Achieving strength-ductility synergy via dissolution-reprecipitation of B2 intermetallic compounds in austenitic lightweight steel

Strength-ductility synergy in Fe-Mn-Al-C-Ni austenitic lightweight steels is governed by recrystallization-mediated B2 precipitation. Unlike conventional approaches that primarily depended on annealing temperature or time to control grain size, morphology and distribution of B2 phase. Herein, a “dissolution-reprecipitation” strategy employing high-temperature annealing (1150 °C), 5% cold rolling, and two-step ageing is designed to achieve a uniform dispersion of intragranular B2 particles (86 nm) and κ′-carbides (5 nm) within a completely recrystallized austenitic matrix (2.2 μm). Higher annealing temperature dissolves the coarse intergranular B2 phase, enabling elemental homogenization during annealing process. While cold rolling deformation introduces controlled dislocations, assisting the heterogeneous nucleation of intragranular B2 phase during subsequent ageing process. The synergistic mechanisms of dissolution-driven elemental homogenization and dislocation-assisted nucleation are essential for achieving uniform distribution of intragranular B2 particles. The resultant dual precipitations contribute a 260 MPa hardening increment and promote sustained work hardening via planar slip and Orowan bypassing, achieving an exceptional strength-ductility synergy. Our findings provide an effective pathway to control recrystallization-mediated B2 precipitation and insights into the development of austenitic lightweight steels.