Modeling bainitic transformations during press hardening - Press Bain
Press hardening is an important processing technology for the production of safety relevant components for automotive applications. The parts are hot formed in the austenitic state in a tool with defined tool temperature below 550 °C and afterwards quenched under load inside this tool. This technology allows forming of complex shaped parts made of ultrahigh strength steels. Depending on quenching conditions martensitic or bainitic microstructures form, with a strong coupling between mechanical load, internal stresses, chemical composition and phase transformation kinetics. To address the effects of external mechanical loads on the transformation-kinetics and plasticity of the bainite transformation, we have performed multiscale and multi-physics modeling as well as experimental research. In particular, a full-field description of the bainitic microstructure by a multi-phase field model is linked to a crystal plasticity model at micrometer scale to simulate the mutual interaction between the phase transformation and plastic accommodation of the lattice distortion for a comparison of crystallographic features, transformation strain and texture of the simulated phase structure to experimental observations.
In particular, we will report on the effect of large deformations and interface relaxation mechanisms on the thermodynamics and kinetics of carbides near austenite-ferrite interfaces on microscopic scales, a mean-field description of bainitic variants (packets) on mesoscopic scales and a full-field description of sheave and packets on macroscopic scales. Furthermore, we will demonstrate the use of machine learning approaches for the prediction of the composition dependent bainite start temperature in the spirit of a “bainite toolbox” development.