Influence of post-weld heat treatment on the microstructure and hardness of dissimilar buttered and welded joints with nickel alloys

Abstract 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.