Abstract: In this work, we proposed a novel Cu/θ dual nanoparticles strategy to tailor the austenite characteristics of a medium Mn steel via a tempering-annealing process to optimize the mechanical properties. We explored the effects of Cu-rich particles and cementite precipitated in the tempering process on the austenite reversion during the subsequent annealing process. Both experiments and numerical simulations verified that the austenite inherited from cementite had a finer size and a higher Mn enrichment compared with the austenite originating from the tempered martensite matrix. In addition, quantitative evaluations revealed that the pinning effect exerted by the Cu-rich particles could significantly hinder the α/γ interface migration and the recrystallized grain growth, thereby further refining the final microstructure. With contributions from the effects of dual nanoprecipitates on the austenite reversion, the heterogeneous austenite grains inherited from varying nucleation sites ensured the sustained and gradual deformation-induced martensite and twinning formation. Therefore, the Cu-added steels subjected to a tempering-annealing process achieved synergetic enhancement of the tensile strength from 1055 MPa to 1250 MPa and elongation from 33% to 45%. This strategy may provide new guidance for the development and alloy design of high-performance medium Mn steels.

Key words: Dual nanoparticles, Medium Mn steel, Tempering-annealing process, Austenite reversion, Mechanical properties