In the present work, novel alloy concepts of low-density, intermetallic-strengthened high-Al alloyed steels are developed primarily to investigate the microstructure evolution and the formation of intermetallic phases. The designed model alloys aim at the concurrent precipitation of diverse intermetallic phases and are based on novel concepts to control intermetallic precipitation. A solubilityassisted precipitationconcept is developed and successfully validated, which uses the favorable elemental partitioning between the matrix phases of a duplex alloy to precipitate intermetallic phases phasespecifically. The microstructural evolution of these alloys is affected by the presence of intermetallic phases and demonstrates a high complexity with the emergence of new phases during processing and isothermal aging. Phase transformations involving the intermetallic phase formation are studied by in-situ heating experiments and synchrotron X-ray diffraction as well as transmission electron microscopy and atom probe tomography. A novel phase transformation is proposed for the intermetallic Fe3AlC-phase with the formation of an ordered precursor followed by its phase decomposition into a disordered matrix phase and chemically altered ordered Fe3AlC-phase. The room temperature mechanical properties of the high-Al alloyed intermetallic-strengthened steels exhibit high yield strengths in exceedance of 1 GPa. Considering their low density, the alloy systems demonstrate exceptional density-specific mechanical properties.