Lean tool steel processed via laser powder bed fusion: in situ observation of transformation induced plasticity

The high industrial demand for sustainable tooling concepts is a strong driving force for the development of lean steels and manufacturing processes. Thereby, additive manufacturing has been gaining momentum in tool and mold manufacturing for several years due to its ability to create complex designs in significantly shorter time than traditional processing methods, often at a reduced cost. This study presents a lean Fe92.65Cr4.2V2.1B0.05C1 (wt.%) cold-work tool steel processable via laser powder bed fusion (PBF-LB/M) without additional substrate plate heating. In the as-built state, a microstructure composed of austenite, martensite, V-rich carbides and a B-enriched phase was concluded from investigations with electron backscatter diffraction, X-ray diffraction and transmission electron microscopy. This complex microstructure provides a high ultimate compressive strength of 4935 ± 101 MPa, adequate compressive fracture strain and a pronounced work hardening. In particular, the work hardening can be also ascribed to the transformation of retained austenite into martensite, in the means of transformation induced plasticity (TRIP) effect, which was demonstrated by in situ synchrotron measurements during quasi-static compression testing. Such a martensitic transformation was also detected after pin on disc experiments, promoting a superior performance of Fe92.65Cr4.2V2.1B0.05C1. In comparison to a commercial high alloyed cold-work tool steel (1.2379) which was tested under identical conditions, the lean steel fabricated by PBF-LB/M, revealed higher ultimate compressive strength under quasi-static compression load, similar compressive fracture strain and a significantly enhanced abrasive wear resistance. Therefore, the PBF-LB/M-fabricated lean steel offers significant potential as resource-efficient material for tooling applications. • Developed lean Fe-Cr-V-B-C steel processable by laser powder bed fusion. • Improved sustainability due to reduced amount of critical raw elements. • High compressive strength and wear resistance compared to industrial 1.2379. • Martensitic transformation shown via in situ synchrotron study during compression.