Influence of post-weld heat treatment in buttered interface of AISI 4130 and Inconel alloy welded joints

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. However, the true effectiveness of this procedure 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 post-weld heat treatment on the mechanical and microstructural behavior of the buttered dissimilar interface of AISI 4130 steel with nickel alloys. Gas metal arc welding processes in continuous and pulsed current modes were employed. AWS ERNiCrMo-3 (Inconel 625) and AWS ERNiCrMo-15 (Inconel 725) solid wires were used as filler metals. Post-weld heat treatment was performed on the buttered plates. The microstructure at the interface of the buttered fusion line were characterized by optical microscopy and scanning electron microscopy. Microhardness analyses were performed at the interface of the buttered weld. The results showed that gas metal arc welding process with pulsed current mode and Inconel 625 as filler metal showed lower levels of dilution and greater control of the partially diluted zones, proving to be more suitable for this type of application. It was also found that regardless of the welding procedure, post-weld heat treatment made the interface more brittle.