Effects of Strain Rate on the Deformation Mechanism of Ultra-high Strength TWIP Steel

Abstract

The deformation mechanism of Fe-20Mn-0.6C twinning-induced plasticity (TWIP) steel was studied with respect to different strain rates ranging from 10⁻⁴ to 10³ s⁻¹. Moreover, the microstructure of the ultra-high strength TWIP steel at each strain rate was characterized by transmission electron microscopy (TEM). The TWIP steel exhibits three distinct strain hardening stages with increasing true strain. In stage II, dσ/dε shows a plateau at the strain rates of 10⁻³ to 10⁻¹ s⁻¹, while dσ/dε continuously decreases in the other stages with increasing strain rate. The deformation mechanism of TWIP steel under the high strain rate was a process in which the deformation twin and the dislocation slip promoted and restricted each other. When the strain rate is higher than 10² s⁻¹, the increase in the adiabatic heating temperature (approximately 143°C) suppresses the secondary twinning and enhances the softening effect.