Priming Additively Manufactured Cobalt-free Maraging Steels for Improved Properties via Changes to As-Built Microstructure

Published

July 23, 2025

Author(s)

Alec Saville, Jake Benzing, Fan Zhang, Joseph Aroh, Jordan Weaver, Russell Evans, Nicholas Derimow, Samantha Webster, Nikolas Hrabe, Cassidy Allen, Newell Moser, May Martin, Jason Holm, Christin Aumayr, Tilman Seifert, Michael Hirtler

Abstract

Supply chain challenges and health concerns have spurred the development of new Co-free, Cr-containing maraging steels with several new alloys already commercialized. These alloys are a less expensive and more sustainable form of the currently used Co-containing maraging steels C300 and C350. However, Co-free, Cr-containing maraging steels exhibit reduced strengths after heat treatment compared to current Co-containing alloys. New processing pathways are required to create microstructures able to reach parity with existing Co-containing or Ti-strengthened maraging steels and enable their replacement with sustainable alternatives. This work looks at using changes to laser beam powder bed fusion (PBF-LB) build parameters of the Co-free, Cr-containing maraging steel M789 to alter the as-built microstructure and provide new avenues for reaching parity with existing Co-containing maraging steels. Modelling of the PBF-LB build process suggests considerable changes in thermal history, and thereby likely unique evolution in solidification and solid state microstructures. Characterization of as-built material however showed little-to-no impact of build parameters on the solid state or solidification microstructures, suggesting M789 and other alloys experience phase transformations that are resilient to build parameter selection. Differences in porosity content between parameter sets obscured any changes in material properties during uniaxial tension and hardness testing. Despite these defects, multiple parameter sets produced material with as-built tensile strengths comparable to C300 maraging steels, demonstrating M789 can be a feasible alternative of C300 in as-built material applications. Future considerations on using heat treatments and implementing HIP to remove porosity defects are discussed as avenues to identify processing routes which boost the mechanical properties of M789 and other Co-free, Cr-containing alloys. Future work on better understanding the solid state transformations of M789 are also discussed, especially with implications on the resilience of this alloy to changes in build parameters and the development of other AM-resilient alloys.

Citation

NIST Interagency/Internal Report (NISTIR) - 8582

Report Number

8582

NIST Pub Series

NIST Interagency/Internal Report (NISTIR)

Pub Type

NIST Pubs

Download Paper

https://doi.org/10.6028/NIST.IR.8582

Local Download

Citation

Saville, A. , Benzing, J. , Zhang, F. , Aroh, J. , Weaver, J. , Evans, R. , Derimow, N. , Webster, S. , Hrabe, N. , Allen, C. , Moser, N. , Martin, M. , Holm, J. , Aumayr, C. , Seifert, T. and Hirtler, M. (2025), Priming Additively Manufactured Cobalt-free Maraging Steels for Improved Properties via Changes to As-Built Microstructure, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/NIST.IR.8582, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959903 (Accessed July 27, 2025)