Some precipitation hardened steels use a combination of the intermetallic -NiAl and -Ni3Ti phases to achieve a beneficial combination of ultra-high strength and toughness. The age-hardening in such steels is a complex process that includes the simultaneous formation of precipitates and reverted austenite. The phase constitution and volume fraction of the precipitates strongly depends on the content of the alloying elements, such as Ti, Al, Cr and Mo. By using a step-wise alloy design scheme and high-resolution characterization methods this study seeks to reveal the influence of Ti and Al variations as well as of Cr and Mo on the precipitation hardening and austenite reversion for Co-free maraging steels based on the Fe-12Ni alloy system. It was found that Cr plays a major role in promoting the precipitation of the -Ni3Ti phase and simultaneously increases strength and toughness, Ti and Al variations can change the balance between -Ni3Ti and -NiAl precipitates and Mo significantly promotes austenite reversion.