Place: Materials Research Society (MRS) Fall Meeting 2010, Boston, USA
Micromechanical modeling of deformation and failure of multiphase materials requires the mechanical properties of all individual phases and their interfaces to be known. If furthermore the microstructural evolution during deformation is to be described, phase transformations, grain growth, and recrystallization need to be modeled as well. In this work, an approach is described to develop representative volume elements (RVE) of multiphase steels containing multiple grains of ferrite, austenite, and martensite. In the work presented here, only plastic deformation shall be considered, while models for microstructural changes and crack initiation are only touched in the sense of an outlook. Plasticity in the ferrite and austenite grains of the RVE is described on the basis of crystal plasticity models. While such models have been demonstrated to yield reliable results for the plastic deformation of face centered cubic (fcc) metals, it is known that body centered cubic phases (bcc), like ferrite, exhibit a pronounced non-Schmid behavior and a large difference in the mobilities of edge and screw dislocations. Furthermore, the mobility of screw dislocations depends on orthogonal components of the local shear stress that do not contribute to the Peach-Koehler force on these dislocations. This dependence is assessed with atomistic simulations with semi-empirical potentials. Together with experimental and numerical results from the literature this yields a new atomistically informed constitutive relation for the deformation of ferrite grains. Hence, it is demonstrated that atomistic methods support the constitutive modeling by providing quantities and relations that are difficult, if not impossible, to measure directly with experimental methods.