Welding technology development for the fabrication of vacuum vessel for CFETR

The vacuum vessel (VV) is an important component in the Chinese Fusion Engineering Test Reactor (CFETR). Various welding methods have been applied in manufacturing of the VV. The electron beam welding (EBW) technique was applied in the fabrication of the port stubs of VV taking advantages of low welding deformation and capable of manufacturing full penetration welds of complex geometry with heavy thickness by a single pass. While narrow gap tungsten inert gas (NG-TIG) welding featuring wide application scope and high welding quality have been applied in the welding of 1/32 V V. Microstructure and mechanical properties of EB welded and NG-TIG welded 50-mm-thick 316 L are investigated. The EBW weld microstructure characterized by columnar and equiaxed ferrite in austenite while NG-TIG weld consisted of typical single austenite phase and a little δ-ferrite. Different solidification behaviour lead to different microstructures. Tensile tests, in line with microhardness results, demonstrated that higher strength in NG-TIG weld than base metal (BM). However, the impact absorbed energy in both EB and NG-TIG welded joints were lower than the BM. Besides, both welds exhibited excellent bending properties.