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@PHDTHESIS{Ppperlov:835136,
author = {Pöpperlová, Jana},
othercontributors = {Bleck, Wolfgang and Singheiser, Lorenz and Krupp, Ulrich},
title = {{V}erformungsinduzierte {A}usscheidung intermetallischer
{L}aves-{P}hase in hochwarmfesten ferritischen {S}tählen},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2021-10328},
pages = {1 Online-Ressource : Illustrationen, Diagramme},
year = {2021},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2022; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2021},
abstract = {Single-phase, Laves phase strengthened, ferritic steels
with a chromium content of 17 $wt-\%$ potentially show
sufficient oxidation and creep resistance at high
temperatures. Alloying with tungsten, niobium and silicon
enables reaching the desired combination of high oxidation
resistance and creep strength by solid solution and
precipitation strengthening effects. These alloying elements
enhance the formation of the strengthening intermetallic
(Fe,Si,Cr)2(W,Nb) Laves phase particles, finely dispersed in
the matrix. The attainable oxidation and creep resistance
open up numerous high-temperature application fields, such
as steam transfer components in steam power plants or
thermal energy conversion and storage systems. This
dissertation deals with the optimisation of the chemical
composition as well as with the development of an innovative
thermomechanical manufacturing process of these
high-chromium stainless steels, which is considerably more
economical compared the conventional, solely thermal
processing. The further alloy design of this steel was
accomplished by thermodynamic modelling (ThermoCalc®) and
the results of preliminary research and development of
HiperFer (High Performance Ferritic) steels at the Steel
Institute at RWTH Aachen University (IEHK) and at the
Institute of Energy and Climate research (IEK) at Jülich
Research Centre. The main task of the alloy optimisation was
to minimise the undesirable brittle σ-phase and to maximise
the phase amount of the strengthening Laves phase. Within
the development of the thermomechanical manufacturing
process, the impact of the forging parameters on the
precipitation behaviour of the Laves phase was investigated
by hot forging experiments on a laboratory scale. The
precipitation states achieved were analysed and evaluated by
microstructure characterisation utilizing scanning electron
microscopy (SEM) and particle analysis using the ImageJ and
analySISPro® software tools. The mechanical properties
obtained were correlated with the chemical composition, the
applied deformation parameters and the observed
precipitation. The desired thermomechanically induced,
finely dispersed Laves phase precipitation was achieved on a
laboratory scale with a sufficiently strengthening effect
compared to the conventional thermal manufacturing process.
Based on these results, an up-scaling forging trial on an
industrial scale was successfully provided. However, further
optimisation of the process parameters remains to be
undertaken. Since two alloys with a varied tungsten content
were designed and produced within the scope of this
dissertation, the impact of tungsten, the main Laves phase
former, on the precipitation behaviour of the Laves phase
and on the final strengthening effect were examined.},
cin = {522110 / 520000},
ddc = {620},
cid = {$I:(DE-82)522110_20140620$ / $I:(DE-82)520000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2021-10328},
url = {https://publications.rwth-aachen.de/record/835136},
}
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