Additive manufacturing of medium carbon steels and a CoCr-alloy

The project addresses the fabrication and analysis of three challenging materials via selective laser melting (SLM). Two medium carbo steels and a high carbon content CoCr-alloy are chosen in order to expand the material spectrum available for SLM. During this one-year project, thorough parameter-studies will be conducted to determine suitable parameter-sets. Additionally, preliminary microstructural and mechanical results will be obtained.

­­Since a decade, selective laser melting (SLM) has gained significant attention from academia and industry. This powder-bed based technology enables the manufacturing of highly complex and filigree parts in a near-net-shape manner with a relative density of approximately 99.9 %. However, the material spectrum available for SLM must be extended in order to further industrialize the process. So far, almost all research has addressed austenitic-, precipitation hardenable stainless-, maraging-, and martensitic steels. With regard to the latter material group, the martensitic steel
H13 (1.2344) is widely known for the additive manufacturing of components, primarily tools. Despite this, medium carbon steels obtain a limited hot hardness, which is of utmost importance during molding or hot forming operations. Thus, another martensitic steel is needed qualified for SLM processing, which satisfies this expectation. In this project, the microstructure will be investigated, and mechanical properties will be characterized. This tool steel is suited for applications in which highest toughness and hot hardness is needed, i.e., in cold work, hot work, and plastics tools. One further medium carbon steel group, which has rarely been investigated, can be identified as quenched and tempered (QT) steel. These steels exhibit high toughness accompanied by high strength. Thus, QT steels are employed in machinery and structures in which an increased yield strength and an abrasion resistance is demanded, e.g., as gears, cutting edges, or camshafts. Both steels possess medium carbon contents of approximately 0.5 wt.%, which has not successfully been processed at larger diameters, e.g., >50 mm. Evolving high residual stresses lead to numerous cracks during SLM fabrication. A promising approach to avoid the undesired cracks is the modification of the scan-strategy in combination with the variation of the build platform temperature up to 400 °C. The third material selected within this project is the CoCr-alloy with a high carbon content. Generally, these materials possess superior tribological and corrosion properties under aggressive conditions. Until now, these materials are processed by casting methods or powder metallurgy. Nonetheless, based on the processing technologies available, the geometrical freedom is restricted, and the machining is extremely challenging.