Page 94 - MSAM-4-2

Materials Science in

Additive Manufacturing

ORIGINAL RESEARCH ARTICLE
Phase transformations in additively

manufactured high carbon-bearing steel

Thinh Huynh , Kevin Graydon , Nicolas Ayers , and Yongho Sohn*
Department of Materials Science and Engineering, University of Central Florida, Orlando, Florida,
United States of America

Abstract
For high-carbon steels that are particularly sensitive to thermally induced phase
transformations, the rapid solidification rates inherent to laser powder bed fusion
(LPBF) offer a promising pathway to develop unconventional microstructures
directly in the as-printed state. This study demonstrates the formation of a
supersaturated austenitic matrix – engineered through carbon meta-stabilization
and rapid solidification for subsequent heat treatments to develop complex,
hierarchical microstructural constituents. A predominantly austenitic high-carbon
steel, decorated with cellular segregation networks, was successfully fabricated
using LPBF. Post-processing through cryogenic quenching and high-temperature
solutionizing treatment, followed by low-temperature tempering, yielded a wide
range of microstructures and hardness values. The cryogenically quenched sample
*Corresponding author: exhibited a mixed microstructure of martensite, retained austenite, and cellularly
Yongho Sohn segregated regions, achieving a hardness of 737 ± 31 HV. In contrast, the combination
(yongho.sohn@ucf.edu)
of solutionizing, cryogenic quenching, and tempering produced a multiphase matrix
Citation: Huynh T, Graydon K, consisting of martensite, bainite, and austenite, with a hardness of 700 ± 20 HV. The
Ayers N, Sohn Y. Phase
transformations in additively insights gained into phase transformations and microstructural evolution during
manufactured high carbon- LPBF, along with secondary hardening via heat treatment, provide a foundation for
bearing steel. Mater Sci Add developing tailored post-processing strategies for a broad class of hardenable steels
Manuf. 2024;4(2):025100011.
doi: 10.36922/MSAM025100011 produced by additive manufacturing.
Received: March 5, 2025
Keywords: High-carbon steel; Laser powder bed fusion; Additive manufacturing;
1st revised: April 10, 2025
Austenite; Martensite; Bainite
2nd revised: April 17, 2025
Accepted: April 18, 2025
Published online: May 15, 2025 1. Introduction
Copyright: © 2025 Author(s).
This is an Open-Access article Laser powder bed fusion (LPBF) additive manufacturing (AM) can produce
distributed under the terms of the engineering components with enhanced performance-to-weight ratio, refine the
Creative Commons Attribution microstructure through rapid solidification, and enable innovative design. However, not
License, permitting distribution,
and reproduction in any medium, all commercially available alloys are considered compatible with LPBF. Developmental
provided the original work is efforts for metallic alloys used in LPBF often face technical challenges in undesired flaw
properly cited. formation. Even some alloys deemed weldable in the traditional sense have exhibited
Publisher’s Note: AccScience cracking under rapid solidification and often require chemistry modification for crack
Publishing remains neutral with mitigation. Parts built by AM processes like LPBF experience a very specific thermal
1,2
regard to jurisdictional claims in 3
published maps and institutional history. Particularly for phase transformation-sensitive steels, rapid quenching from
affiliations. the liquid state could produce varying amounts of austenite and martensite across the

Volume 4 Issue 2 (2025) 1 doi: 10.36922/MSAM025100011