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EUROMAT 2005 Prague,
5-9 September 2005
Abstract
Microstructure
and Mechanical Properties of Different EUROFER Welds
M. Rieth
Forschungszentrum
Karlsruhe, Institut für Materialforschung I, P.O. Box 3640, 76021 Karlsruhe
In contrast to austenitic
steels untreated welded joints of ferritic-martensitic steels like EUROFER
suffer from hardening and embrittlement due to uncontrolled martensite
formation in the weld and from softening in the vicinity of the heat affecting
zones. With respect to specific Test Blanket Module (TBM) design and assembly requirements
for DEMO there is a significant discrepancy between the necessary post welding
heat treatment and its applicability. Therefore, Tungsten-Inert-Gas (TIG) with
EUROFER filler wire, Electron Beam (EB), and Laser welding have been applied to
EUROFER plates in the condition as received. Prior
to specimen fabrication the microstructure of the different welds have been
investigated. Both TIG welds show coarse grain formation which is typical for
solidification micro structures that form during the welding cycles. Both beam
welds don’t show this severe grain coarsening. Also typical for TIG welds are
the softened regions in the HAZ as can be seen from the hardness profiles.
While the lateral extensions of the beam welds are significantly smaller,
softening in the HAZ cannot be observed here. From these microstructural
examinations it is already clear that TIG welds need a full two-step heat treatment
(austenitization plus annealing) in order to recover a uniform distributed fine
grain. This was also confirmed by poor charpy test results. But charpy tests on
beam welded specimens have shown surprisingly good results, even without
post-weld heat treatment. Compared to the EUROFER base material, the
Ductile-to-Brittle-Transition-Temperature (DBTT) of Laser and EB welds is almost
comparable. Further assets and drawbacks of these different welding
technologies are discussed in detail based on tensile and charpy tests
performed on welds with and without applied post-welding heat treatments. The
examinations were completed by according microstructural examinations.
280 words