Additive manufacturing (AM) technologies of metals, such as the widely used laser powder bed fusion (LPBF), enable the layer-by-layer fabrication of complex-shaped components. This versatile manufacture technology is hence particularly advantageous for tooling applications with their intricate shape. Medium and high carbon steels are used for tooling and their LPBF fabrication is challenging, due to evolving residual stresses eventually leading to pronounced cracking. Residual stresses are inherent to the LPBF process on its own and can additionally stem from the austenite-to-martensite transformation tool steels.

In this study, we have successfully developed a novel high-strength medium-carbon tool steel which can be processed without pre-heating the substrate plate by LPBF into crack-free and highly dense parts. The microstructure of the as-built microstructure of the steel is composed of martensite and residual austenite, as analyzed by optical and scanning electron microscopy, electron backscatter diffraction and X-ray diffraction. Residual austenite is transformed to martensite during loading imparting the transformation induced plasticity (TRIP) effect which causes work-hardening behavior. Owing to also the TRIP effect, the LPBF-fabricated steel showed good mechanical properties including high ultimate compressive stress of 3056 MPa, yield strength of 1330 MPa, and excellent impact toughness of 12.66 J.