A microstructural investigation of adiabatic shear bands in an interstitial free steel

We report the microstructural characterization of induced adiabatic shear bands (ASB) in a hot-rolled interstitial free (IF) steel deformed at high strain rates (>2.8 × 104 s−1) in a split Hopkinson bar under controlled conditions at −50 and 25 °C. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) were used to reveal the degree of subdivision within ASB and neighboring grains. Deformation twins were found in adjacent grains suggesting that twinning occurs before the flow associated to shear banding. Progressive subgrain misorientation (PriSM) recrystallization is a plausible mechanism to explain the development of a new structure consisting of weakly textured ultrafine grains (0.1-0.5 μm) within the ASB. Recrystallization is proposed to occur by the formation and mechanical rotation of subgrains during deformation, coupled with boundary refinement via diffusion during shear band cooling. The presence of elongated subgrains and grains perfectly aligned within regions resembling a former lamellar structure within bands supports the occurrence of such a mechanism.