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Report No.

Microstructural development of multi-pass TIG welded F82H steels under dual-ion irradiation

Ogiwara, Hiroyuki; Tanigawa, Hiroyasu; Mizui, Tomohiro*; Kishimoto, Hirotatsu*; Koyama, Akira*

Reduced-activation ferritic/martensitic steels for first wall and blanket structural component applications in a fusion reactor required joining by welding, and effects of displacement damage and helium production on mechanical properties and microstructures are important to these applications. In the fabrication of blanket modules, the joints of a first wall/side walls will be applied to a multi-pass tungsten inert gas (TIG) welding. The objectives of this work are to clarify the helium effects on swelling behavior and the microstructural evolution in the region welded by a multi-pass TIG welding. F82H steels were irradiated at 470 $$^{circ}$$C up to high dose 20 dpa by using 6.4 MeV Fe$$^{3+}$$ and/or energy-degraded 1.0 MeV He$$^{+}$$. The damage rate is 3.0$$times$$10$$^{-4}$$ dpa/s, and the helium injection rate is 15$$times$$10$$^{-3}$$ appm He/s. Microstructure and Vickers hardness profiles across base metal, heat affected zone (HAZ) and fusion zone (FZ) were examined before irradiation experiments. The amount of hardness in FZ increased in increments of number in welding passes. The swelling resistance varied with the type considered due to the phase transformation that occur during the heating and cooling cycles of the fusion welding process. In dual-ion irradiated FZ, cavities were observed to a region from one pass to fourth passes and not fifth passes, and amount of swelling decreased in increments of number in welding passes. The tempered zone offered the largest amount of swelling across HAZ.



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