Development of novel austenitic and austenitic-ferritic advanced high strength steels for laser powder bed fusion
This study addresses the development of novel advanced high strength steels (AHSS) that take advantage of the processing conditions during additive manufacturing (AM) by laser powder bed fusion (L-PBF). The alloy screening was guided by computational thermodynamics and the usage of powder mixtures of X30Mn21 steel and Al. Increasing Al contents, ranging from 0 to 5.3 wt.%, pro-moted austenitic-ferritic solidification and allowed for tailoring the stacking fault energies (SFE). On the one hand, the transition from austenitic to ferritic-austenitic solidification allowed for controlling the microstructure and texture evolution during AM. On the other hand, the wide SFE range between 8 J/mm² (0 wt.% Al) and 44 J/mm² (5.4 wt.% Al) enabled 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 L-PBF and after plastic deformation was analyzed by XRD, SEM, EDX, EBSD and TEM. Mechanical properties of bulk specimens were analyzed by tensile testing for different tensile directions. The energy absorption capacity of specimens with lattice structures was analyzed by compression tests. The influence of the chemical composition and the solidification conditions during L-PBF on the microstructure and the related micro-structure-property-relationships of bulk and lattice structure specimens will be discussed.