Motivation and aim
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 steel obtains a limited hot hardness, which is of utmost importance during molding or hot forming operations. Thus, another martensitic steel is required for the SLM process, which satisfies this expectation. In this project, W360 Isobloc will be processed, the microstructure will be investigated, and mechanical properties will be characterized. This high molybdenum-chromium-vanadium 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. Within this project, the QT steel 1.6773 will be processed and analyzed.
Both steels, the martensitic steel W360 and the QT steel 1.6773, 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 liquidation cracks as well as solidification 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 processed within this project will be the CoCr-alloy Stellite 6. Generally, stellite 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.
 Holzweissig MJ, Taube A, Brenne F, Schaper M, Niendorf T. Microstructural Characterization and Mechanical Performance of Hot Work Tool Steel Processed by Selective Laser Melting. Metall and Materi Trans B 2015;46(2):545-9.
 Yadroitsev I, Sumrov I, Selective laser melting technology: from the single laser melted track stability to 3D parts of complex shape, Physics Procedia 2010, 5, 551-60.