A micromechanical model of the martensitic transformation

A micromechanical model of the martensitic transformation at the grain scale has been established, considering the more specific case of ferrous alloys. The transformation proceeds through the: formation of successive variants of the product phase within a unit cell representative of a grain: interactions between neighbouring grains are simulated by the choice of periodic boundary conditions. From a thermodynamical analysis, a selection rule for the order and orientation of the forming martensitic variants has been established, based on internal stresses anisotropy. These concepts have been implemented into a two-dimensional finite element simulation of the transformation, considering an elastoplastic behaviour of both parent and product phases. Morphological and crystallographical features of the transformation are considered: one variant consists of a thin layer of elements within the mesh that can form with four possible discrete orientations. Simulation results show the development of the plate pattern as a combination of the influence of both external load and internal stresses built during the prepress of the transformation. These are related to global evolutions of transformation plasticity vs, transformation progress. Comparison with experiments show a similar form of the evolutions of the total strain; however. the model overestimates the strain levels. The possible reasons for this discrepancy are discussed. (C) 1998 Elsevier Science Ltd.