Citation: Metalnikov, P.; Ben-Hamu, G.; Eliezer, D. Hydrogen Trapping in Laser Powder Bed Fusion 316L Stainless Steel. Metals 2022, 12, 1748. https://doi.org/10.3390/ met12101748 Academic Editor: Francesco Iacoviello Received: 29 August 2022 Accepted: 13 October 2022 Published: 18 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Article Hydrogen Trapping in Laser Powder Bed Fusion 316L Stainless Steel Polina Metalnikov 1,2 , Guy Ben-Hamu 2, * and Dan Eliezer 1 1 Department of Material Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel 2 Department of Mechanical Engineering, Sami Shamoon College of Engineering, Ashdod 77245, Israel * Correspondence: guy@sce.ac.il; Tel.: +972-547787911 Abstract: In this study, the hydrogen embrittlement (HE) of 316L stainless steel produced by laser powder bed fusion (L-PBF) was investigated by means of hydrogen trapping. The susceptibility of the material to HE is strongly connected to the interaction of hydrogen atoms with volumetric defects in the material. Trapping hydrogen in those defects affects its availability to critical locations where a hydrogen-induced crack can nucleate. Therefore, it is important to study the characteristics of hydrogen traps to better understand the behavior of the material in the hydrogen environment. The hydrogen was introduced into the material via electrochemical charging, and its interactions with various trapping sites were studied through thermal desorption spectroscopy (TDS). The obtained results were compared to conventionally produced 316L stainless steel, and the correlation between microstructure, characteristics of hydrogen traps, and susceptibility to HE is discussed. Keywords: hydrogen embrittlement; 316L stainless steel; additive manufacturing; hydrogen trapping; thermal desorption spectroscopy 1. Introduction Austenitic stainless steels (ASSs) are characterized by good mechanical properties, ex- cellent formability, toughness, and corrosion resistance, both at low and high temperatures. This is the prevalent family of stainless steel (SS) in terms of usage and number of alloys [1]. ASS, and particularly stable ASS, e.g., 316 and 316L, are also considered to be fairly resistant to hydrogen-induced damage and hydrogen embrittlement (HE), especially compared with ferritic and martensitic SS [1–4]. The enhanced resistance to HE of ASS is usually attributed to the lower diffusivity and higher solubility of hydrogen in the fcc γ-austenite phase [5], as well as to the retarded transformation of γ to strain-induced martensite [6–8]. Nowadays, ASS can be produced by various additive manufacturing (AM) technolo- gies. These technologies possess the unique ability of the production of complex shaped parts in a relatively short time. One of the most common AM processes is laser powder bed fusion (L-PBF). During the L-PBF process, a thin layer of powder is spread on the build platform and then selectively melted by a high-energy laser beam [9–11]. This results in very high cooling rates, and the microstructure of L-PBF ASS, particularly 316L, is reported to consist of relatively fine austenite grains with irregular shape and a metastable cellular sub-grain structure [12–17]. As a result, L-PBF ASS usually presents improved strength and ductility in comparison to conventionally produced counterparts [17–20]. The susceptibility of L-PBF ASS to HE has been studied recently by various re- searchers [21–24]. In general, hydrogen is reported to have little negative effect on L-PBF ASS. This is attributed to the unique microstructure of the material, produced by L-PBF. For instance, it was proposed by Kong et al. [21] that the fine cellular structure formed in L-PBF 316L SS can restrict the generation of twins, resulting in a lower possibility of martensite transformation during hydrogen charging. The sub-grain boundaries might provide rapid transportation channels for hydrogen atoms, hence increasing the diffusion rate [22]. Melt Metals 2022, 12, 1748. https://doi.org/10.3390/met12101748 https://www.mdpi.com/journal/metals