Strain rate induced TRIP/TWIP effects and damage initiation in a novel Fe-Mn-Al-Nb medium manganese steel: Experiments and modeling

Abstract

To evaluate the strength and plasticity of Fe-Mn-Al-Nb medium manganese steel (MMnS) under extreme impact conditions, tensile tests were carried out using a universal testing machine and a split Hopkinson tensile bar, with strain rates ranging from 0.001 s⁻¹ to 3000 s⁻¹. The initial crystal orientation data provided by electron backscatter diffraction (EBSD) were used to establish a crystal plasticity phase-field (CP-PFM) model using DAMASK software, and the plasticity behavior and damage evolution of this model were studied. The study systematically examines the plastic deformation mechanisms of MMnS at strain rates of 0.001 s⁻¹ to 3000 s⁻¹, as well as damage initiation at the dynamic strain rate. The results show that strain hardening at 0.001 s⁻¹ is mainly determined by the transformation induced plasticity (TRIP) effect and dislocation activity. At the strain rate of 3000 s⁻¹, initial hardening results primarily from the combined actions of dislocations and the TRIP effect, while subsequent hardening is dominated by the TRIP and twinning induced plasticity (TWIP) effects. Dislocation accumulation leads to the formation of low-angle grain boundaries and promotes strain localization. In addition, austenite is capable of activating a greater number of slip systems compared to ferrite, enabling it to accommodate external forces via multiple slip pathways. This characteristic results in enhanced plasticity and deformation capacity for austenite. It is noted that damage nucleates initially at the interfaces between ferrite and austenite grains and then diffuses into the grains.