The present study investigates the Microstructure, Microsegregation and Mechanical Properties of alloy 600 fabricated by Gas Tungsten Arc Welding technique with ERNiCrMo-10 filler wire. Optical and scanning electron microstructure was carried out to evaluate the microstructural changes in the fusion zone. EDS analysis was conducted to assess the microsegregation of alloying elements in the fusion zone. Strength and toughness of the weld joint were assessed by tensile and impact test. The results show that the presence of cellular structure in the fusion zone. EDS analysis revealed the Mo-rich M23C6 carbide phases in the interdendritic regions of the fusion zone. Strength and toughness of the weld joint improved 1 and 58% compared to the base metal strength and toughness. The presence of M23C6 improved the strength and toughness of the weld joint. © 2017 Elsevier Ltd.