Maraging steels are high-strength steels known for their good combination of strength and toughness. Due to their well-balanced mechanical properties they are used in the fields of aviation, ship building, tool making and in the chemical industry. Solution annealing is an essential part of the heat treatment cycle for maraging steels. It is crucial for the targeted development of the microstructure and the mechanical properties. The aim of this work was to investigate the influence of the solution annealing temperature on the microstructure of two Fe-12Ni maraging stells and to model the strength based on the microstructure. Electron backscatter diffraction, X-ray diffraction and atom probe tomography were used to characterise the microstructure. The mechanical properties were determined by hardness testing. A higher solution annealing temperature leads to an increase in the number density and volume fraction of NiAl precipitates with a simultaneous decrease in Ni\textsubscript{3}Ti precipitates. Fe-12Ni maraging steels appear to be robust in terms of hardness and strength to variations in the solution annealing temperature.