Weldability of a novel FeCrAl alloy : Investigation on Microstructure, Crack susceptibility and Transition Temperature

This master thesis investigates the weldability of Vesca, a novel titanium-alloyed FeCrAl fillermetal, compared to Kanthal® A-1 and Kanthal® AF fillers, for welding Kanthal® APM (aferritic FeCrAl alloy) and dissimilar joints with Alleima® 353MA (an austenitic stainless steel). The study aims to lower the ductile-to-brittle transition temperature (DBTT), enhancetoughness, minimize aluminium nitride (AlN) formation in dissimilar welding, and reduce preheating/post-weld heat treatment requirements. Using Tungsten Inert Gas (TIG) welding, the research evaluates Bead on Tube, overlay, and butt welds through microstructural analysis (LOM, SEM, EBSD) and Charpy impact testing. Vesca successfully eliminated AlN formation in dissimilar welds by promoting stable titanium nitride (TiN) precipitates, enhancing corrosion resistance. However, it exhibited coarser grains (387.46 μm, ASTM 0.80) in Bead on Tube welds on Kanthal® APM and a higher DBTT (~295°C) with lower toughness(45.54 J at 400°C) compared to Kanthal® A-1 (~210°C, 66.11 J) and Kanthal® AF(~260°C, 66.33 J) in similar butt welds, attributed to complex precipitates (e.g., Al₂O₃, metalcarbo-nitrides). In dissimilar butt welds, Vesca achieved significant grain refinement (~68%smaller than Kanthal® A-1), particularly near Alleima® 353MA, due to nitrogen-enhancedTiN nucleation. Challenges included poor flowability and porosity in Vesca butt welds, likely due to slag inclusions and unoptimized parameters. The study highlights Vesca’s potential for dissimilar welding but suggests further optimization for similar welds, recommending comprehensive mechanical testing, and advanced precipitate characterization to enhance its performance in high-temperature industrial applications.