Ultrahigh strain-rate dynamic recrystallization in high manganese austenitic steels: Mechanisms of shear band anisotropy and resistance to localized failure

Abstract

This study addresses the critical challenge of catastrophic shear failure in deep underground support materials under ultrahigh strain-rate loading (∼10⁴ s⁻¹) characteristic of severe rockburst events. We investigate the compression response and plastic instability mechanisms of a novel high manganese austenitic steel (HMAS) specifically engineered for impact-resistant applications through integrated dynamic experimentation and multiscale characterization. Utilizing a miniature split-Hopkinson pressure bar system, we reveal that HMAS achieves exceptional mechanical performance at 2 × 10⁴ s⁻¹, demonstrating a remarkable compressive strength of 2.5 GPa coupled with 45 % fracture strain, and notable strain rate sensitivity. These outstanding mechanical properties are attributed to multiple deformation mechanisms, including twinning-induced plasticity (TWIP), distorted stacking faults (SFs), nanoscale body-centered cubic (BCC) phase transformations, and the formation of adiabatic shear bands (ASBs) at extreme strain rates. Our analysis reveals that dynamic failure in HMAS primarily occurs along the XY and YZ planes, with cracks propagating along the maximum shear stress direction within ASBs. Microstructural examination via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) confirms extensive dynamic recrystallization (DRX) within ASBs. This DRX process refines grain structure and mitigates further strain concentration, thereby delaying catastrophic failure despite prior shear localization. Texture analysis reveals that distinct crystallographic orientations between the XY and YZ planes (e.g., dominant Brass/Goss textures in XY vs. Rotated Goss/Y textures in YZ) promote anisotropic ASB formation. These orientation differences alter the Schmid factor distribution for primary slip systems ({111} < 110 > ), favoring shear localization along specific planes. These findings provide a mechanistic understanding of HMAS’s strain rate-dependent strengthening and failure behavior, offering valuable insights into its potential for mitigating rockburst-induced dynamic loads in deep underground engineering applications.