Maraging steels are martensitic steels that are strengthened by the precipitation of nano-sized intermetallic phases and which are used for high-performance applications such as for aircraft parts, missile parts or in the sport industry. The strengthening effect of the precipitates can be severely influenced by the chemical composition, the process history, and the heat treatment parameters. The industrial steel grade that is used in this thesis is a candidate for a specific structural aircraft part. Furthermore, the goal is to manufacture these parts using recycled material. To ensure that the mechanical properties fulfill the requirements this thesis focuses on determining the influence of processing parameters and the chemical composition on the precipitation behavior, on the formation of austenite, and the mechanical properties of a Co-free maraging steel. To achieve this a combination of laboratory-processed model alloys and an industrially processed alloy with various heat treatment conditions were characterized using high-resolution methods. The microstructural changes were identified and correlated to the changes in strength, hardness, and toughness. Furthermore, a novel approach for determining the precipitation strengthening was developed and used to learn about the underlying strengthening mechanisms in ¿-Ni3Ti and ß-NiAl strengthened Co-free maraging steels. It was found that severe plastic deformation had a strong influence on the hardness and aging response, that the cooling rate can be used as a parameter to influence the precipitation hardening, and that the volume fraction of the η-Ni3Ti and the ß-NiAl precipitates is influenced by Cr, Mo and the Ti- and Al-concentration.