Quenched and tempered (Q&T) steels, exemplified by the low alloyed structural steel grade 42CrMo4 (AISI 4140), offer relatively high strength, hardness and wear-resistance combined with a comparatively good toughness. These steels find widespread applications, particularly in toolmaking due to their cost-effectiveness. Addressing the demands of cost and resource-efficient manufacturing of complex components with desired mechanical properties, especially regarding individual products and small series, correspondingly requires innovative solutions. Near-net shape additive manufacturing (AM) processes, such as electron beam-based powder bed fusion of metals (PBF-EB/M), represent promising techniques to overcome prevailing challenges as these processes reduce costs considerably, especially for small series, through minimized subsequent machining steps. However, investigations regarding the manufacturing of the low-alloyed Q&T steel 42CrMo4 (AISI 4140) by the PBF-EB/M process remain limited. The present study thus focuses on assessing the structural integrity of 42CrMo4 (AISI 4140) Q&T steel manufactured via PBF-EB/M technique.

A stable processing window was obtained to fabricate near-fully dense 42CrMo4 (AISI 4140) components. The relative density was determined by means of optical microscopy and micro-computed tomography. In addition, process parameters such as beam current and scanning speed were varied to adjust microstructures and mechanical properties. For the latter, cylindrical tensile specimens were used for characterization. Furthermore, the effect of post-processing heat treatments on the final material properties was investigated. Microstructural features and mechanical behaviour, including hardness, quasi-static as well as fatigue properties, were evaluated for the as-built and selected heat-treated conditions. Finally, these results were compared to those of conventional manufactured 42CrMo4 (AISI 4140). The presented study contributes to the understanding of additive manufacturing of high-strength steels and shows the capability of processing 42CrMo4 (AISI 4140) steel by PBF-EB/M with tailored microstructural and mechanical properties. Combining the high-strength and wear-resistance properties of a Q&T steel with the advantages of AM in terms of design flexibility and shortened lead times enables the usage of 42CrMo4 in demanding engineering applications.