Effects of GTAW process and post-welding heat treatment on the microstructure evolution, cracking behavior and hardness of Inconel 939 superalloy using Inconel 617 filler metal

This study investigates repair welding of service-aged Inconel 939 superalloy (100,000 operational hours) using gas tungsten arc welding (GTAW) with Inconel 617 filler metal. The research focuses on three key challenges: (1) irregularities in pre-existing MC carbides, (2) heat-affected zone (HAZ) liquation cracking, and (3) post-weld heat treatment (PWHT) effects on microstructure evolution and hardness distribution. Initial welding revealed a 91 μm HAZ crack, identified as liquation cracking caused by localized melting of service-induced lamellar carbides along grain boundaries. PWHT yielded microstructural improvements and hardness homogenization across the weld pool, partial melting zone (PMZ), and HAZ. However, the heat treatment also promoted crack growth to 386 μm, characterized as strain-aging cracking due to its formation and propagation during PWHT.