Metal Additive Manufacturing Conference - MAMC 2021

Carbon-containing ferrous alloys with >0.2 wt.% carbon are considered difficult to weld materials and are thus expected to have poor processability when using Laser Powder Bed Fusion (L-PBF). This is connected to the high cooling rates of L-PBF that result in the formation of martensite and internal residual stresses that create a significant risk of cold cracking within the material. However, the characteristics of martensite formation, its substructure and its properties in L-PBF produced ferrous alloys is a subject that remains poorly understood. Presented work summarizes the effect of carbon on the formation and properties of martensite over a range of model Fe-C alloys as well as low-alloy steels, with a specific focus on martensite properties and its effect on L-PBF processability. This was done using a combination of hardness measurements, optical and scanning electron microscopy, transmission electron microscopy and atom probe tomography, that helped analyze the substructure, carbon distribution and precipitation within L-PBF produced martensite. Results indicate that ferrous alloys with up to 0.75 wt.% carbon can be produced defect-free by tailoring the laser scan strategy and build plate preheating to enhance the intrinsic heat treatment that takes place during processing.