Ultra-high strength maraging stainless steels are widely used in many critical applications, such as aircraft landing gears owing to their excellent strength and good processability. However, traditional ultra-high strength maraging stainless steels face the challenge of balancing strength and ductility in the pursuit of ultra-high strength. This is mainly due to the semi-coherent or non-coherent relationship between the precipitated nanoparticles and the body-centered cubic (BCC) martensitic matrix. In this study, we design a novel ultra-high strength maraging stainless steel (Fe-7.95Cr-13.47Ni-3.10Al-1.83Mo-0.03C-0.23Nb, wt.%) using a cluster formula approach. Alloy ingots are prepared by vacuum induction melting under an argon atmosphere, followed by hot rolling at 950℃ and multiple passes of cold rolling. Finally, the alloy is aged at 500℃ for up to 288 h. Microstructural characterizations of the alloy in different aging states are performed using EBSD and TEM. As a result, the martensitic structure of the alloy was fragmented and elongated, with high-density dislocations (~ 1.8×10-3 nm-2) and a large number of coherent B2-NiAl nanoparticles (< 5 nm) observed in the BCC martensitic matrix after cold rolling and aging. In terms of mechanical properties, the alloy exhibits significant age-hardening, with a peak-aged hardness of 651 HV after ageing treatment. It also demonstrates an extraordinarily high yield strength (sYS = 2.3 GPa) and a decent elongation (El = 3.6%), indicating a well-balanced strength-ductility property. Finally, we present an in-depth discussion on the origins of the ultra-high strength in the novel alloy, revealing that various microstructural features contribute to its strengthening mechanism. This study provides valuable guidance for the design of high-performance ultra-high strength maraging stainless steels.
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