The determining role of the recrystallization degree and average size on the mechanical response of high manganese steel

High manganese steel with heterogeneous structures was developed through asymmetrical rolling and annealing to achieve superior mechanical performance for cryogenic applications. By adjusting the annealing temperature (850 °C, 800 °C, 750 °C), the recrystallization fraction and grain size were controlled, influencing the mechanical properties and deformation mechanism at room temperature (RT) and liquid nitrogen temperature (LNT). Results show that higher annealing temperatures reduce strength but enhance ductility at both RT and LNT. Notably, the CR-850 specimen exhibits the highest product of strength and elongation (PSE) of 78.3 GPa·%, with tensile strength of 1530 MPa and elongation of ∼50 % at LNT. This exceptional performance is attributed to grain boundary and dislocation strengthening. The superior ductility benefits from ⅰ) larger average grain size and higher recrystallization degree, ⅱ) the notable twinning induced plasticity effect (TWIP) and strong back stress from strain distribution between grains; ⅲ) minimal HCP phase formation, preventing premature fracture due to deformation incompatibility. The transformation induced plasticity (TRIP) effect was observed during LNT deformation. However, the CR-750 specimen, with the highest HCP content, experiences reduced ductility due to increased stress and incompatibility between the HCP phase and FCC matrix. While the HCP phase contributes to the TRIP effect, excessive formation negatively impacts plasticity during further deformation.