Potential Causes for Cracking of a Laser Powder Bed Fused Carbon-free FeCoMo Alloy

Abstract

Compared to hot isostatic pressing or casting, laser-based powder bed fusion (LPBF) facilitates a near-net-shape fabrication of geometrically complex tools leading to a strongly reduced post-processing time and effort and consequently lower costs. Conventional tool steels are, however, prone to cracking during LPBF due to their high carbon equivalent numbers. In contrast, carbon-free maraging steels promise an enhanced processability due to the formation of a soft martensite, which is subsequently hardened by the precipitation of intermetallic phases.A novel maraging steel for cutting applications (Fe25Co15Mo (wt%)) has been developed in recent years, and the present contribution deals with the processability of this novel alloy as a candidate for LPBF. However, severe cracking has been observed despite its low carbon content. The scanning electron microscopy revealed transcrystalline cleavage fracture plains on the crack surfaces. It is assumed that silicon oxide inclusions, which were verified by energy dispersive X‑ray spectroscopy, are responsible for the brittle failure. The electron backscatter diffraction analysis revealed coarse elongated grains, which may also contribute to cracking. The differential scanning calorimetry could not confirm an influence of brittle ordered FeCo domains that are potentially formed during cooling. In conclusion, solution approaches for the fabrication of crack-free parts are presented.