Effects of W Content on the Microstructure and Mechanical Properties in TIG Welded Joint of Reduced-Activation Ferritic/Martensitic Steels for Fusion Reactor

In this study, the effect of W content on the microstructure and impact property in TIG welded joint of reduced- activation ferritic/martensitic (RAFM) steels was investigated. For this purpose, two types of RAFM steels with different W contents and filler wires of the same composition were prepared. After TIG welding, a post-weld heat treatment (PWHT) was performed at 730 ℃ for 1 h. Microstructures of the weld metals were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The weld metal with low W content (1.2 wt.%) consisted of tempered martensite and precipitates of intergranular M23C6 and fine MX within the laths. An increase in W content caused the formation of δ-ferrite and the coarsening of M23C6 carbide. Mechanical properties of the weld metals were evaluated by Vickers hardness and Charpy V-notch impact tests, indicating that the impact properties of the weld metal decreased significantly with an increase in W content. Finally, the relationship between microstructure and mechanical properties in the weld metal was discussed.