Fachzeitschrift ÖGS 05/06/2019

input during the process was restricted by fast responsive
current and voltage pulses that allowed a synchronized
arcing and short circuiting at a low arc power. The effect of
heat input and thermophysical properties of base materials
on the bead profile, joint strength, and distortion was studied
extensively. The results indicated a rational improvement
of joint quality with lowering of the heat input within
a restrictive range of processing conditions such as wire
feed rate and travel speed. Most importantly, the mixedmetal
assembly exhibited different thermal distortions with
the aluminum top sheet undergoing greater distortion than
the bottom steel sheet due to a higher coefficient of thermal
expansion.
Improving the integrity and the microstructural
features of electron beam welds of a creep-resistant
martensitic steel by local (de-)alloying
• A. Rabl, F. Pixner, B. Duarte, D. Blatesic, C. Béal,
N. Enzinger
Martensitic 9–12% chromium steels present the most preferred
material group for high-temperature components in
thermal power plants. Previous investigations revealed that
due to the use of a creep-resistant martensitic steel
strengthened with boron and nitrogen (MarBN), the minimum
creep rate can significantly be decreased. Furthermore,
the formation of the fine-grained heat-affected zone
(FGHAZ) due to welding can be suppressed. This FGHAZ is
subject to the most dominant failure mode (type IV craccing)
of welded joints during creep exposure. By using electron
beam welding, the total width of the heat-affected
zone (HAZ) can be reduced compared to conventional arc
welding processes. Preceding investigation on electron
beam welding of MarBN steel showed recurring difficulties
with hot craccing within the fusion zone. Various approaches
were tried to produce defect-free welds without the
use of any filler metal, but no satisfactory results were
achieved. In this investigation, the chemical composition of
the fusion zone was modified by the addition of conventional
9% chromium creep-resistant steel as a filler material.
By using the filler material, the fusion zone was locally
(de-)alloyed and defect-free joints of MarBN steel were
produced.
A new constitution diagram for dissimilar metal welds
of high-manganese steels
• B. Wittig, M. Zince, S. Jüttner, D. Keil
When dissimilar metal welding of high-manganese (Fe-Mn)
steels with low-alloyed steels, martensite may form in the
weld metal. Current constitution diagrams for weld metal
microstructure prediction cannot be used for Fe-Mn steels
since the influence of the high manganese content in those
steels is not sufficiently considered in the Ni equivalent.
This paper concentrates on the development of a new constitution
diagram for reliable weld metal microstructure
prediction when dissimilar metal welding of Fe-Mn steels
with low-alloyed ferritic and martensitic steel grades. For
developing the constitution diagram a specially designed
arc melting technique was used to experimentally simulate
dissimilar weld metals in different dilutions and compositions.
The resulting samples were evaluated regarding the
type and quantity of the microstructural phases by means
of hardness and ferrite number measurements as well as
light-optical microscopy. Using this dataset it was possible
to determine functional correlations between the chemical
composition and the weld metal microstructures. By means
of statistical analysis, a new constitution diagram was developed.
Actual GMAW welds of different material combinations
were performed to validate the applicability of the
diagram. The new constitution diagram has a very high prediction
accuracy and also distinguishes between the different
types of martensite (ε and α’).
Application of self-piercing nuts during hot forming of
22MNB5
• S. Meyer, G. Meschut, H. Vogt, B.-A. Behrens, S.Hübner,
A. Neumann
The increasing use of hot-formed steels for structural components
in lightweight construction requires solutions to
create mounting points into the thin blanc of high-strength
steel. Compared to welding nuts, self-piercing nuts are often
used due to advantages for the mechanical properties.
The problems of setting these elements in hot-formed
steels lice 22MnB5 are high process forces and often limited
undercuts, which are produced during the joining process.
In this regard, the application of the self-piercing nut
during the hot forming process of 22MnB5 is the focus of
the investigation. The particular challenge is to find out the
desired process parameter in a defined temperature window.
Thus, the ductile austenitized 22MnB5 is exploited,
while the local shape of the deformed blanc in contact with
the self-piercing nut is realized. A newly developed process
enables insertion of the self-piercing nuts by different
joining conditions. In order to evaluate the efficiency of the
new process, various aspects are recorded. To achieve a
successful hot forming process by a complete martensitic
microstructure transformation, a minimum cooling rate of
27 K/s is provided. Furthermore, it has to be assured, that
there is no thermal influence on the nut element, while the
blanc and the self-piercing nut are strongly heated. Otherwise,
this can lead to a change in the strength class of the
nut. For this purpose, hardness measurement is used to
analyze the microstructure development. The mechanical
behavior is described by torsion- and pull-out tests.
SCHWEISS- und PRÜFTECHNIK 05-06/2019 101