In the present research, different weld layers were deposited on a 1.2714 steel die by gas tungsten arc (GTA) welding with the weld wire of Udimet 520, and effects of welding parameters on microstructure and mechanical properties of Udimet 520 superalloy were investigated. The results showed Udimet 520 weld with cellular–dendritic and rarely dendritic structure including c matrix rich of Cr, Mo and W, low percentage associated with order morphology and relative uniform distribution of MC type carbides. Udimet 520 alloy showed high resistance against hot cracking during welding and hot cracking occurred only at high input heat values. Also, cracking during welding occurred at the places that the concentration of Al and Ti is high. Investigation of the effect of welding parameters on the hardness of GTA welded Udimet 520 showed that with increasing welding speed and decreasing input heat, the hardness of the weld improved. Increase in hardness of GTA welded Udimet 520 due to increasing welding rate and decreasing heat input is attributed to the fineness of columnar structure and solid solution strengthening.
