Triplex steel powder design to avoid hot cracking in laser-powder bed fusion using computational thermodynamics

High manganese steels offer exceptional combinations of high strength and ductility, resulting in weight reduction when utilized in structural applications. Nevertheless, the conventional manufacturing routes of these steels is hindered by many production problems. Additive Manufacturing (AM) has emerged as a reliable solution to fabricate thin or complex shape compounds using these steel grades. Indeed, several studies have demonstrated the success to fabricate high manganese twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) steels by laser-powder bed fusion (L-PBF). However, a recent study on a high manganese triplex steel composition has revealed the occurrence of both hot cracking and micro segregation during rapid solidification in L-PBF, highlighting potential processability issues of this family of high alloy steels. In this study, the hot cracking susceptibility of different triplex steels is evaluated, focusing on the impact of the composition on the solidification paths and final microstructures. A Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) approach is employed to predict alloy-dependent hot cracking susceptibility so as to establish guidelines for preventing hot cracking and provide insights into alloy design for AM. Microstructural observations are used to determine the accuracy of CALPHAD predictions in terms of elemental segregation, phase formation and hot cracking susceptibility. To this end, scanning transmission electron microscopy is used to evaluate elemental segregation at grain boundaries, while the local distribution of phases and their relative amount is measured by electron backscattered and X-ray diffraction, respectively. Hot cracking susceptibility is experimentally evaluated by measuring the length of cracks (when present) in the cross section of printed specimens.