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@PHDTHESIS{Chang:837911,
author = {Chang, Yuling},
othercontributors = {Bleck, Wolfgang and Mayer, Joachim},
title = {{E}vidence and effects of heterogeneities in complex phase
and dual phase steels},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2022-00172},
pages = {1 Online-Ressource : Illustrationen},
year = {2021},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2022; Dissertation, Rheinisch-Westfälische
Technische Hochschule Aachen, 2021},
abstract = {Heterogeneous materials are extensively used in daily life.
As a typical example of heterogeneous materials, advanced
high-strength steels (AHSS) normally consist of various
constituents with distinct properties to achieve enhanced
combination of strength and ductility. However, a
comprehensive description of heterogeneities in AHSS is
currently absent. In this study, the correlation among the
compositional, microstructural and property heterogeneities
is explored by employing four commercial grade dual-phase
(DP) and complex-phase (CP) steels. A correlative
characterization approach combining various electron
microscopic techniques and nanoindentation is developed and
utilized to characterize these heterogeneities. Based on the
results, Mn is alternately enriched and depleted in bands
parallel to the rolling direction, while the local C content
is closely associated with the spatial phase distribution.
The comparison between DP800 and CP800, which were
fabricated from the same cast but differently heat treated
in the intercritical annealing regime indicates Mn
segregation impacts the phase transformation and C
distribution throughout the whole manufacturing process. In
DP800, the heterogeneity of C distribution was more
pronounced and martensite inherited from the Mn banding due
to the lower intercritical annealing temperature, which led
to the smaller fraction of austenite and intensive C
partitioning. On the other hand, CP800, heat treated at
higher intercritical annealing temperature, exhibited a more
homogenous C distribution and resulted in a more homogenous
distribution of martensite. The Mn segregation bands and
their impact on martensite morphology and location is
reflected by the local hardness distribution. In addition to
their varying partitioning in present phases, C and Mn
distribute heterogeneously in some individual grains/area,
which cause variation in local properties. The hardness
distributions of investigated materials were characterized
through nanoindentation. The results indicate the
conventional hardness difference between phases is not
applicable to correlate the heterogeneous microstructure
with the stretch-flangeability of the material. Therefore, a
new approach combining the Shannon entropy of hardness
distribution and spread of local hardness with respect to
microstructure is developed, which successfully links the
microstructure and hardness heterogeneity with material’s
local formability. The present work deepens and expands the
current understanding and knowledge of the heterogeneous
microstructure and hopefully the derived conclusions provide
guideline for future material design by fabricating the
heterogeneities of microstructure to achieve desired
properties.},
cin = {522110 / 520000},
ddc = {620},
cid = {$I:(DE-82)522110_20180901$ / $I:(DE-82)520000_20140620$},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-00172},
url = {https://publications.rwth-aachen.de/record/837911},
}
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