Effects of Powder Atomization Route and Post-Processing Thermal Treatments on the Mechanical Properties and Fatigue Resistance of Additively Manufactured 18Ni300 Maraging Steel

In this work the effect of microstructural homogenization and solution annealing prior to ageing on mechanical properties and fatigue resistance of 18Ni300 maraging steel parts processed by laser powder bed fusion (L-PBF), using two different feedstock powders with different N and O contents is investigated. The static mechanical properties are not significantly affected by the selection of the different feedstock powders. This is ascribed to the extremely fine size of the nonmetallic inclusions, characteristic of L-PBF process, even by using feedstock powders containing higher O and N contents. The tensile properties in both “directly aged,” and “homogenized, solution annealed and aged” samples are comparable. The tensile strength and ductility are slightly improved compared with the vacuum melted wrought counterparts. The dynamic mechanical properties are affected by the O and N contents of the powders. Heat treatment schedule imposed a significant effect on the fatigue properties. The obtained fatigue strength in directly aged samples is already comparable to the wrought counterparts. Fatigue resistance is improved by using feedstock powders with lower oxygen and nitrogen levels. Proper homogenization heat treatments prior to ageing led to a further improvement of fatigue strength because of the elimination of intercellular microsegregation.