Key Takeaways & Executive Findings
- •• A modified heat treatment for additively manufactured Custom 465 achieves tensile strength comparable to wrought material, with UTS of 1773 MPa, YS of 1686 MPa, and elongation of 6.5%. • Atom probe tomography reveals that Mo atoms segregate to Ni3Ti precipitate surfaces, inhibiting precipitate growth and contributing to enhanced strength. • The study systematically investigates the effects of hot isostatic pressing, solution treatment, cryogenic treatment, and aging on microstructure and mechanical properties of L-PBF C465. • A validated yield strength calculation model is proposed, offering a predictive tool for designing heat treatments to meet diverse industrial requirements.
Abstract
Custom 465 (C465) is a martensitic stainless steel known for its high strength, toughness, and corrosion resistance, widely used in aerospace, automotive, and medical industries. However, limited work has been conducted on its additive manufacturing (AM) and no dedicated heat treatments have been developed for additively manufactured C465 to optimize its strength–ductility trade-off. In this work, the C465 was fabricated via laser powder bed fusion. The effect of hot isostatic pressing, solid solution, cryogenic treatment (−78.5°C), and aging on the composition homogenization, austenite-to-martensite transition, and Ni3Ti precipitation were systemically investigated. The atom probe tomography analysis reveals that Mo atoms accumulate on Ni3Ti precipitate surfaces and inhibits the Ni3Ti growth, contributing to the enhanced strength of C465. The modified heat treatment for additively manufactured C465 reaches comparable tensile strength with the wrought counterpart, yielding an ultimate tensile strength of 1773 MPa, yield strength of 1686 MPa, and elongation of 6.5%. A yield strength calculation model was proposed and validated with measured strength under various heat treatments, providing valuable insight for heat treatment design towards diverse industrial applications.
1. Introduction
Custom 465 (C465) is an ultrahigh-strength precipitation hardening (PH) stainless steel, which has been widely used in aerospace, automotive, and medical industries due to its superior combination of strength, toughness, and corrosion resistance compared with other high-strength PH steels [1]. For example, C465 is considered a superior alternative to the 35NCD16THQ material used for landing gear on Airbus A320 family, due to its high tensile strength and fracture toughness [2]. Additionally, C465 is used in automotive applications such as suspension coil springs, engine valve springs, where high plasticity and corrosion resistance are essential. However, due to the increased complexity of components in various industries, conventional methods such as forging and machining are not able to meet the increased demand from industry.
Laser powder bed fusion (L-PBF), which enables the fabrication of complex geometries, has gained significant attention in various industries, such as in aerospace and medical sectors [3–8]. However, research on the fabrication of C465 using L-PBF is limited. Liu et al. [9] investigated the microstructure and mechanical properties of the C465 processed via L-PBF. After heat treatment suggested by the steel developer (Carpenter technology) for conventionally wrought C465, the additively manufactured C465 exhibits mechanical properties comparable to that of the wrought counterpart (ultimate tensile strength (UTS) = 1780 MPa, yield strength (YS) = 1684 MPa, elongation (El) = 9%). Sun et al. [10] studied the cracking and mechanical behavior of C465 processed via L-PBF. They added TiN particles into the C465 powders and suppressed cracking. After annealing, the C465 with 1.5wt% TiN particles have a lower UTS of 1100 MPa, but a higher ductility of 20%. While these studies used the heat treatment guidelines for conventionally wrought C465, the influence of heat treatment modifications on L-PBF processed C465 remains unclear. Previous work by Ifergane et al. [11] examined the effects of aging time and temperature on Ni3Ti precipitation in conventionally forged C465. However, it is still uncertain whether the same heat treatment processes are optimal for L-PBF C465 or if modifications could enhance its mechanical properties. According to literature [11] and technical datasheet [12], the current heat treatment of wrought C465 consists of solution treatment, cryogenic treatment, and aging. It is still unknown whether these heat treatment stages are optimal for the additively manufactured C465 and whether there is a possibility to shorten or simplify the process, such as skipping cryogenic treatment which is practically not plausible, in order to be more efficient and economical. Given the widespread use of C465 and the advantages of L-PBF in producing complex components, there is significant value in optimizing the heat treatment of L-PBF processed C465 to tailor its mechanical properties for specific industrial applications. Therefore, this study aims to investigate the effects of modified heat treatment on the microstructure and properties of C465, thereby providing customized heat treatment solution.
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Xiaohong Qi, Xiaokang Liang, Xin Li, Mingyang Ma, Xinhai Zou, Guichuan Li, Zhuangzhuang Liu, Kim Vanmeensel (2025). Tailoring the mechanical properties of additively manufactured Custom 465 martensitic stainless steel through heat treatment modification. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3168-9
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Frequently Asked Questions
What is the main objective of this study?
The study aims to investigate the effects of modified heat treatments on the microstructure and mechanical properties of additively manufactured Custom 465 stainless steel, with the goal of optimizing its strength-ductility trade-off and providing customized heat treatment solutions for industrial applications.
What heat treatment stages were examined?
The study examined the effects of hot isostatic pressing, solid solution treatment, cryogenic treatment at -78.5°C, and aging on the composition homogenization, austenite-to-martensite transition, and Ni3Ti precipitation.
What were the key mechanical properties achieved?
The modified heat treatment yielded an ultimate tensile strength of 1773 MPa, yield strength of 1686 MPa, and elongation of 6.5%, which are comparable to the wrought counterpart.
What role did Mo atoms play in the strengthening?
Atom probe tomography revealed that Mo atoms accumulate on Ni3Ti precipitate surfaces and inhibit Ni3Ti growth, contributing to enhanced strength.
Is there a model to predict yield strength?
Yes, a yield strength calculation model was proposed and validated with measured strength under various heat treatments, providing a predictive tool for heat treatment design.
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