Controlling Microstructure And Mechanical Properties Of Additively Manufactured High-Strength Steels By Tailored Solidification

The development of novel alloys specifically designed for additive manufacturing (AM) is a key factor in using the full potential of AM. This study addresses the design of advanced high strength steels (AHSS) that take advantage of the processing conditions during AM by laser powder bed fusion (LPBF). The alloy screening was guided by computational alloy selection (combined CALPHAD, Scheil-Gulliver, and phase-field simulations) and by rapid processing using powder blends (X30Mn21 steel and Al). Increasing Al contents, ranging from 0 to 5.4 wt. %, promoted bcc-fcc solidification, and allowed for tailoring the stacking fault energy (SFE). On the one hand, the transition from fcc to bcc-fcc solidification enabled controlling the microstructure and texture evolution during AM. On the other hand, the wide SFE range between 8 J/m(2) (0 wt. % Al) and 44 J/m(2) (5.4 wt. % Al) promoted flexible adjustment of the active deformation mechanisms, including transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), to govern the work-hardening behavior. The microstructure after LPBF and after plastic deformation was analyzed by XRD, SEM, EDX, EBSD, EPMA, and TEM. Mechanical properties of bulk specimens and lattice structures were analyzed using tensile and compression testing with a focus on energy absorption capacity. The influence of the chemical composition and the solidification conditions during LPBF on the microstructure evolution and the related microstructure-property-relationships of bulk and lattice structure specimens will be discussed.