Maraging steels such as 1.2709 are high strengthhigh toughness alloys that gain their exceptional mechanical properties by the combination of nanometer-sized intermetallic precipitates and a martensitic matrix. Here the martensitic microstructure is not achieved by a high carbon content but by adding nickel to the chemical composition. In turn, the lack of carbon leads to good weldability and therefore makes these materials preferred candidates for additive manufacturing techniques, such as selective laser melting (SLM). Applications for SLM produced components are found especially in the tooling industry, where the implementation of inserts with intelligent conformal cooling channels in dies and moulds has already shown to drastically increase the tool lifetime. In this study, different maraging steels are investigated with respect to typical powder characteristics, such as sphericity, particle size distribution, on the one hand, and the microstructure as well as the achieved mechanical properties of the respective SLM printed parts, on the other hand.

Additive manufacturing of steel powders has gained a lot of attention in recent years. In the early stages of Laser Powder Bed Fusion (L-PBF) of steel powders, the well-known materials 1.2709, 316L, and 17-4 PH were used due to their very low carbon content. Yet, since these materials are, on the one hand, quite soft (316L) but, in some cases, too highly alloyed for specific engineering applications (1.2709) on the other hand, also carbon steels are increasingly considered for a use in L-PBF processes. In general, it is well known that carbon limits the weldability of the steel materials. As a rule of thumb, steels with a carbon content below 0.22 wt.-% are suitable for L-PBF processes without powder bed preheating. This contribution presents a new carbon-steel alloy concept which can be processed by L-PBF without powder bed preheating. Due to the special alloy design, it will be shown that the printed parts are ready-to-use in the as-built state with a well-balanced property relationship of strength, ductility, and impact toughness. Apart from the usability in the asprinted condition, it will also be shown that an additional heat treatment or even a surface hardening process can be used to gain even better material and part properties compared to the as-built condition.