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Tailoring the nanostructure of laser powder bed fusion additively manufactured maraging steel
Allam T., , Köhnen P., Marshal A., Schleifenbaum J.H., Haase C.
Published in Elsevier
Volume: 36
Grade 300 maraging steel specimens were synthesized using the additive manufacturing technique laser powder bed fusion (LPBF). The influence of heterostructures, i.e. cellular/dendritic regions with micro-segregations, formed during LPBF processing on the microstructure evolution, particularly the formation of nano-precipitates were investigated. We applied aging and solution- aging post heat-treatments to allow the precipitation in presence and after elimination of the heterostructures, respectively. A model describing the precipitation mechanisms and sequence for both heat-treatment routes is proposed based on the three-dimensional elemental distribution at near-atomic scale and the quantification of nano-scale segregated regions performed by atom probe tomography (APT). We observed that the heterostructures favored the austenite retention in the as-built condition, while they promoted the martensite-to-austenite reversion in the aged condition. On the contrary, the retention and reversion processes are suppressed in the solution-aged condition. The formation of nanosized (Ni,Fe,Co)3(Ti,Mo,Al) and (Fe,Ni,Co)7(Mo)6 precipitates was confirmed for both post heat-treatment routes. However, the nano-precipitates were smaller in size and higher in number density in the solution-aged condition, as compared to the aged state. The current work demonstrates that the elimination of heterostructures in the solution-aged condition, especially Ni micro-segregations, led to a high supersaturation and a concomitant increase in number density of (Ni,Fe,Co)3(Ti,Mo,Al) precipitates. The corresponding Ni-depleted matrix inhibited the martensite-to-austenite reversion. In contrast, the partial retention of heterostructures and the presence of retained austenite during aging without prior solution treatment resulted in a reduced number density of (Ni,Fe,Co)3(Ti,Mo,Al) precipitates, which can potentially trigger the reversion transformation supported by the rejection of Ni in front of (Fe,Ni,Co)7(Mo)6 precipitates. © 2020 Elsevier B.V.
About the journal
JournalData powered by TypesetAdditive Manufacturing
PublisherData powered by TypesetElsevier
Open AccessNo