Mechanical performance and deformation mechanisms of ultrastrong yield strength Fe-Cr-Ni-Mn-N austenitic stainless steel at 4.2 Kelvin

We report the mechanical performance and microstructural characteristics of a Fe-Cr-Ni-Mn-N alloy at cryogenic temperatures. The exceptionally high yield strength of 1.5 GPa combined with a high strain-hardening rate and no deterioration in ductility at 4.2 K was displayed. The evolution of deformation microstructure was examined using electron backscatter diffraction (EBSD), the transmission Kikuchi diffraction (TKD), high-resolution transmission electron microscopy (HRTEM), and aberration-corrected scanning TEM (STEM). The deformation microstructure mainly consisted of dislocation slip with L-C locks, {111} stacking fault formation, {111} deformation nanotwinning, and FCC → HCP shear transformation at 4.2 K. The occurrence of FCC-HCP shear transformation inside/near {111} twins to form γ- γtw -ε dual-phase structure induces a dynamic Hall-Petch effect that promotes the strain-hardening rate and enhances the strength-ductility combination. We believe that this alloy displays outstanding damage tolerance through a progressive synergy of deformation mechanisms leading to exceptional strength which provides a new insight into the commercialized development of high-performance alloys for cryogenic applications.