Abstract
The presented research was aimed at applying laser powder bed fusion (LPBF) technology and TRIP (Transformation Induced Plasticity) steel with medium Mn content to produce thin-walled parts with enhanced crashworthiness. It was expected that the simultaneous use of the excellent combination of strength and ductility of the new type of medium-Mn steel and the advantages of LPBF technology would allow the development of an alternative to the conventional method of manufacturing the energy absorbing components. The energy absorption capability of LPBF-processed Fe-0.15C-7.5Mn-1.8Al steel was evaluated based on its deformation behavior under monotonic and impact loading. Tensile and Charpy V-notch specimens were fabricated by LPBF with layer thicknesses of 30 and 60 μm, using processing windows set established according to the criteria of low porosity (<0.3%) and good surface quality. Specimens were tested in as-built state and after intercritical annealing at a constant temperature (670 °C), but for different holding times and cooling rates to obtain a large fraction (30–50 vol%) of retained austenite capable of strain-induced martensitic transformation. Based on multiscale microstructure examinations (OM, SEM, EBSD, XRD, EDS) the relationships between the morphology of LPBF-specific microstructures before and after intercritical annealing, as well as between their behavior in tensile and impact test, were analyzed and discussed. For both layer thicknesses, the best combination of strength, elongation and impact toughness was obtained after annealing at 670 °C for 6 h followed by argon cooling. LPBF technology has been shown to be suitable for the fabrication of thin-walled energy-absorbing components from medium-manganese TRIP steel with the potential to reduce fabrication time by doubling the layer thickness compared to standard.
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