Strain Hardening Associated with Dislocation, Deformation Twinning, and Dynamic Strain Aging in Fe–20Mn–1.3C–(3Cu) TWIP Steels

Abstract

The effects of Cu on stacking fault energy, dislocation slip, mechanical twinning, and strain hardening in Fe–20Mn–1.3C twinning-induced plasticity (TWIP) steels were systematically investigated. The stacking fault energy was raised with an average slope of 2 mJ/m2 per 1 wt% Cu. The Fe–20Mn–1.3C–3Cu steel exhibited superior tensile properties, with the ultimate tensile strength reached at 2.27 GPa and elongation up to 96.9% owing to the high strain hardening that occurred. To examine the mechanism of this high strain hardening, dislocation density determination by XRD was calculated. The dislocation density increased with the increasing strain, and the addition of Cu resulted in a decrease in the dislocation density. A comparison of the strain-hardening behavior of Fe–20Mn–1.3C and Fe–20Mn–1.3C–3Cu TWIP steels was made in terms of modified Crussard–Jaoul (C–J) analysis and microstructural observations. Especially at low strains, the contributions of all the relevant deformation mechanisms—slip, twinning, and dynamic strain aging—were quantitatively evaluated. The analysis revealed that the dislocation storage was the leading factor to the increase of the strain hardening, while dynamic strain aging was a minor contributor to strain hardening. Twinning, which interacted with the matrix, acted as an effective barrier to dislocation motion.