Microstructural evolution and mechanical property response of additively manufactured 17-4 PH stainless steel under various heat treatment conditions

In the present study, the influence of different heat treatment conditions on the microstructure, hardness, and tensile properties of additively manufactured 17-4 PH stainless steel produced via the Laser Powder Bed Fusion (LPBF) process was systematically investigated. The fabricated samples were subjected to solution annealing (SA), direct aging, and double aging treatments to establish correlations between microstructural evolution and mechanical performance. Hardness and tensile properties were compared with those of conventional 17-4 PH stainless steel under the same heat treatment conditions. The LPBF-processed samples exhibited no notable improvement in UTS under direct aging, maintaining a value of approximately 1136 MPa, comparable to the As-Built condition. However, prolonged aging for 24 hours led to the highest UTS of 1420 MPa in LPBF samples, along with a ductility of 13.6%. Hardness measurements revealed that peak hardness in LPBF samples was achieved after SA, followed by 12 hours of aging, with a value of 428.68 HV. The martensite fraction increased after SA, decreased after aging, and remained constant throughout the aging duration. Among all the strengthening mechanisms, precipitation strengthening plays a crucial role in the strength of 17-4 PH stainless steel. Overall, the results highlight the distinct response of LPBF-processed 17-4 PH stainless steel to heat treatment compared with its conventionally processed counterpart, emphasizing the critical role of tailored aging conditions in optimizing mechanical properties.