Strain hardening and heterogeneous deformation during twinning in Hadfield steel

We identify the role of deformation twinning and twin–twin intersections on the strain hardening behavior of Hadfield steel single crystals using strain field measurements. In situ and ex situ strain field measurements resolved at micrometer length scales are obtained using digital image correlation. Ex situ measurements reveal that macroscopic twin-bands, which are composed of a mixture of fine twin-lamella and matrix material, generate approximately 30% axial strain. This measurement is comparable to strain predictions based on twinning crystallography. In situ measurements reveal that primary and secondary twins may nucleate simultaneously, but the primary twin-system remains predominantly active with increased deformation. The intersection of primary and secondary twin-systems was directly linked to an increase in the strain hardening response.