Enhanced ductility of a 18Ni-300 maraging steel produced by directed energy deposition using cyclic austenitisation.

This study focuses on maraging steel 18Ni-300 produced using directed energy deposition (DED). Electrical resistivity was successfully implemented to investigate the α′↔γ transformation during the austenitisation heat treatment. It was found that this transformation occurs in two steps: the first is governed by a diffusion-controlled mechanism involving local equilibrium with partitioning (PLE), while the second involves local equilibrium with negligible partitioning (NPLE). Thanks to the resistivimetric study, the transformation kinetics were monitored and compared between the DED alloy and a wrought reference sample. The two-steps transformation induces chemical segregation in the microstructure, which can be reduced by holding the sample at high temperature or, conversely, enhanced through short austenitic cycling, as demonstrated in this study. Applying five cycles of 15 min at 820 °C to the DED-processed steel resulted in both microstructural refinement and an increase in austenite content, which reached 5.3 vol %. This treatment also induced a significant increase in the ductility of the DED alloy, despite its anisotropy.