Analysis of banded microstructures in multiphase steels assisted by transformation-induced plasticity

The influence of the spatial distribution of the austenitic phase on the effective mechanical properties of a multiphase steel assisted by transformation-induced plasticity is analyzed using a numerical homogenization scheme. Representative three-dimensional volume elements with distinct microstructures are created applying a newly-developed algorithm based on the generation of a multilevel Voronoi tessellation; this approach allows for straightforwardly incorporating grains with complex, non-convex shapes in the microstructure. The effective macroscopic response of the samples is computed under the formulation of a set of non-redundant, periodic boundary conditions, which warrants a consistent transition between the microscopic and macroscopic scales. A sample in which austenitic grains are clustered within a ferritic matrix by means of a band-like region is compared to a sample with austenitic grains being randomly dispersed within the ferritic matrix. It is found that the banded microstructure may be detrimental in comparison to the dispersed microstructure, since it allows substantial plastic localization to occur in the ferritic matrix, which in turn diminishes the strengthening effect provided by the austenitic phase.