Potential causes for cracking of a laser powder bed fused carbon-free FeCoMo alloy

Laser powder bed fusion (LPBF) facilitates near-net-shape fabrication of geometrically complex tools. This leads to significantly reduced post-processing effort compared to conventional manufacturing, for example in the case of hobbing cutters. However, due to the high carbon equivalent of high-speed steels, cracking of the brittle carbon martensite is very likely during LPBF. In contrast, carbon-free maraging steels promise enhanced processability due to the formation of a soft martensite. Hardening of the latter is guaranteed by the precipitation of intermetallic phases. A novel maraging steel for cutting applications (Fe25Co15Mo (weight%)) has been developed in recent years. This alloy might therefore be a candidate for LPBF. In the present work, the LPBF processability of this novel cutting alloy was investigated. Despite its low carbon content, severe cracking has been observed. The crack surface analysis revealed transcrystalline cleavage fracture. It is assumed, that silicon oxide inclusions on the crack surface are responsible for this brittle failure. Additionally, epitaxially elongated coarse grains were found, which may also contribute to cracking. An influence of brittle ordered FeCo domains, that are potentially formed during cooling in the LPBF process, could not be confirmed. Based on the obtained findings, solution approaches for the fabrication of crack-free parts are presented