Microstructural characterization of 15Cr steel after quenching and slow cooling rates
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M. R. Ahmadi
Felix Meixner (1990) is studying Mechanical Engineering and Business Economics at Graz University of Technology. He has been working at the Institute of Materials Science since 2020 as a project assistant in the field of high temperature creep and materials for thermal energy power plants.
Abstract
Ferritic 15 %-Cr steels have better oxidation resistance, due to their higher chromium content, and creep strength, their lower dislocation density and lack of lath microstructure than conventional martensitic steels such as MarBN. Their mechanical properties are sensitive to chemical composition and heat treatment. In this study, we first simulated the formation of stable phases in two ferritic steels containing 2 % nickel (wt.%) and an alloy without nickel using the thermomechanical software MATCALC. Microstructural analysis using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) reveals the formation of carbides and intermetallic phases after diffusion annealing, both during rapid cooling in oil and slow cooling in the furnace. Dilatometry and XRD studies confirm the gradual phase transformation of ferrite to austenite from 650 °C onwards during heating. Dilatometry also shows that ferritic steels have a lower coefficient of thermal expansion than martensitic steels, austenitic steels, and superalloys, which results in lower thermal stresses during frequent start-up and shutdown of power plants.
Kurzfassung
Ferritische Stähle, die 15 % Cr enthalten, weisen im Vergleich zu konventionellen martensitischen Stählen, wie z. B. MarBN, aufgrund ihres höheren Chromgehalts, der höheren Kriechbeständigkeit, der geringeren Versetzungsdichte und dem Nichtvorhandensein einer lattenförmig ausgebildeten Mikrostruktur eine bessere Oxidationsbeständigkeit auf. Ihre mechanischen Eigenschaften reagieren empfindlich auf Änderungen in der chemischen Zusammensetzung und Wärmebehandlungen. Für die vorliegende Arbeit wurde zunächst mit Hilfe der thermomechanischen Software MATCALC die Bildung stabiler Phasen in zwei ferritischen Stählen simuliert, davon eine Legierung mit 2 % Nickel (Gew.-%) und eine Legierung ohne Nickel. Die Analyse der Mikrostruktur mittels Rasterelektronenmikroskopie (REM) und energiedispersiver Röntgenspektroskopie (EDX) belegt die Bildung von Karbiden und intermetallischen Phasen nach dem Diffusionsglühen, sowohl bei schneller Abkühlung in Öl als auch bei langsamer Abkühlung im Ofen. Mit Hilfe der Dilatometrie und XRD-Untersuchungen wurde die schrittweise Phasenumwandlung von Ferrit in Austenit ab einer Temperatur von 650 °C während der Aufheizung bestätigt. Die Dilatometrie zeigt zudem, dass ferritische Stähle einen niedrigeren Wärmeausdehnungskoeffizienten haben als martensitische Stähle, austenitische Stähle und Superlegierungen, was zu einer niedrigeren thermischen Belastung beim häufigen Anfahren und Abschalten von Kraftwerken führt.
About the author
Felix Meixner (1990) is studying Mechanical Engineering and Business Economics at Graz University of Technology. He has been working at the Institute of Materials Science since 2020 as a project assistant in the field of high temperature creep and materials for thermal energy power plants.
Danksagung
Die Autoren danken voestalpine BÖHLER Edelstahl GmbH & Co KG für die Herstellung der Legierungen und die maschinelle Fertigung der Proben, besonders Günter Zeiler und Rainer Fluch für die Koordination des Transports. Die Autoren bedanken sich ebenfalls bei Susanne Baumgartner und Jörg Steiner für deren wertvollen Input.
Die vorliegende Arbeit wurde im Rahmen des COMET-Programms im COMET K2-Zentrum für “Integrated Computational Material, Process and Product Engineering (IC-MPPE) (P2.4)”
Acknowledgements
The authors thank voestalpine BÖHLER Edelstahl GmbH & Co KG for producing the alloys and machining the samples, and especially Günter Zeiler and Rainer Fluch for coordinating their transportation. We also thank Susanne Baumgartner and Jörg Steiner for their valuable input.
The authors carried out this work as part of the COMET program within the COMET K2 Center “Integrated Computational Material, Process and Product Engineering (IC-MPPE) (P2.4)”
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Articles in the same Issue
- Meeting Diary
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- Microstructural characterization of 15Cr steel after quenching and slow cooling rates
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- Picture of the Month
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Articles in the same Issue
- Meeting Diary
- Frontmatter
- Editorial
- Editorial
- Microstructural characterization of 15Cr steel after quenching and slow cooling rates
- Corrosion behavior of Q345 steel in a simulated industrial atmosphere
- Failure Analysis
- Risk assessment of hitch pins connecting tractor and trailer to enhance the safety of humans using strain life fatigue approach
- Picture of the Month
- Picture of the Month
- News
- News
- Meeting Diary
- Meeting Diary
