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@PHDTHESIS{Seehaus:979824,
author = {Seehaus, Mattis},
othercontributors = {Korte-Kerzel, Sandra and Springer, Hauke Joachim},
title = {{I}nvestigation of local chemistry, orientation
relationship and mechanical properties in martensitic
{F}e-{N}i-{C}-({S}i) steels},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-01868},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University; Dissertation, Rheinisch-Westfälische Technische
Hochschule Aachen, 2024, Kumulative Dissertation},
abstract = {In steels, martensitic phase transformation is one of the
best known transformations due to its contribution in the
development of the modern steel industry. It takes place
from a face-centred cubic high-temperature phase, austenite,
to a metastable body-centred cubiclow-temperature phase,
martensite. Especially in the industrial processing of
steels, the martensitic phase transformation is of crucial
importance, as it determines the strength of the material.
Despite numerous investigations, the detailed processes
during this phase transformation and the respective
orientation relationships between the phases are not yet
fully understood. In this work, the influence of silicon
(Si) on the carbon (C) redistribution in martensitic steels
at an ageing time of 2 years is investigated. One half of
each sample was quenched in liquid nitrogen in order to be
able to investigate the orientation relationship between
austenite and martensite after the martensitic
transformation. In comparison of the two alloys
$Fe-24wt\%Ni-0.4wt\%C$ and $Fe-24wt\%Ni-0.4wt\%C-2wt\%Si,$
the Si influence led to smaller initial austenite grains and
consequently smaller martensite lenses, but had no major
effect on the c/a ratio of the martensite lattice. The
results of the atom probetomography (APT) showed a different
segregation behaviour within the interface region between
austenite and martensite. In the alloy without silicon, iron
(Fe) enriched slightly in the martensite, while nickel (Ni)
and C depleted. This trend was not observed in the alloy
with Si, where only an increase of C and Ni and a sigmoidal
behaviour of silicon could be observed within the
interfacial region. Correlation with transmission electron
micrographs showed that carbon clusters formed along fine
{112}<111> twin boundaries in the martensite. The
determination of the predominant orientation relationship
between martensite and austenite was identified using
electron backscatter diffraction patterns. For this purpose,
a Matlab code based on the MTEX toolbox was developed, which
offers different modes of investigation. In transmission
electron microscopy, only single, individual orientation
relationships (ORs) can be analysed, whereas electron
backscatter diffraction (EBSD) images allow statistical
measurements on a large number of grains. In comparison of
the resulting pole figures (PFs) and on the basis of
theoretically generated PFs of ORs discovered in the
literature, the main OR could be identified as
Greninger-Troiano (GT) by means of an image comparison
algorithm as well as rotation angle deviation and
misorientation angle distribution. Furthermore, a two-step
optimisation process for the estimation of the single
crystal stiffness tensor from the indentation modulus is
presented, achieved by a correlative multiscale analysis
combining results based on first-principle calculations and
nanoindentation experiments with characterisation methods
such as SEM, EDS or EBSD. The possibilities and limitations
were investigated using pure austenitic FeNiC steel and a
multiphase Seymchan meteorite. It was shown that the
prediction of the anglular dependent elastic modulus is
possible on the basis of either directly DFT-simulated or
experimentally determined stiffness tensors, and that
different phase regions could be distinguished in a
correlated indentation modulus-hardness orientation plot.},
cin = {523110 / 520000},
ddc = {620},
cid = {$I:(DE-82)523110_20140620$ / $I:(DE-82)520000_20140620$},
pnm = {DFG project 406912286 - Atomare Umverteilung von
Kohlenstoff während der Austenit-Martensit-Umwandlung in
Stählen (406912286)},
pid = {G:(GEPRIS)406912286},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-01868},
url = {https://publications.rwth-aachen.de/record/979824},
}
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