Copious intragranular B2 nanoprecipitation mediated high strength and large ductility in a fully recrystallized ultralight steel

High-strength Fe-Mn-Al-C-Ni low-density steels are highly desirable in lightweight transportation, safe infrastructure, and advanced energy applications. However, these steels generally suffer from limited ductility owing to the formation of coarse B2 particles at grain boundaries. In this study, we proposed a strategy to introduce copious intragranular B2 nanoprecipitates within fully-recrystallized fine austenitic grains in a Fe-26Mn-11Al-0.9C-5Ni ultralight steel by a simple cold rolling and annealing process. Compared with steel where B2 particles are mainly distributed at grain boundaries, the yield strength and ultimate tensile strength of this steel increased from 768 MPa and 1100 MPa to 954 MPa and 1337 MPa, respectively, whereas the total elongation increased from 38% to 50%. The higher yield strength was primarily due to the synergistic strengthening effect of intragranular B2 nanoprecipitates and grain refinement. The excellent ductility and sustained work hardening were mainly attributed to the strong dislocation storage capability mediated by the intragranular B2 nanoprecipitates and the greater dynamic slip band refinement strengthening effect. Hence, the achievement of copious intragranular B2 nanoprecipitation in fully recrystallized ultralight steel offers an effective pathway for developing lightweight materials with high strength and large ductility.