Work-hardening/softening behaviour of B.C.C. polycrystals during changing strain paths: II. TEM observations of dislocation sheets in an if steel during two-stage strain paths and their representation in terms of dislocation densities
The relationship between the developed intragranular microstructure and the deformation history of a grain in a low-carbon IF steel is comprehensively investigated during monotonic deformation and two-stage strain paths. TEM micrographs show that dislocation sheets are currently generated parallel to the active slip planes. In the extended Taylor model developed in Part 1 of this paper, such substructural features are modelled and updated dynamically for each strain increment. The actual structure bears some memory of the deformation history. This paper shows the capability of the extended Taylor model to reproduce several features of the substructural developments observed in transmission electron micrographs after monotonic deformation and two-stage strain paths. The evolution of the mesostructural features in stable and unstable crystals are discussed in the context of the work-hardening/softening behaviour of the TF steel. It is demonstrated that the model can be used to predict qualitatively the intensity and the polarity of the dislocation sheets in a grain during any deformation path. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.