Insights into the Transformation-Induced Plasticity (TRIP) Effect in Ti-Free Grade 300 Maraging Steel Manufactured by La

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https://doi.org/10.1007/s11837-020-04425-9  2020 This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply

ADDITIVE MANUFACTURING FOR ENERGY APPLICATIONS

Insights into the Transformation-Induced Plasticity (TRIP) Effect in Ti-Free Grade 300 Maraging Steel Manufactured by Laser Powder Bed Fusion (LPBF) RANGASAYEE KANNAN

1,2

and PEEYUSH NANDWANA1,3

1.—Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA. 2.—e-mail: [email protected]. 3.—e-mail: [email protected]

The near-net fabrication capabilities of laser powder-bed fusion (LPBF) offer the potential to manufacture tools with complex cooling channels that can improve the production efficiency of the tools with reduced greenhouse gas emissions. High strength, toughness, and wear resistance are some of the key properties required by the tooling industries to qualify tools. While strength can be increased through appropriate heat treatments, the increase in strength comes with an associated ductility loss. We show that the nonequilibrium conditions inherent to LPBF can suppress the transformationinduced plasticity effect to room temperature in a Ti-free version of grade 300 maraging steel (G300MS), which is commonly not observed at room temperature in G300MS manufactured using conventional methods. The presence of retained austenite along with Ni-rich regions was found to increase the kinetics for austenite reversion during aging, thereby enabling the transformation of austenite into e martensite during tensile deformation at room temperature, in turn increasing the strength with minimal ductility loss.

INTRODUCTION Martensitic transformation, precipitation, and austenite reversion are some of the key solid-state phase transformations in maraging steels during thermal cycling.1 While in most cases, the solidstate phase transformations determine the mechanical properties of the parts,2–6 deformation-induced phase transformations also play an important role in determining the mechanical properties, for

Notice of Copyright: This manuscript has been authored by UTBattelle, LLC, under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). (Received July 21, 2020; accepted September 29, 2020)

example, the elongation to failure and strength. It has been hypothesized that austenite reversion during aging in Mn-based maraging steels is responsible for increasing the elongation at failure by a transformation-induced plasticity (TR