Pre-compression effects on strain-hardening behavior in Fe-15.5Mn-1.4Al-0.6C steel: Insights from TWIP effects and microstructural heterogeneity

This study investigates the effects of heterogeneous microstructures and twinning-induced plasticity (TWIP) effect on the strain-hardening behavior of high-Mn steel, aiming to enhance the understanding of mechanisms that can improve the yield strength of high-Mn steels. Using advanced ex-situ electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), we reveal the roles of bimodal grain structures, twin-interleaved structures, detwinning, and nucleation of new twins in enhancing the mechanical response under complex strain paths. Results indicate that large pre-compression enhances both yield strength and ultimate tensile strength while maintaining elongation and strain-hardening capacity. The pre-compression treatment enhances material strength through introducing dense dislocation networks, deformation twins (DTs), and grain refinement, while retaining ductility via new twin nucleation in coarse-grained (CG) regions. The synergistic effect between hetero-deformation-induced (HDI) hardening and local strain-hardening triggered by twin interactions significantly improves the strain-hardening capacity. However, the HDI hardening contribution progressively weakens during tensile deformation due to a reduction in hetero-interface density (caused by twin-refinement of coarse grains) and a diminishing dislocation density disparity between CG and fine-grained (FG) regions. These insights advance the fundamental principles governing high-Mn steel deformation, supporting the development of high-performance Fe-Mn-C-Al alloys for automotive applications. • Pre-compression strengthens steel via grain refinement and high-density dislocations • Strain path reversal activates new twin nucleation retaining ductility • HDI hardening and twin interaction-induced localized hardening • HDI hardening attenuates due to reduced hetero-interface density