Effects of Aging Temperature on Microstructure and Properties of Custom 455 PCTIG Welded Joints

Aiming at the problems of alloying element segregation and mechanical property degradation in PCTIG welded joints of Custom 455 maraging stainless steel, this study employed solution treatment as the pre-process, and systematic microstructural characterization and mechanical property tests were conducted on the joints treated at different aging temperatures(480 ℃, 520 ℃, 560 ℃), focusing on investigating the effect of aging temperature on the microstructure and mechanical properties of the joints. The results show that as the aging temperature increases from 480 ℃ to 560 ℃, the content of δ-ferrite in the joint gradually decreases, and its morphology gradually dissolves from vermicular to granular; meanwhile, the content of retained austenite increases progressively, with its morphology transforming sequentially from granular (480 ℃) to acicular (520 ℃) and then to continuous lamellar (560 ℃). The average hardness of the weld zone decreases from 526 HV to 400 HV, the tensile strength decreases from 1569 MPa to 1189 MPa, and the elongation increases from 6% to 12%. Mechanism analysis indicates that the reduction in δ-ferrite content can reduce the potential paths for crack propagation, thereby improving joint toughness; acicular retained austenite has a weak segmentation effect on the martensitic matrix, leading to a slight decrease in strength; continuous lamellar retained austenite forms a network structure, which significantly impairs the continuity of the martensitic matrix and results in a decrease in material strength. However, as a soft phase, continuous lamellar retained austenite can coordinate plastic deformation effectively and significantly enhance the continuous deformation capacity and fracture toughness of the material.