Optimization of laves phase strengthened high performance ferritic stainless steels

Fan, Xiuru; Krupp, Ulrich; Schwaiger, Ruth

doi:HT020482063

Optimization of laves phase strengthened high performance ferritic stainless steels = Optimierung mittels Laves-Phase verfestigter ferritischer Hochleistungsstähle

Fan, Xiuru^RWTH*

2020

Verantwortlichkeitsangabevorgelegt von Frau Xiuru Fan, Master of Engineering

ImpressumAachen 2020

Umfang1 Online-Ressource (IX, 143 Seiten) : Illustrationen, Diagramme

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Veröffentlicht auf dem Publikationsserver der RWTH Aachen University

Genehmigende Fakultät
Fak05

Hauptberichter/Gutachter
Schwaiger, Ruth (Thesis advisor) ; Krupp, Ulrich (Thesis advisor)^RWTH*

Tag der mündlichen Prüfung/Habilitation
2020-05-27

Online
DOI: 10.18154/RWTH-2020-06177
URL: https://publications.rwth-aachen.de/record/792517/files/792517.pdf

Einrichtungen

Inhaltliche Beschreibung (Schlagwörter)
creep (frei) ; ferritic stainless steel (frei) ; high temperature steel (frei) ; lavesphase (frei) ; thermomechanical processing (frei)

Thematische Einordnung (Klassifikation)
DDC: 620

Kurzfassung
This research aims at the development and optimization of High Performance Fully Ferritic (HiperFer) stainless steel. HiperFer steels were designed for the application in the next generation of ultra-supercritical thermal power conversion systems, with the steam working atmosphere at high temperature. Optimization of the newly designed HiperFer alloys via chemical composition adjustment and thermal / thermomechanical processing was investigated， and potential practical applications of HiperFer alloy were discussed. Microstructure and mechanical properties of HiperFer steels are highly influenced by alloying composition and thermal / thermomechanical treatment. In addition, the thermomechanical treatment window of HiperFer alloys is influenced by the chemical composition. Thermomechanical treatment including thermal and combined thermal - mechanical treatment is an advanced approach to optimize the properties of this type of steels. Recrystallization, precipitation treatment and mechanical deformation during the forming process highly influence the microstructure of HiperFer and thus the resulting mechanical properties. The interrelations between chemical composition and the resulting thermomechanical treatment windows are complex. For this reason, particle nucleation and growth, size and density of particles, as well as the influence of different chemical compositions on the thermomechanical treatment window were investigated. To widen the scope of potential practical applications of HiperFer, further adjustments of chemical composition were implemented. The impact of changes in thermomechanical treatment parameters on microstructure and mechanical properties was investigated in detail, by thermomechanical treatment simulation in laboratory scale and accompanying microstructure characterization on various length scales. This provided a systemic view of the impact of different treatment parameters on microstructure evolution and mechanical properties. Furthermore, the impact of alloying elements in interrelation with processing parameters was analyzed, and finally the influence of chemical composition on the resulting thermomechanical processing window was investigated. The results contribute to optimization of the HiperFer steels in various instances: First, modified alloying compositions have been derived to increase mechanical strength, which provide a broader range of potential applications; Second, process parameters can now be estimated based on the chemical composition, which saves a large amount of experimental work and supports the transfer to industrial processing; Third, combining thermodynamics and processing recursive optimization of both composition and processing according to desired mechanical properties will become possible by implementing the experimental data from this research into modelling tools.

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