Abstract
Laser powder bed fusion (L‐PBF) of forming tools has become of major interest in the tooling industry because of the high geometrical flexibility of this process. During L‐PBF, a metallic powder bed is melted selectively by a laser beam, enabling the layer‐wise manufacturing of parts from 3D computer‐aided design data. The process is characterized by a locally and temporally unsteady heat flow in the solidified part and in the melt pool, causing nonequilibrium solidification and phase transformations. In addition, rapid heating and cooling occur, promoting the formation of microstructural defects, cold cracks, and distortion. Because of the high tendency to form cold cracks, processing of martensitic tool steels is still a challenging task. Tool steel X65MoCrWV3‐2 is processed by L‐PBF and the resulting microstructure and the associated local properties are investigated by microhardness measurements, nanoindentation, and scanning electron microscopy. It is gathered from the investigations that regions of different microstructures and mechanical properties on both micro‐ and macroscale are present in the L‐PBF‐densified steel. The different microstructures and properties are the result of the alternating heat insert at different temperature regimes, forming heat‐affected zones in which the tempering processes are triggered and strongly varying properties are generated.
Highlights
Laser powder bed fusion (L-PBF) of forming tools has become of major interest in tured tools
The L-PBF-built X65MoCrWV3-2 tool steel shows a heterogeneous microstructure, which is characterized by a hierarchical composition
As determined by energy-dispersive X-ray spectroscopy (EDS) measurements, mainly heavier elements, such as Mo, W, and V, segregate into the interdendritic spaces (Figure 2). This microstructure is attributed to the process-specific high cooling rates which act during L-PBF, favoring a fast solidification with strong constitutional undercooling effects and a limited diffusion of especially heavy elements like Mo or W.[18,22]
Summary
Martensitic secondary hardenable X65MoCrWV3-2 tool steel is investigated in L-PBF-built and laser-melted condition. For the characterization of the steel in L-PBF-built condition, gas atomized powder, provided by Deutsche Edelstahlwerke Specialty Steel GmbH & Co. KG, was processed with L-PBF. In addition to the L-PBF buildup, the influence of the melting of a single layer on the already solidified material was investigated. For this purpose, the surface of X65MoCrWV3-2 bulk material was melted with the laser of the L-PBF 100 device representing the densification of a single layer in the L-PBF-process. The exact values may not be mentioned here
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