This paper investigates the microstructural features and mechanical behavior of the dissimilar welded joint (DWJ) of lean duplex A 182 F 69 steel and 2.25Cr-1Mo (P22) steel. The multi-pass DWJ has been prepared using the Gas Tungsten Arc Welding (GTAW) process employing the Inconel 617 filler material. The DWJ has been subjected to post-weld heat treatment (PWHT) in a temperature range of 760 °C (PW 1)-810 °C (PW 2). The tensile testing and metallographic testing sample have been cross-sectioned from the DWJ for different heat treatment conditions of the welded joint. Each zone of the DWJ was characterized using the optical and scanning electron microscope (SEM). Cellular and columnar dendrites have been observed near the interface of weld fusion zone (WFZ) and heat-affected zone (HAZ) while equiaxed structure in center of the WFZ. The WFZ showed the austenitic structure with dendritic core and inter-dendritic boundaries. The inter-dendritic boundaries showed the presence of secondary phase particles, mainly enriched with Cr, Mo and Ti. Unmixed zone and compositional variation across the WFZ and HAZ interface have been observed on both the sides of DWJ. For as-welded condition, tensile fracture surface revealed the mixed mode of the fracture with tensile strength higher than that of the base P22 and F69 steel. The fracture location was in the center of the WFZ. For PW 1 condition, the crack initiation zone showed the mixed-mode while the final fracture showed the brittle fracture with cleavage facets. In PW 1, the fracture has been observed in HAZ of P22 side with strength lower than that of the base metal of F69. In PW 2 condition, complete brittle mode of the fracture has been observed and fracture surface showed the cleavage facets with river marking. © 2020 Elsevier B.V.