Abstract: Precipitation of multiple strong nanoprecipitates is crucial for the development of ultrahigh-strength structural materials with a strength of 2.5 GPa or above. Nevertheless, the ductility usually loses rapidly with strength due to limited dislocation mobility and high cracking tendency if coarse non-deformable precipitates are employed. Herein, we report a 2.5 GPa maraging steel strengthened by an ultrahigh density of intermeshed shearable nanostructures consisting of Ni(Al, Fe) nanoprecipitates and Mo-rich (∼30 at.%) disordered clusters, both of which assume coherent interfaces. The fully coherent B2-Ni(Al, Fe) particles precipitate in an extremely fast fashion, effectively accelerating local aggregation of low-diffusivity Mo atoms and promoting the formation of Mo-rich clusters surrounding them. This elemental partition was found to be further enhanced by Co addition via depleting both residual Al and Mo within the matrix, leading to the formation of copious yet fine intermeshed nanostructures. During plastic deformation, the interlocked nanostructures not only enhance local cutting stress by combining long-range elastic and short-range chemically ordering effects but also improve dislocation activity and resist shear-induced plastic instability. The multiple shearable nanostructures endow decent ductility (> 6%) of the 2.5 GPa steel, suggesting a new paradigm for designing ultrastrong steels.

Key words: Ultrahigh strength steel, Co-precipitation, Deformable nanostructures, Mechanical properties, Nanoprecipitates