Enhancing strength and plasticity by tailoring microstructure heterogeneity in FeMnCoCrNbC high-entropy steel

Heterostructures were developed in FeMnCoCrNbC high-entropy steel (HES) by tailoring the annealing temperature and time. The dispersed nano-precipitates of NbC exert a pronounced pinning effect on grain boundary migration, thereby effectively retarding recrystallization. This enables the formation of heterogeneous HES with partial recrystallization and homogeneous HES with full recrystallization. Notably, the heterogeneous HES with a recrystallization fraction of 69.3 % exhibits outstanding strength–ductility synergy, with a tensile strength above 1 GPa, a yield strength of 825 MPa, and a strength–ductility product (SDP) of 44 GPa∙%. Beyond precipitation strengthening and TRIP/TWIP effects, the hetero-deformation induced (HDI) strengthening and HDI work hardening associated with the heterogeneous structure further enhancing the yield strength and ductility. The integration of microstructural heterogeneity with conventional strengthening mechanisms thus provides an effective pathway to achieve simultaneous improvement of strength and ductility in HESs.