metals Article Build Strategy and Impact Strength of SLM Produced Maraging Steel (1.2709) Anders E. W. Jarfors 1, * , Akash Chikke Gowda Hosapalya Shashidhar 1 , Hrushi Kailash Yepur 1 , Jacob Steggo 1 , Nils-Eric Andersson 1 and Roland Stolt 2   Citation: Jarfors, A.E.W.; Shashidhar, A.C.G.H.; Yepur, H.K.; Steggo, J.; Andersson, N.-E.; Stolt, R. Build Strategy and Impact Strength of SLM Produced Maraging Steel (1.2709). Metals 2021, 11, 51. https://doi.org/ 10.3390/met11010051 Received: 20 October 2020 Accepted: 21 December 2020 Published: 29 December 2020 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2020 by the authors. Li- censee 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/). 1 Department of Materials and Manufacturing, School of Engineering, Jönköping University, P.O. Box 1026, 551 11 Jönköping, Sweden; hoak18ga@student.ju.se (A.C.G.H.S.); yehr18po@student.ju.se (H.K.Y.); jacob.steggo@ju.se (J.S.); nils-eric.andersson@ju.se (N.-E.A.) 2 Department of Product Development, School of Engineering, Jönköping University, P.O. Box 1026, 551 11 Jönköping, Sweden; roland.stolt@ju.se * Correspondence: anders.jarfors@ju.se Abstract: The current paper aimed to study the impact properties of additively manufactured maraging steel (1.2709) using laser powder bed fusion (PBF-L) processing. The specimens were fabricated using 3D Systems ProX 300 equipment under constant specific power input, or Andrew number. The interactions between the build strategy and parameters such as hatch spacing and scan speed was, and the impact strength and fracture were investigated. The impact energy anisotropy was also investigated in parallel and perpendicular to the build direction. Instrumented impact testing was performed, and the fractography supported that the fusion zone geometry dictated the fracture behavior. The influence from gaseous elements such as nitrogen, oxygen, and hydrogen was found insignificant at the levels found in the printed material. Keywords: additive manufacturing; impact energy; fracture; hatch spacing; scan speed; process parameters 1. Introduction 1.1. Additive Manufacturing Thermal Processing Additive manufacturing (AM) is capable of manufacturing parts, products, and assem- blies with complex geometries and a great degree of design freedom [1]. Maraging steels are commonly used in aerospace and tooling industries due to the mechanical properties and the AM process offers suitable capabilities for the limited series size and necessary geometry capability [2] AM processed materials may display greater strength, but this may be associated with a reduction of ductility and toughness [3]. AM processing such as selective laser melting (SLM) of maraging steels results in a martensitic matrix [2]. In SLM processing, the metal powder is spread in a layer with a certain thickness or build-height, typically 30–50 μm. The layer thickness significantly impacts porosity and toughness. [4]. Oxidation of the material during SLM processing is managed by allowing an inert gas to flow over the powder bed such as argon and nitrogen [5]. The ability to form a dense material has been studied by, for instance, Ciurana et al. [6] and De Souza et al. [7], where the definition of volumetric specific energy or Andrew number, E d was used. A minimum value of the Andrew number is required to generate a dense material depending on the alloy composition. The Andrew number combines laser power, P, scan speed, v, hatch spacing, h, and build height, δ, into a characteristic measure, E d , as: E d = P vhδ (1) Metals 2021, 11, 51. https://doi.org/10.3390/met11010051 https://www.mdpi.com/journal/metals