Heat-induced effects and cracking susceptibility in gas tungsten arc welding of Inconel 939 superalloy using Inconel 625 filler metal

Abstract

This study examines the effect of heat input on crack formation in the heat-affected zone (HAZ) during gas tungsten arc welding (GTAW) repair of Inconel 939 superalloy. The workpiece, which had been in service for 100,000 h before requiring repair, underwent pre-welding heat treatment to enhance weldability. Repair welding was conducted using four different heat inputs. The results revealed that heat inputs below 0.298 kJ/mm led to lack of fusion at the weld pool root. Additionally, Inconel 939 exhibited high sensitivity to heat-affected zone (HAZ) cracking, with most cracks initiating in the partial melting zone (PMZ). Alloying element segregation in this region formed low melting point phases, creating a liquid film along crack boundaries confirming liquation cracking as the dominant mechanism. A direct correlation was established between heat input and liquation crack formation in the HAZ. Higher heat inputs increased both HAZ hardness and crack density. This study aims to optimize the gas tungsten arc welding (GTAW) process for Inconel 939 by identifying the maximum allowable heat input that minimizes HAZ defects while ensuring fusion integrity.

Keywords

• Inconel 939 superalloy
• Heat input
• Liquation cracks
• Crack susceptibility
• Hardness
• Repair welding