The formation of brittle microstructures around the fusion line in dissimilar welds has required a deeper microstructural analysis in this region. The study becomes more relevant when these welds are used in environments that facilitate hydrogen embrittlement. The present work aims to characterize the microstructure and hardness at the diluted zone interface in joints welded with dissimilar materials. Aiming for a better efficacy in the microstructural characterization of this zone, samples of both normal cross-section (NCS) and section with slope were used, according to the low-angle microsectioning (LAMS) technique, which allows a greater amplification of partially mixed zones (PMZs). The results indicated the diffusion of carbon from the heat-affected zone (HAZ) towards the fusion line which, in combination with other alloying elements, form highly brittle carbides. In turn, the hardness of the base metal and the HAZ was reduced after post weld heat treatment, whereas in the weld metal an opposite behavior was observed. The dissimilar interface was promising for applications in environments facilitating hydrogen embrittlement, especially regarding the characteristics of zone Φ.

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Dissimilar joints are often used by the oil and gas industry to join components such as forged flanges and piping used in subsea operations. The technique consists of buttering the forged flange before the closure weld is made. After the buttering runs, the forged flange is subjected to a post weld heat treatment (PWHT). However, the true effectiveness of PWHT has been questioned after failures began to occur in the fusion zone of the forging piece and nickel alloy. The present work aims to investigate the influence of PWHT on the mechanical and microstructural behavior of the buttered dissimilar interface of AISI 4130 steel with nickel alloys. GMAW-P and GMAW-C welding processes with AWS ERNiCrMo-3 (Inconel 625) and AWS ERNiCrMo-15 (Inconel 725) filler metals and the application of PWHT were used. The microstructure at the interface of the buttered fusion line were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). Microhardness analyses were performed at the interface of the buttered weld. The results showed that the welding procedure is critical for controlling the partially diluted zones (PDZs) at the buttered weld interface. It was also found that regardless of the welding procedure, PWHT made the interface more brittle.

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