Effect of strain rate on mechanical properties and microstructural evolution in a ferrite austenite duplex medium Mn steel

Abstract

Here, we explored the mechanical behavior and microstructural evolution of a ferrite-austenite duplex medium Mn steel under extremely high strain rate (10³ s^-1). It is found that the yield strength increases by 135 MPa with the increase of strain rate from 10^–3 to 10³ s^-1. Yet, the strain hardening rate decreases significantly, resulting in a lower ultimate tensile strength and a reduced uniform elongation. Microstructural analysis and thermodynamic calculations reveal that dislocation multiplication is promoted by high-strain-rate deformation at the small strain of 4.0 %. At large strains, adiabatic heating causes a substantial temperature increase, reaching 367 K at the engineering strain of 25.9 %. This temperature rise leads to a significant increase in the stacking fault energy of austenite, suppressing transformation-induced plasticity effect. The elevated temperature also enhances dynamic recovery of dislocations, inhibiting dislocation multiplication during high-strain-rate deformation. As a result, the suppressions of both transform-induced plasticity effect and dislocation multiplication result in the decrease of strain hardening rate.