Fatigue behavior of maraging steel fabricated by conventional route and Laser Powder Bed FusionTuesday (26.05.2020) 14:30 - 14:50
High strength steels, particularly maraging steels, are essential for injection mold and casting mold tools. Nowadays, these tools are produced by means of Laser Powder Bed Fusion (LPBF) process, which significantly expands design freedom and opens up new possibilities for shape optimization in comparison to conventional tools. With increasing knowledge of this innovative process technology, the interest on LPBF boosts in many industrial sectors. However, for safety-relevant technical applications a comprehensive understanding of the correlation between the fabrication process route, the resulting microstructure and the associated effects on mechanical properties are crucial. As a result, materials produced by additive manufacturing have become a key issue in the field of material characterization and testing. At first glance, the strength properties of additively manufactured (AM) materials are often considered as very promising, due to yield and tensile strength reaching the level of wrought material. Meanwhile, currently available fatigue results for AM materials provide quite a different picture. This, however, is not surprising, because the fatigue behavior is significantly influenced by minor changes in the microstructure. Effects such as the cyclical thermal entry and defect features, for instance, lack of fusion or micro-pores have a huge influence on the cyclic behavior of the material.
For the future application of AM materials, it is necessary to gain a detailed understanding of the likely discrepancies in failure mechanisms of cyclically loaded additively and wrought manufactured material. Establishing reliable process-structure-property correlations allows a shape-optimized component design and a safe operation during the component lifetime. This study will focus on results regarding the fatigue behavior and failure mechanisms of 18Ni300 maraging steel (1.2709) fabricated by the conventional route and LPBF technologies. Based on tests from low to very high cycle fatigue range realized with ultrasonic fatigue testing equipment, the influence of the fabrication route on the mechanical properties will be shown. From the results, it is concluded, that the durability of AM-maraging steel is sensitive to small defects.