Microstructures and mechanical properties of T92/Super304H dissimilar steel weld joints after high-temperature ageing

T92/Super304H dissimilar steel weld joints, fabricated through a gas tungsten arc welding (GTAW) technique using a Ni-based welding wire of ERNiCrMo-3, were aged at 650 °C for time up to 3000 h. Microstructures, fractographies and mechanical properties of the joints were then investigated. The results show that as the aging time increased, in the T92 side heat-affected zone (HAZ) and base metal (BM), the second-phase particles aggregate and coarsen along the austenite grain boundaries/in the austenite grains. In the Super304H side HAZ and BM, the growth of the austenite grains and that of the second-phase particles are slight. The fracture positions of the aged joints are always in the T92 BM. The tensile strengths and the hardness values of the joints drop firstly, then rise, and finally tend to be stable. The impact toughness values of the joints are monotonously decreases with the ageing time.