Microstructure, Mechanical Properties and Fatigue Crack Growth Behavior of Gas Tungsten Arc Welding Welded Joint of the Hastelloy N Alloy

Hastelloy N alloy is an excellent oxidation and corrosion-resistant material, which is selected as the shell material for the main vessel of molten salt reactors (MSRs). In this work, we conducted double-sided gas tungsten arc welding (GTAW) on 4 mm thick Hastelloy N alloy plates to examine the microstructure and mechanical properties of the welded joints. The S-N curve was obtained by fatigue test. The experimental results show that fatigue cracks initiate along the weld toe and propagate inward in a fan-shaped pattern. The hardness is highest in the heat-affected zone (HAZ). The fracture mode observed was trans-granular. The plastic zone in the initial stages of crack propagation remained relatively minimal. However, it gradually expanded during subsequent stages of the process. It is noteworthy that the crack propagation process often involves the development of secondary cracks, accompanied by profound plasticity-induced closure effects. The results of our investigation demonstrate that the welded joint exhibits excellent fatigue performance.