures and thus their service life.
 

As no further finishing steps take place after nitriding, the tools are finished by grinding in their hardened or tempered state. During this hard finishing process, the workpiece surface layer is affected by the interaction of the material with the grinding tool and the metal working fluid as well as the thermomechanical load, which in turn affects the surface structure of the workpiece and thus the nitriding response. In this research project, the relationships between the design of the grinding process, the changes in the surface layer and the final nitriding treatment are investigated.


Cooperation: Leibniz-IWT WT/FT
Funding: BMWK-AiF/IGF (AWT)

Bild von sechs metallischen Probenstreifen des Stahls X38CrMoV5-3 mit unterschiedlicher Härte. Die drei linken Streifen sind mit „55 HRC“ gekennzeichnet, die drei rechten mit „41 HRC“. Die Oberflächen zeigen Unterschiede in Farbe und Struktur, wobei ein sichtbarer Verlauf auf unterschiedliche Oberflächenbehandlungen oder Verschleißtests hinweist. Hintergrund ist schwarz, Beschriftungen sind in Weiß gehalten.
WINDUCTION – Eco-design of an alternative production route for planet gears of wind turbine gearboxes

The main aim of the project WINDUCTION is the design of an eco-friendly and low-energy consuming production route for the planet gears of the wind turbine gearboxes.

Based on the replacement of carburizing by induction hardening, the following advantages are expected: reduction of CO2 emissions, avoiding the use of fossil fuel, and utilization of novel eco-friendly steels designed to improve their performance during the machining operations.

Funding: EU Project/RFCS-2020

 

Ein Diagramm zeigt den Verlauf von Eigenspannungen (in MPa) in Abhängigkeit vom Abstand zur Oberfläche (in µm) für verschiedene Stahllegierungen und Härtezustände. Die x-Achse reicht von 0 bis 5000 µm, die y-Achse von -800 bis +800 MPa. Sechs unterschiedlich farbige Kurven repräsentieren Kombinationen aus drei Stahlsorten (50CrMo4, 56NiCrMoV7, 56NiCrMoVBi7) jeweils im Zustand "Low Hardness" und "High Hardness". Zu Beginn (nahe der Oberfläche) liegen die Eigenspannungen meist im negativen Bereich und steigen mit zunehmender Tiefe in den positiven Bereich.
Use of carburizing processes free of internal oxidation and multi-stage phase transformation for high-strength surface layers

Case hardening is currently typical for highly stressed components such as gears. In contrast, isothermally transformed bainitic surface layers have hardly been investigated so far.

The combination of properties resulting from case hardening of a ductile core and a hard surface layer subjected to residual compressive stresses with a bainitic transformation offers the potential for a further increase in fatigue strength in the field of drive technology.


Cooperation: WZL Aachen
Funding: BMWK-AiF-IGF/AWT

Ein Wöhlerdiagramm (S-N-Diagramm) zeigt die Beziehung zwischen Lastwechsel (x-Achse, logarithmisch) und Spannungsamplitude in MPa (y-Achse) für verschiedene Werkstoffzustände oder Proben. Die Legende listet sechs Kurven auf: EH, 1B 210/16, 1B 250/7, 1B 210/8 T, 2B 210/8 190/16, 2B 210/8 230/16 und QPT. Die Spannungsamplitude nimmt mit zunehmenden Lastwechseln für alle Kurven ab.
FVA945I “Induction hardening of 3D printed gears” – Induction hardening of additively manufactured lightweight spur gears

The sustainable treatment of the environment as well as the efficient use of resources enable the preservation of our planet. Efficient and sustainable powertrains can be realized by gears with increased power density.

The combination of additive manufacturing and inductive heat treatment leads to the desired higher power density through increased strength and  reduced weight. Additive manufacturing using PBF-LB/M enables innovative and power-flow-compatible lightweight designs. Furthermore, the printed material has a high dislocation density, which can be utilized for higher surface hardness and increased component strength through efficient induction hardening. In the project, samples and gears of different materials, lightweight designs and heat treatments will be experimentally tested for their load-bearing capacity in order to determine mechanical parameters and thus identify the optimum combination with the greatest possible potential.
 

Cooperation: FZG TU-München
Funding: BMWK-AiF/IGF 20150 N/FVA 945 I

Metallisches Zahnrad mit Stützstruktur, gefertigt im 3D-Druckverfahren, auf einer runden Bauplattform.
Transregional CRC 136 “Process Signatures” – Transfer project T06: Data-based lifetime prediction for a function-oriented induction hardening process

The project aims to predict the process parameters of induction hardening in such a way that required 
component properties, such as the fatigue strength of shafts, are fulfilled in the context of function-orientated 
production. This is achieved by inverting the process signature and calculating local fatigue strengths.

Cooperation: eldec Induction GmbH
Funding: DFG (Transferbereich SFB TRR136)

Metallische Zugprobe in Knochenform mit schwarzer Markierung in Form eines „#“-Symbols und einer gebogenen Linie. Die Probe liegt auf einem grauen Hintergrund und wird vermutlich für mechanische Tests wie Zugversuche verwendet.
Influence of optimized low-temperature treatments on gear load capacity

Based on the results of previous research projects, further investigations are carried out to evaluate the 
effects of low-temperature treatments on the load-bearing capacity of case-hardened gears.

Cooperation: FZG
Funding: BMWK-AiF/IGF + FVA

Diagramm zeigt den Anteil an Restaustenit in Masse-% in Abhängigkeit von der Temperatur (in °C) zwischen -200 °C und +40 °C. Zwei Kurven mit orangefarbenen Datenpunkten stellen das Verhalten beim Kühlen und beim anschließenden Erwärmen dar. Der Restaustenit-Anteil steigt beim Kühlen deutlich an und bleibt beim Erwärmen zunächst konstant, bevor er wieder leicht sinkt. Eine senkrechte gestrichelte Linie markiert 0 °C.
Case-hardened shafts – Specific consideration of case hardening in the design of shaft-type components

Case hardening is a standard heat treatment in drive technology for the increase in fatigue strength of shaft-type 
components.

However, as was shown in a preliminary study, the existing calculation rules for shaft-type components 
(DIN 743, FKM guideline) are not capable of integrating the resulting surface layer conditions into a 
fatigue strength concept in a differentiated manner.

 

Cooperation: IMM Dresden, IKAT Chemnitz
Funding: BMWK-DLR-IGF/FVA

Darstellung einer FEM-Simulation (Finite-Elemente-Methode) eines wärmebehandelten Bauteils mit fünf farbcodierten Auswertungen: C-Gehalt (%), Härte (HV), Restaustenit (%), Temperaturverteilung und von-Mises-Spannung (MPa). Links ist ein schwarz-weißes Querschnittsbild des Bauteils. Die Ergebnisse zeigen graduelle Veränderungen entlang des Bauteils in Abhängigkeit von Tiefe und Geometrie. Farblegenden sind jeweils neben den Auswertungen abgebildet.
ICME-based alloy and process design towards fabrication of high-performance components with nano-bainitic structure

This project aims to set up an integrated simulation framework for the development of a case hardening steel and a 
case hardening process with optimized alloying elements and heat treatment parameters.

It is expected to generate an ultrafine nano-bainitic microstructure at the carburized surface which in turn 
significantly improves the fatigue performance of power transmission components. This is achieved by employing 
the ICME methodology and state-of-the-art experimental verifications as well as benchmarking the results with 
currently available commercial materials. The developed steel grade  and process are used for fabrication of power 
transmission components, initially in the automotive industry and later in the aerospace industry.
 

Cooperation: IEHK Aachen
Funding: FOSTA P1545

Schematische Darstellung eines Herstellungsprozesses für ein Bauteil mit ultrafeinem nanobainitischem Gefüge. Oben sind die einzelnen Prozessschritte dargestellt: von Legierungsdesign, Stranggießen, Schmieden, Glühen, spanender Bearbeitung, Aufkohlen, Abschrecken, Anlassen bis zur Hartbearbeitung. ICME-Punkte (Integrierte rechnergestützte Werkstoff- und Prozessentwicklung) sind markiert. Unten zeigt ein Querschnitt des Bauteils mit Vergrößerung das feine nanobainitische Gefüge mit Ferrit- (α) und Austenit-Phasen (γ).
Induction Hardening of Rolling Bearings – Influence of Process Parameters on WEA/WEC Susceptibility

White etching areas (WEA) and white etching cracks (WEC) have been identified as a significant link in the causal chain of premature rolling bearing damage.

The aim of this project is to develop an induction heat treatment method to prevent WEA/WEC damage in rolling bearings. Various rolling bearing specimens with both ring and disc geometries are being investigated to develop a comprehensive method. Initial preliminary tests with disc geometries have already been conducted in our hardening shop.

Cooperation: IWM Aachen University, MSE Aachen University

Funding: FVA

Der Versuchsaufbau für eine Scheibe, deren Oberseite durch einen darüber liegenden Ringinduktor erhitzt und anschließend abgeschreckt wird, um die Oberseite zu härten.
Increase of the strength of carbonitrided surface layers with high austenite content by thermal modification through tempering

Previous research projects have shown that carbonitrided gears with high-retained-austenite case layers and subsequent tempering at high tempering temperatures achieve sufficient hardness in the surface layer and high load-bearing capacities. The project therefore focuses on the scientific and technical relationships between carbonitriding in combination with high-temperature tempering, the resulting microstructure, and its properties in the component.

The dependence of hardness and retained austenite content on the temperature of the post-treatment was investigated on 18CrNiMo7-6 case-hardened steel in a carbonitrided state. After hardening, the basic state exhibits a retained austenite content of 56 % by mass with a surface hardness of approx. 64 HRC. Deep cooling increases the hardness due to the transformation of retained austenite into martensite. The tempering treatment also led to a transformation of the retained austenite content. At 250 °C, a residual austenite content of over 20 % by mass can still be determined. Furthermore, there is a tendency for the hardness to decrease continuously due to the relaxation of the martensite.
 

Cooperation: IWT-WT / FZG TU München

Funding: BMWE-DLR / IGF + FVA

 

Restaustenitgehalt und Härte in Abhängigkeit von der thermischen Nachbehandlung von 18CrNiMo7 6 im carbonitrierten Zustand
Investigation of the distortion behavior of nitrided wheels of bevel and hypoid gears

In previous FVA research projects, nitrided spur gears were found to have a higher tooth root and pit load capacity compared to the ISO standard. No investigation has yet been conducted into the transferability of nitriding with regard to distortion behavior and load-bearing capacity on bevel and hypoid gears. A feasibility study will therefore compare the distortion behavior of nitrided bevel wheels with that of case-hardened bevel wheels of the same geometry.

The change in the head cone angle deviation clearly illustrates the fundamental difference in the distortion behavior of bevel gears between the two heat treatment processes. As a result of case hardening, a characteristic tilting of the base body is observed due to the transformation processes during quenching. During nitriding, no phase transformations occur according to the time-temperature sequence, which means that no displacement of the base body are to be expected.

 

Cooperation: IWT-WT / FZG TU München

Funding: FVA

Änderung der Kopfkegelwinkelabweichung in Abhängigkeit vom Wärmebehandlungsverfahren
LowROx – Improved grindability of gears by reducing surface oxidation during gas carburizing

Gas carburizing followed by oil quenching is the most widely used case hardening process for gears. The presence of oxygen in the furnace atmosphere causes the formation of a non-martensitic transformation layer during gas carburizing due to surface oxidation. 

This relatively soft transformation layer has a highly detrimental effect on the gear grinding process following heat treatment, as the soft material causes the grinding wheel to clog more quickly and leads to weld deposits. For this reason, the LowROx project aims to investigate various strategies for reducing surface oxidation in order to increase the efficiency of grinding processes. These include, for example, changing the gas composition in the carburizing atmosphere. In addition, the use of a plasma injector should enable the use of pure hydrocarbons for the carburizing process.

 

Cooperation: IWT-WT / WZL RWTH Aachen

Funding: BMWE-DLR/IGF 

 

 

[Translate to English:] Auswirkungen der Randoxidation bei der Gasaufkohlung auf den Schleifprozess von Zahnrädern
N-Standards – Development of Calibration Standards for High Nitrogen Contents in Nitrided Steels

The project N-Standards addresses the limited comparability of nitrogen measurements in nitrided steels, caused by the lack of suitable calibration standards. The project aims to establish reliable and traceable calibration strategies for physico-chemical analysis methods, particularly glow discharge optical emission spectroscopy (GDOES).

In recent months, a chain-calibration approach combining certified steel standards, stoichiometric nitride coatings, and diffusion-based simulations was developed and validated. This enabled quantitative nitrogen depth profiling with reduced uncertainty (~10 %) and physically consistent results across the compound layer and diffusion zone. 

Further opportunities include developing reference materials with defined high nitrogen contents and extending the concept to additional nitride systems. The results support improved quality assurance in industrial heat treatment and surface engineering.

Cooperation: AWT, Robert Bosch GmbH, Prof. Hoffmann Werkstofftechnik, Härterei Carl Gommann GmbH

Funding: BMWK, funded via AiF / IG

[Translate to English:] Transformation von GDOES-Rohsignalen des Stickstoffs in quantitative Stickstoff-Tiefenprofile unter Anwendung einer RSF-basierten Kalibrierung und Unsicherheitsbewertung
NanoWinTur – Development of high-silicon-case-hardening steels

The NanoWinTur project is developing high-silicon case-hardening steels for use in wind turbine gearboxes. The high silicon content is intended to ensure the formation of carbide-free, nanostructured bainite in the surface layer during the carbo-austempering of gears, which is expected to result in superior strength properties. 

The transformation behavior of four test melts with up to 1.5 wt-% silicon was characterized in a dilatometer at different carbon contents. In addition, metallographic examinations and hardness tests were carried out. For the next step, samples were prepared for testing of the mechanical properties, carburized in a low-pressure vacuum furnace, and then transformed to bainite after re-austenitizing in a salt bath.

The most promising alloy will be selected for the subsequent production and testing of gears.

 

Cooperation: CENIM-CSIC, Sidenor, RWTH Aachen (WZL), ZF

Funding: EU-Project 101112398, RFCS-2022

 

[Translate to English:] REM-Aufnahmen des bainitischen Gefüges der vier Versuchsschmelzen bei 0,8 %C nach dem Bainitisieren bei 230 °C für 12h
Increased finite life fatigue strength of nitrided gear teeth

Previous research studies have shown that nitriding can be used to achieve high load-bearing capacity values in gears. However, nitrided gear teeth are sensitive to short-term overloads, which manifests itself in premature failures in the fatigue strength range. 

In practical applications, high safety factors must therefore be taken into account, meaning that the potential of the theoretically possible load-bearing capacities is not fully exploited. The project therefore aims to increase the fatigue strength of nitrided gear teeth through specific measures in the area of heat treatment.

A detailed analysis of the available results on the influence of the core structure on the nominal stress at the root of the tooth in the time-strength range revealed an optimum in the range of a core hardness of approximately 300 HV1. Accordingly, the blanks for the production of the test gears were treated at different tempering temperatures in order to achieve a comprehensive variation in core hardness.

 

Cooperation: IWT-WT / FZG TU München

Funding: BMWE-DLR / IGF + FVA

 

[Translate to English:] Variation der Härte nach dem Vergüten der drei eingesetzten Stähle
From primary forming to component recycling – digitised, circular production chains and energy analysis with DiStEL

The DiStEL project involves experimental and digital simulation of steel recycling using the example of an electric axle. To this end, steel melts at the IWT were deliberately ‘contaminated’ with copper and tin in order to simulate their enrichment in the electric steel route. The cast blocks are further processed by the cooperation partners and return later in the project as roller bearing rings and blanks for gear wheels. At the IWT, these were and are then analysed mechanically and metallographically.

Energy consumption was measured during the manufacturing steps so that individual CO2 loads could be assigned to the process as a whole as well as to the process steps and components and made traceable.

At the same time, the heat treatment ontology (HTO) is being developed to semantically map essential aspects of heat treatment. It thus contributes to the digitalisation of the steel production chain and is an application ontology of the Platform MaterialDigital Core Ontology (PMDco).

 

Cooperation: Leibniz-IWT PB I / PB II, Decoit / Bosch / Schaeffler / FIZ Karlsruhe / Fraunhofer IWM / ICAMS Bochum / IEHK Aachen

Funding: MaterialDigital3, FMRTS (Federal Ministry of Research, Technology and Space)

 

[Translate to English:] A Eingangsanalyse des Rohstahls, B Makroätzung des Gussblocks zur Analyse des Gussgefüges, C Wälzlagerinnenring mit Induktor in der Härteposition, D Hierarchie von Ontologien und Daten
Impact of machining-related surface layer changes on the nitriding response of forging tools

The thermochemical heat treatment nitriding is used to improve the surface properties of a workpiece by diffusing nitrogen into the surface layer to form precipitates. In tool manufacturing, these precipitates are used to increase the hardness and wear resistance of forging dies at elevated temperatures and thus their service life. 

As no further finishing steps take place after nitriding, the tools are finished by grinding in their hardened or tempered state. During this hard finishing process, the workpiece surface layer is affected by the interaction of the material with the grinding tool and the metal working fluid as well as the thermomechanical load, which in turn affects the surface structure of the workpiece and thus the nitriding response. In this research project, the relationships between the design of the grinding process, the changes in the surface layer and the final nitriding treatment are investigated.

Cooperation: Leibniz-IWT PB1 and PB3

Funding: BMWK / IGF-DLR-PT (AWT)

[Translate to English:] Schematische Darstellung des Projektes und seiner Ziele
„TIRIKA“ - Technologies and repair processes for sustainable aviation in the circular economy - Material development (metal)

In order to realize environmentally friendly aviation, increasing the degree of lightweight construction, using materials for new powertrain technologies and extending component service life are highly relevant. 

The aim is to develop a heat treatment process that enables the use of known lightweight alloys for hydrogen applications. Heat treatment and surface modification are to be used to optimize the strength of the existing lightweight alloys AlCr1.5Mo0.8Sc0.5Zr0.3 (ScanCromAl) and AlSi3.5Mg2.5 (Custalloy) and improve their hydrogen suitability. During precipitation hardening, different precipitation states will be set and it will be investigated which microstructure characteristics are robust against hydrogen embrittlement. In addition, it will be investigated whether a surface treatment, such as nitriding, has a positive effect on the mechanical properties of LPBF-produced components.

Cooperation: Airbus, Fraunhofer IFAM Bremen, Fraunhofer ILT Aachen

Funding: BMWK-LuFo

This image was generated using artificial intelligence.

[Translate to English:] Schematische Darstellung der Vorgehensweise zur Beladung von Proben aus dem PBF-LB/M mit H2 und Ergebnisse der Beladung
Turbo high-temperature steel: Increasing gearbox power density through high-temperature-resistant material systems for gears and roller bearings

Ensuring adequate cooling often represents a technical limitation in reducing the weight and size of gearboxes, especially in high-speed applications. Increasing speeds cause an increase in the heat energy generated by friction in the rolling contact, which cannot be adequately dissipated due to the reduced component and housing size and the poor accessibility of lubricant to the gear and bearing.

This leads to an increase in operating temperature. Heat dissipation is particularly challenging for functionally integrated gear components, such as planetary gears, as there are several heat sources in one component and they have separate requirement profiles (bearing + tooth engagement).

The aim of the research project is to use carbonitriding and bainitizing after case hardening conventional case-hardened steels (20MnCr5) to modify the surface layer structure so that it can withstand the increased operating temperatures due to its phase composition. Furthermore, alternative material concepts in a case-hardened and/or nitrided state are being tested, whose heat resistance is increased due to the alloy constellation (42NiSiCrMo8-7-3, M50NiL, and HybridSteel55). The tempering resistance of the states is being investigated by means of targeted aging at 210 °C (see Figure XX).

In addition to the development of customized heat treatments for the steels, a new test concept at elevated temperatures of up to 210 °C is being set up at the project partner WZL in Aachen to test the load-bearing capacity of the gears at operating temperature.

 

Caption: 20MnCr5, carbonitrided, oil-quenched and tempered (250 °C), microstructure after tempering

Cooperation: Leibniz-IWT PB1, WZL-Aachen

[Translate to English:] 20MnCr5, carbonitriert, ölabgeschreckt und angelassen (250 °C), Gefüge nach dem Anlassen
Ammonia wall reaction: Optimization of ammonia decomposition reactions during nitriding

The performance of components can be significantly improved by thermochemical coating in ammonia-containing atmospheres. The result depends largely on the proportion of unbroken ammonia, which is determined by thermal decomposition and catalytic reactions on components and furnace walls. Particularly in large furnaces, heterogeneous gas phase pyrolysis and low space velocities often lead to inhomogeneous treatment results.

The aim of the research project is to elucidate the ammonia decomposition reactions on different furnace wall materials and the resulting changes in the catalytic material boundary layer. Reaction kinetics and catalytic behavior are to be analyzed by means of laboratory investigations of gas phase pyrolysis and operational tests on long-term changes in the boundary layer.

Targeted furnace design and optimized operation increase the efficiency of heat treatment and sustainably reduce operating costs.

 

Cooperation: Leibniz-IWT PB I

Funding: FOGI, BMWK IGF / DLR-PT

[Translate to English:] Darstellung einer Graphit-Hartfilzprobe in der Thermowaage und abgeleitete Spaltergebnisse des Ammoniaks anhand des Wasserstoffgehalts der Atmosphäre