Mechanical Properties and Microstructure of Laser Powder Bed Fusion‐Processed 18Ni300 Maraging Steel According to Direct Aging Treatment Conditions

The nonequilibrium microstructures produced by laser‐based additive manufacturing can enhance the mechanical properties of metallic alloys. However, the optimal post‐treatment conditions will change according to the initial microstructure induced by the manufacturing process employed. Therefore, this study investigates the optimal direct aging conditions for the post‐treatment of laser powder bed fusion‐processed 18Ni300 maraging steel by changing the aging temperature and time. The aging time required to achieve maximum tensile strength decreased as the aging temperature increased, and an increase in the aging temperature accelerated the evolution of nanoscale precipitates. The results indicate that the optimal direct aging conditions of 520 °C for 2 h achieved the largest tensile strength (≈2100 MPa) and precipitate area fraction. Notably, the reduced aging time at this temperature compared with that under conventional aging conditions (8 h at 460 °C or 490 °C) minimizes the thickening of the (Mo,Ti)‐rich segregation, which otherwise contributes to austenite reversion and strength reduction owing to overaging. Thus, the optimal direct aging conditions for additively manufactured maraging steel components are different from those for conventionally produced maraging steel components. This understanding of the microstructural changes induced by direct aging according to the initial non‐equilibrium state provides vital information for enhancing the performance of additively manufactured metallic alloys.