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Highlights • The austenite-based, duplex and triplex structures were developed. • Different types of intra-granular and grain boundaries κ -carbides were observed. • The microstructure-dependent mechanical responses were analyzed. • This work can be used to tailor phase constituents of medium-Mn lightweight steels. Abstract We elucidate three distinguished microstructural features and their contribution to the overall properties and strengthening in a Fe–11Mn–10Al–1.25C alloy treated at various temperatures. At 1000 °C, the nano-scaled ordered κ -carbides in the austenitic matrix contributed to YS (1041 MPa) without scarifying ductility (∼30%). At 900 °C, the significantly refined triplex microstructure with GB κ -carbides caused similar YS but limited ductility (∼8%). At 800 °C, a jump of YS but almost no ductility resulted from the synergic effects of the hard ferrite and lamellar microstructure. The microstructure-dependent mechanical responses were further clarified by analyses of flow curves and fractographs. [ABSTRACT FROM AUTHOR]

The present work aims to reveal the influence of κ-carbides precipitated in grain interior (GI) and along grain boundaries (GBs) with various characteristics on the strain hardening behavior of Fe–11Mn-(7, 10)Al-(0.6, 0.9, 1.2)C steels. Because of the higher probability for moving dislocations meeting with κ-carbides and shearing them, the increase in the volume fraction of shearable nano κ-carbides is more favorable for the improvement of the yield strength (YS) but thus induces the lower strain hardening rate (SHR), especially at low strains. The SHR maintains almost constant values even gradually increases during straining as the enhanced κ-carbide precipitation is beneficial to the planar glide softening and thus promotes the slip bands refinement. EBSD and TEM analysis reveal that both the unshearable coarse and sub-micron κ-carbides formed along GBs and in GI hinder the dislocation movement, and the former results in the significant strain localization in α/κ interfaces, consequently bringing about high SHR but premature failure. It is hoped that these findings will help achieving better synergy of strength and ductility of lightweight steels by utilization of the unshearable sub-micron κ-carbide in addition to the shearable one and partial-recrystallization. [ABSTRACT FROM AUTHOR]

In the present work, the Fe-13Mn-8Al-(0.7, 1.2)C steels were subjected to different post-cold rolling annealing treatments in a temperature range of 800–1000 °C for 15 min to investigate the microstructural evolution and the mechanical properties. Both steels annealed at 800 °C consisted of fine austenite and ferrite grains along with intergranular κ-carbides formed by eutectoid reaction, which contributed to the high strength but deteriorated ductility. With annealing temperature increasing, the volume fraction of ferrite and intergranular κ-carbides progressively decreased. Meanwhile, the precipitation of intragranular κ′-carbides enhanced the yield strength, whereas coarse austenite was harmful to both strength and elongation. The increase in C content increased the volume fraction of intergranular κ-carbides and austenite as well as retarded the austenite recrystallization, which further increased strength and strain hardening rate but deteriorate ductility. The deformation mechanism in austenite was massive planar slip. The microbands were widely observed in both steels at an annealing temperature above 900 °C. [ABSTRACT FROM AUTHOR]