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ICFRM-12 Santa
Barbara, 4-9 December 2005
Abstract
Assessment of different welding techniques for joining EUROFER blanket components
Michael Rieth
Forschungszentrum
Karlsruhe, Institut für Materialforschung I, Karlsruhe, Germany
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 partially from softening in the vicinity
of the heat affecting zones. With respect to specific Test Blanket Module
design and assembly requirements for DEMO there might be a significant discrepancy
between necessary post-welding heat treatments and their applicability.
Therefore,
tungsten-inert-gas welds with EUROFER filler wire, electron beam, and laser
welding were used to join EUROFER plates. Specimens were fabricated for a
comprising qualification of their mechanical properties by tensile, charpy, and
creep tests. The focus was laid on the study of post weld heat treatments at
lowest possible temperatures and for maximum recovery of the joints at the same
time. All mechanical tests were accompanied by microstructure examinations.
The
lowest reasonable post-welding heat treatment for EUROFER was tempering at
700 °C. All tensile and creep specimens fractured outside the welding
zones and showed slightly increased strength. But significant differences in
impact bending properties could be determined. Both, electron beam and laser
welded joints showed ductile-to-brittle transition behaviours nearly as good as
the base material while tungsten-inert-gas welds remained rather brittle which
necessitated two-step heat treatments including annealing at or above the
austenitization temperature. This result clearly favours beam welding
techniques for components were high post-welding heat treatment temperatures
are inapplicable. On the other hand, unavoidable material flow necessitates
beam stoppers which, in turn, restrict their appliance.
Corresponding Author: Dr.
Michael Rieth
Forschungszentrum
Karlsruhe, IMF-I
Hermann-von-Helmholtz-Platz
1
76344
Eggenstein-Leopoldshafen, Germany
P.O.
Box 3640, 76021 Karlsruhe, Germany
Tel. +49 7247 82
2909, Fax +49 7247 82 4567
michael.rieth@imf.fzk.de