Modeling the austenite to ferrite phase transformation for steel development

In the so-called ”Advanced high strength steels” tailored microstructures are applied combining different constituents with different mechanical properties. All these steels have to undergo the proeutectoid ferrite precipitation. In order to better understand and control this precipitation it is necessary to investigate the influence of substitutional alloying elements on this precipitation and the local element partitioning behavior. Here, physical models were applied that are based on a diffusion-controlled approach and on the multicomponent multi-phase-field method and are realized in the packages DICTRA and MICRESS. It could be shown, that the substitutional alloying elements and especially the austenite former manganese lead to a two-step precipitation process of ferrite. At technical relevant times this process is controlled by carbon diffusion. The diffusion of the substitutional elements only starts at longer transformation times. Additionally, the influence of the proeutectoid ferrite precipitation on a subsequent transformation of retained austenite to martensite was investigated, as well as multi-dimensional microstructure development and, by transferring the structure to a finite element mesh, its mechanical properties.