Comparative analysis of microstructure and creep properties in cast Inconel 625 welds fabricated by gas tungsten and shielded metal arc welding processes

This paper presents a comparative analysis of microstructural and high-temperature mechanical properties of Inconel 625 (IN 625) cast Ni-based superalloy welded using two different processes, i.e. gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW). For GTAW and SMAW processes, ERNiCrMo-3 and ENiCrMo-3 filler metals were employed, respectively. The base metal exhibited a gamma-matrix with a sparse distribution of the Laves phase, which was attributed to the microsegregation of Nb at the interdendritic region. After GTAW and SMAW, the fusion zone exhibited fine columnar grains resulting from rapid solidification. GTAWed and SMAWed IN 625 (G625 and S625, respectively) displayed the overmatched microhardness traverse. S625 exhibited slightly higher yield and tensile strengths than G625 at temperatures of 25, 650, 700, and 750 degrees C. Tensile fracture occurred at the Laves phase in the base metal, showing similar features in the two welds. However, the creep lives of G625 (8915-17044 h) were significantly longer than those of S625 (894-3125 h) at 700-750 degrees C, exhibiting different rupture behavior. After creep deformation, fracture occurred at the fusion line in G625, whereas in S625, the weld metal was fractured. In the crept weld metal of G625, although the Laves phase was slightly grown at the interdendritic regions, it rarely influenced creep rupture. Meanwhile, in the weld metal of S625, the Laves phase was noticeably grown despite the shorter creep time compared to that of G625. Higher contents of Fe and Si in the weld metal of S625 was responsible for the acceleration of the coarsening rate of the Laves phase, causing the short creep lives of S625 by acting as a crack initiation site. Accelerated cracking in the Laves phase can be evidenced by the low density of dislocations resulting from brittle fracture with minimal plastic deformation in the weld metal.