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 fer rous alloys. The transformation proceeds through the: formation of suc cessive variants of the product phase within a unit cell representativ e of a grain: interactions between neighbouring grains are simulated b y the choice of periodic boundary conditions. From a thermodynamical a nalysis, 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-dimension al finite element simulation of the transformation, considering an ela stoplastic 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 infl uence of both external load and internal stresses built during the pre press of the transformation. These are related to global evolutions of transformation plasticity vs, transformation progress. Comparison wit h experiments show a similar form of the evolutions of the total strai n; however. the model overestimates the strain levels. The possible re asons for this discrepancy are discussed. (C) 1998 Elsevier Science Lt d.