Page 102 - MSAM-4-2

Materials Science in Additive Manufacturing Additively manufactured high carbon steel

without prior solutionizing. These results suggest that Conflicts of interest
martensite did not form during water quenching after
the solutionizing step but only developed during the Yongho Sohn serves as the Editorial Board Member of the
subsequent cryogenic treatment in LN . In addition, direct journal but was not in any way involved in the editorial
2
water quenching at 1050 or 1075°C is not expected to yield and peer-review process conducted for this paper, directly
lower bainite due to the inherently slow transformation or indirectly. The other authors declare they have no
competing interests. In addition, the views, opinions, and
kinetics. No evidence of lower bainite was observed in the conclusions made in this document are those of the authors
water-quenched microstructure.
and should not be interpreted as representing the official
Microsegregation in the as-printed microstructure policies, either expressed or implied, of the DEVCOM
leads to compositional variations between cellular and Army Research Laboratory or the U.S. Government. The
intercellular regions, which can significantly influence U.S. Government is authorized to reproduce and distribute
phase transformation behavior. As featured in Figure 1A, reprints for Government purposes notwithstanding any
TTT curves for a homogeneous matrix with varying copyright notation herein.
carbon content indicate that bainitic transformation is
not expected to occur at temperatures as low as 125°C Authors’ contributions
after 3 h. However, the segregation of carbon in the Conceptualization: Thinh Huynh, Yongho Sohn
40
form of carbides and substitutional alloying elements, Formal analysis: Thinh Huynh
such as Mo, Cr, Mn, and Si, to intercellular regions, 28,41,42 Investigation: Thinh Huynh, Kevin Graydon, Nicolas Ayers
as observed in Figure 3B, may dramatically alter the Methodology: Thinh Huynh, Yongho Sohn
bainite start temperature and incubation period. Thus, Validation: Kevin Graydon, Nicolas Ayers, Yongho Sohn
43
the microstructural heterogeneity induced by the rapid Writing – original draft: Thinh Huynh
solidification inherent to LPBF plays a critical role in Writing – review and editing: Yongho Sohn
altering transformation pathways, potentially enabling
bainite formation that would not be predicted based on Ethics approval and consent to participate
nominal compositions alone. Not applicable.

5. Conclusion Consent for publication
Additively manufactured high-carbon-bearing steel with Not applicable.
solidified austenite primed for phase transformations
was investigated for microstructural evolution. Excellent Availability of data
hardness, as high as 737 ± 31 HV, was achieved with
a liquid-nitrogen quench at room temperature for the All data associated with this publication are available upon
as-printed condition. The high-solutionizing temperature request from the corresponding author.
can be tailored to produce carbide or carbide-free matrices, References
and the amount of desired carbides could be controlled by
the temperature of the solutionizing treatment. A multi- 1. Mehta A, Zhou L, Huynh T, et al. Additive manufacturing
phase microstructure consisting of austenite, martensite, and mechanical properties of the dense and crack free
and bainite with excellent hardness was achieved by Zr-modified aluminum alloy 6061 fabricated by the laser-
powder bed fusion. Addit Manuf. 2021;41:101966.
altering the microstructure with heat treatments. Results
demonstrated that LPBF of high-carbon-bearing steels doi: 10.1016/j.addma.2021.101966
possess intriguingly controllable microstructures and a 2. Zhou L, Hyer H, Park S, et al. Microstructure and
wide range of mechanical properties that can be tailored to mechanical properties of Zr-modified aluminum alloy 5083
the desired application. manufactured by laser powder bed fusion. Addit Manuf.
2019;28:485-496.
Acknowledgments doi: 10.1016/j.addma.2019.05.027
None. 3. Zheng B, Zhou Y, Smugeresky J, Schoenung J, Lavernia E.

Funding Thermal behavior and microstructural evolution during
laser deposition with laser-engineered net shaping:
This research was sponsored by the DEVCOM Army Part I. Numerical calculations. Metall Mater Trans A.
Research Laboratory under a cooperative agreement 2008;39:2228-2236.
contract, W911NF1720172. doi: 10.1007/s11661-008-9557-7

Volume 4 Issue 2 (2025) 9 doi: 10.36922/MSAM025100011