The Effect of Twinning and Slip on the Bauschinger Effect of Hadfield Steel Single Crystals

The Bauschinger effect (BE) in single crystals of Hadfield manganese steel (Fe, 12.3Mn, 1.0C in wt pct) was studied for three crystallographic orientations, [111], [123], and [001]. Both forward tensionreverse compression (FT/RC) and forward compression-reverse tension (FC/RT) loading schemes were used to investigate the role of deformation history on the BE. The evolution of stress-strain response and a dimensionless Bauschinger parameter were used to study the BE. The BE stems from long-range back stress generated by the dislocation pileups at the twin and localized slip boundaries. Twinning boundaries present a strong obstacle and lead to a strong BE. If localized slip followed twinning, permanent softening was evident, such as in the case of the [111] FT/RC scheme. Localized slip and multiple slip in the forward loading provided a transient effect in the stress-strain response without a significant permanent softening. Hadfield steel single crystals have demonstrated a high BE for orientations conducive to combined twinning/slip deformation. The BE increased with increasing prestrain, then saturated and started to decrease, in contrast with precipitation-hardened alloys. A unique strain-hardening approach along with the back stress calculation was introduced into a viscoplastic selfconsistent (VPSC) formulation. The strain-hardening formulation incorporates length scales associated with spacing between twin lamellae. The simulations correctly predicted the BE and the stress-strain response for both forward and reverse loading.