Bainitic steels are among the steel grades with the most complex microstructure, which makes the prediction of their mechanical properties challenging. Here we study a bainitic steel that is composed of two phases, granular bainite and polygonal ferrite. To create Representative Volume Elements (RVEs) that incorporate the complexity of the material, we extend an approach originally developed for martensitic microstructures [1] and study the role of different microstructural features on the material performance. The phase fractions were determined based on EBSD scans. The second big challenge, besides the complex microstructure, with respect to crystal plasticity modeling of complex steels is the identification of the material parameters of the different phases. To this end we use a combination of micro pillar compression, nanoindentation, and macroscopic stress-strain tests to determine the parameters for the two phases. Micro-compression tests are carried out to calculate the critical resolved shear stresses for each slip family in both phases. Then in a second step the material parameters of the granular bainite are optimized to match the height profiles of nanoindentation tests on differently oriented grains. Finally RVE simulations are used to determine the parameters of the polygonal ferrite by matching the macroscopic stress-strain curves. The resulting simulation setup is then used to study the difference in performance of two variants of the bainitic steel resulting from different cooling rates [2]. The material with the lower cooling rate has a higher fraction of polygonal ferrite but shows a lower total elongation with a comparable stress-strain behavior. On the basis of the full field simulations, it could be shown that this behavior is probably caused by different damage initiation mechanisms in both materials. REFERENCES [1] Gallardo-Basile F.-J., Naunheim Y., Roters F., Diehl M., Lath Martensite Microstructure Modeling: A High-Resolution Crystal Plasticity Simulation Study. Materials, Special Issue ”Micromechanics: Experiment, Modeling and Theory”, Vol. 14, pp. 692 – 701, 2021. [2] Gallardo-Basile F.-J., Roters F., Jentner R. M., Srivastava K., Scholl S., Diehl M., Modeling Bainite Dual-Phase Steels: A High-Resolution Crystal Plasticity Simulation Study. Crystals, Vol. 13, p. 673, 2023.