Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the correlation between the processing strategy and the material properties remains mostly unclear. The process-inherent high cooling rates support the assumption that a very fine martensitic microstructure is formed. Therefore, the microstructure formation was studied by means of scanning electron microscopy, hardness measurements, and an analysis of the tempering stability. It could be shown that additively manufactured Bainidur AM samples possess a bainitic microstructure despite the high process-specific cooling rates in PBF-LB/M. This bainitic microstructure is characterized by an excellent tempering stability up to temperatures as high as 600 °C. In contrast to this, additively manufactured and martensitic-hardened specimens are characterized by a higher initial hardness but a significantly reduced tempering stability. This shows the potential of manufacturing products from Bainidur AM for high-temperature applications without the necessity of a post-process heat treatment for achieving the desired bainitic microstructure.

Additive manufacturing (AM) technologies, such as laser-based powder bed fusion of metals (PBF-LB/M), allow for the fabrication of complex parts due to their high freedom of design. PBF-LB/M is already used in several different industrial application fields, especially the automotive and aerospace industries. Nevertheless, the amount of materials being processed using AM technologies is relatively small compared to conventional manufacturing. Due to this, an extension of the material portfolio is necessary for fulfilling the demands of these industries. In this work, the AM of case-hardening steel 16MnCr5 using PBF-LB/M is investigated. In this context, the influences of different processing strategies on the final hardness of the material are studied. This includes, e.g., stress relief heat treatment and microstructure modification to increase the resulting grain size, thus ideally simplifying the carbon diffusion during case hardening. Furthermore, different heat treatment strategies (stress relief heat treatment and grain coarsening annealing) were applied to the as-built samples for modifying the microstructure and the effect on the final hardness of case-hardened specimens. The additively manufactured specimens are compared to conventionally fabricated samples after case hardening. Thus, an increase in both case-hardening depth and maximum hardness is observed for additively manufactured specimens, leading to superior mechanical properties.

Typical high-strength products are made from carbon-rich steels possessing relatively high carbon content, thus reducing weldability. In this work, preliminary studies on designing and tailoring a low-alloyed steel for the laser-based powder bed fusion (PBF-LB/M) process by adding carbon black (C) nanoparticles and tungsten carbide (WC) particles for enhancing the material properties are provided. First, the base material 16MnCr5 is modified with different concentrations of C and WC. It was found that an increased C and WC content resulted in an elevated material hardness in the as-built state. However, this comes at the cost of a poorer processability as pore formation increased for C-modified and crack tendency increased for WC-modified 16MnCr5. When applying a post-process quenching and optional tempering heat treatment, material hardness in the range of 615 HV can be achieved for C-enriched 16MnCr5 in the tempered state, which would be suitable for bearing and gearing applications. The addition of WC particles favored an improved wear resistance which is twice as high as the one of C-modified material for similar material hardness, showing the enormous potential of WC addition for reducing the wear rate. Complementary SEM and EDX analyses show that both the dilution and bonding zone of the WC particles are affected by the processing conditions and the WC concentration. Furthermore, it was found that a nearly defect-free fabrication of WC-enriched 16MnCr5 was possible for up to 2.5 wt.-% of WC, proving that the occurring defects are highly sensitive to the WC concentration.

Additive manufacturing (AM) methods become more and more important due to improvements in the printing technology and availability of printers. As additive manufacturing is still a very expensive technology, it is predominantly used for complex parts in aerospace or medical applications. Especially in such demanding applications the properties of the parts are very important. In case of M50NiL, a carburizing heat resistant steel typically used for mainshaft bearings in aero engines, the development of an AM process and the properties of AM processed parts are shown. By comparison with specimens manufactured from conventional M50NiL it is demonstrated, that properties determined by optical microscopy, hardness testing, tensile testing, and rolling contact fatigue testing of M50NiL AM and M50NiL conventional manufactured are comparable.

Low‐alloyed steels are used for a variety of different applications like bearings or gears. Additive manufacturing technologies like directed energy deposition (DED‐LB/M) allow for a fast and close‐to‐contour fabrication of sophisticated products without excessive waste of material. However, the DED‐LB/M process cannot be considered as state‐of‐the‐art for this group of materials. This study presents findings on the material properties of the additively manufactured low‐alloyed steel Bainidur AM by means of DED‐LB/M. This includes studies on the mechanical properties (hardness, compression strength) as well as the microstructural properties (scanning electron microscopy [SEM]). The microstructure in the as‐built state appears like a bainitic–martensitic one with shares of retained austenite which is not fully transformed during cooling. As a differentiation is barely possible from the SEM images, a plethora of investigations is further used to assess the microstructure. As‐built samples possess a good combination of ductility and hardness. Furthermore, the specimens are characterized by a good tempering stability up to 600 °C. This tempering stability is characterized by a homogeneous hardness of around 400 HV1 for all temperatures. In contrast, the conventionally hardened specimens show a drop‐off in material hardness, further indicating the excellent material properties of additively manufactured Bainidur AM.