Effect of aging on microstructure and mechanical properties of dissimilar steel welded joints between G115 and Sanicro25 steel

This paper studied the high-temperature stability of dissimilar steel welded joints between G115 and Sanicro25 steel. The joints were exposed to 700 °C for time up to 2000h. The microstructure evolution of base metal (BM) and fine-grain heat-affected zone (FGHAZ) were analyzed. Tensile, microhardness, and impact experiments were conducted on the joints, and the explanations for the changes in mechanical performance are derived from the microstructure. The results showed that the Laves phase were precipitated after aging for 100 h, which has two nucleation methods. Nucleation adjacent to M₂₃C₆ is the main way in this research. Laves phase mainly grows up to consume M₂₃C₆. The microstructure in BM and FGHAZ is obviously different after aging. After aging for 1000 h, mechanical properties such as tensile strength, Vickers hardness, impact energy, elongation and area reduction are reduced, except for the yield strength. The softening caused by the microstructure evolution of FGHAZ is the main reason for the joint fracture in FGHAZ.