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@PHDTHESIS{Akyel:1024586,
author = {Akyel, Fatma Nur},
othercontributors = {Reisgen, Uwe and Kannengießer, Thomas},
title = {{R}eduktion von {E}igenspannung und {V}erzug beim
{L}aserstrahlschweißen von nichtrostendem {S}tahl und
{B}austahl durch den {LTT}-{E}ffekt},
volume = {2026,1},
school = {Rheinisch-Westfälische Technische Hochschule Aachen},
type = {Dissertation},
address = {Düren},
publisher = {Shaker Verlag},
reportid = {RWTH-2026-00167},
isbn = {978-8191-0465-7},
series = {Aachener Berichte Fügetechnik},
pages = {1 Online-Ressource : Illustrationen},
year = {2026},
note = {Druckausgabe: 2026. - Auch veröffentlicht auf dem
Publikationsserver der RWTH Aachen University; Dissertation,
Rheinisch-Westfälische Technische Hochschule Aachen, 2025},
abstract = {This work investigates the low transformation temperature
effect (LTT-effect) in ferritic-pearlitic mild steel and
austenitic CrNi steel during laser beam welding. In contrast
to what is common in the literature, no special filler
materials are used; instead, the chemical composition in the
weld seam is generated in situ using dissimilar combinations
of conventional materials. The aim is to influence the
martensite transformation temperature and strain behaviour
by varying the material composition in the weld seam.
Chemical analyses, metallographic examinations and hardness
measurements are carried out in laboratory tests in order to
analyse the changes in microstructure and the dependence of
hardness on the martensite transformation temperature. The
results are compared with reference welds (similar welds).
Residual stress measurements show that residual compressive
stresses occur in LTT-welds, while tensile residual stresses
dominate in reference welds. The level of residual
compressive stresses depends on the chemical composition.
These results are supported by diffraction experiments. In
order to understand the strain behaviour during the phase
transformations, experiments are carried out on selected
CrNi steel samples at the Deutsches Elektronen-Synchrotron
(DESY). It is shown that martensite formation continuously
builds up compressive stresses that compensate for thermal
shrinkage. Thermal simulations determine the transformation
temperature and the time at which the compressive stress is
introduced. By calculating the strains, the compressive
strain behaviour due to the LTT effect can be highlighted.
Displacement transducer measurements confirm that the LTT
effect reduces component distortion. In summary, it is shown
that the LTT effect can be successfully used with dissimilar
material combinations in mild steel and CrNi steel in order
to generate specific compressive stresses and minimise
distortion. In particular, depending on the load case, the
required compressive strain can be adjusted by varying the
chemical composition.},
cin = {417610},
ddc = {620},
cid = {$I:(DE-82)417610_20140620$},
pnm = {SFB 1120 A07 - Nutzung der partiellen metallurgischen
Injektion zur Steuerung der Erstarrungskräfte bei
Schmelzschweißprozessen (A07) (260044599) / SFB 1120:
Bauteilpräzision durch Beherrschung von Schmelze und
Erstarrung in Produktionsprozessen},
pid = {G:(GEPRIS)260044599 / G:(GEPRIS)236616214},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
doi = {10.18154/RWTH-2026-00167},
url = {https://publications.rwth-aachen.de/record/1024586},
}
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