Steel, as the cornerstone of modern civilization and industry, plays a critical role in the performance evolution of extreme load-bearing components, with yield strength becoming a core design parameter for service safety. After nearly a century of development, the yield strength of ultra-high-strength aerospace alloys has reached approximately 2 GPa. However, the development of next-generation frontier technologies such as drive shafts for deep-space exploration vehicles urgently demands a major leap to achieve an ultra-high yield strength of 3 GPa. This requires materials to attain ultra-high strength without compromising key damage tolerance indicators such as total elongation, reduction of area, and fatigue resistance.

The core challenge in approaching 3 GPa strength lies in the catastrophic loss of toughness that accompanies ultra-high strength. Conventional single-mechanism strengthening approaches such as cold work hardening tend to induce localized stress concentrations, causing total elongation to plummet to below 3% and triggering brittle cleavage fracture. Whether it is embrittlement caused by brittle intermetallic phases in aged maraging steels or the accumulation of dislocations in cold-drawn wires, premature crack initiation is a common outcome. How to overcome the traditional strength-ductility trade-off while ensuring compositional homogeneity and suppressing harmful grain boundary segregation, and achieve industrial-scale production of 3 GPa-grade high-toughness steel, remains a major bottleneck in the field of materials science.

To address the above challenges, a team comprising researchers from Beihang University, Central Iron and Steel Research Institute, and other institutions conducted a systematic study using ZEPTOOLS' in situ SEM system. The team innovatively combined tailored nanoprecipitate design with high-temperature severe plastic deformation. By synergistically constructing a hierarchical microstructure incorporating multiple misfitting nanoscale precipitates, a high density of spatially uniformly distributed dislocations, and ultra-fine equiaxed grains, they successfully achieved the preparation of ultra-high-strength steel with a yield strength of 3 GPa while maintaining excellent damage tolerance and industrial scalability.

Title: Ductile and scalable 3 GPa steel via a hierarchical microstructural architecture
Journal: Nature Communications
Link:https://doi.org/10.1038/s41467-026-74216-4

This study systematically addresses the pervasive strength-ductility trade-off in ultra-high-strength steels by elaborating a novel maraging steel preparation strategy based on hierarchical microstructural architecture design, with a nominal composition of Fe-16Ni-7Mo-1.6Ti-15Co-0.1Al (wt.%). To overcome the conventional technical bottleneck of catastrophic ductility loss and brittle fracture when yield strength approaches 3 GPa, the research team implemented deep synergistic regulation between the tailored chemical composition and an innovative high-temperature severe plastic deformation process. By setting the soaking temperature at 950 °C, controlling the final forging temperature above 800 °C, and achieving a cumulative true strain of 10 or greater, the process introduced an ultra-high density of dislocations and an ultra-fine grained precursor state at the microscale. This innovative thermomechanical processing path not only effectively avoided harmful solute segregation at grain boundaries and premature precipitation of brittle intermetallic compounds, but also laid a solid foundation for subsequent large-scale uniform aging strengthening, demonstrating high industrial application feasibility.

This research delves into how to precisely orchestrate internal defects in materials at the micro- and nanoscale to overcome the problem of premature cracking in conventional high-strength steels caused by stress concentration from single-mechanism strengthening. Through synergistic regulation, the martensitic matrix evolves after aging into an ultra-fine and isotropic hierarchical structure with an average equiaxed effective grain size of only 0.53 μm and a high-angle grain boundary fraction of up to 79.6%. Meanwhile, the matrix retains a high dislocation density of up to 1.05 × 10^16 m⁻², which forms a spatially well-distributed network rather than the localized tangles or dislocation wall structures commonly seen in conventional cold-rolling processes, thereby ensuring sustained strain-hardening capability under ultra-high stresses. On this basis, two types of nanoscale co-precipitates with different lattice misfits—namely spherical ω-phase and needle-like η-Ni₃Ti phase—are dispersed throughout the matrix with ultra-high number densities and ultra-fine nanoscale radii. These not only effectively hinder dislocation slip under high-stress conditions but also serve as extensive sources for dislocation nucleation, thereby effectively delaying the onset of localized plastic instability.

To elucidate the dynamic plastic deformation and fracture evolution mechanisms of this material at the microscale, the study specifically designed and conducted dynamic in situ SEM tensile tests. During this process, the research team utilized an in situ high-temperature tensile stage developed by ZEPTOOLS to perform real-time micromechanical loading observations on sheet specimens with a thickness of 0.5 mm and width of 1.5 mm at a constant deformation rate of 2 μm/s. Through this high-precision in situ characterization approach, the study clearly captured the critical role of the hierarchical microstructure during crack propagation, directly confirming that this design fundamentally transforms the mixed-mode brittle cleavage fracture observed in the conventional cold-rolled and aged state into a microvoid-coalescence-dominated ductile fracture behavior. Thanks to the precise loading and observation enabled by this instrument, the study demonstrated that the spatially uniformly distributed high-density dislocations and nanoscale co-precipitates induce crucial stress relaxation at crack tips, while the high-density high-angle grain boundaries of the ultra-fine equiaxed grains force the crack propagation path to exhibit severe tortuosity and serration, thereby significantly amplifying energy dissipation during microvoid growth. This successfully reveals the intrinsic fracture mechanics essence underlying the material's high toughness at the 3 GPa ultimate strength level.

The precise precipitate design and microstructural宏观调控 (macro-control) strategy constructed in this study ultimately delivered a series of outstanding performance metrics that break existing international records in macroscopic mechanical behavior. Room-temperature tensile tests demonstrated that the new steel achieved a yield strength of up to 2977 MPa and a tensile strength of 3009.5 MPa, while maintaining a total elongation of 7.0% and a reduction of area as high as 47.5%, far surpassing all existing 3 GPa-grade counterparts. In terms of damage tolerance, the steel exhibited a plane-strain fracture toughness of 26.0 MPa·m^1/2 and a room-temperature high-cycle fatigue limit strength of up to 1240 MPa measured at 10^7 cycles. Even more groundbreaking is that under the extreme high-temperature environment of 500 °C, the material still maintained an ultra-high yield strength exceeding 2 GPa with good ductility. Moreover, these excellent comprehensive mechanical properties are not limited to laboratory-scale preparation; they have been fully and stably reproduced in industrial-scale large-diameter bars of 30 mm diameter and over 1 m in length, fully confirming the significant potential of this technology for large-scale industrial applications in the manufacturing of extreme-load-bearing components for aerospace and other industries.

The ZEPTOOLS PicoFemto in situ SEM high-temperature tensile stage is an advanced device integrating mechanical tensile loading and high-temperature environmental modules, capable of performing tensile experiments while simultaneously heating the sample within the SEM. This product employs a next-generation high-temperature tensile solution, where the heating stage directly contacts the sample, ensuring temperature accuracy and stability.