Characterisation of microstructure and modelling of flow behaviour of bainite-aided dual-phase steel

• Combined EBSD and EPMA were applied to quantify bainite in commercial DP steel.
• 2D RVEs were created based on KAM and EPMA carbon distribution map.
• Flow curve of bainite was modelled using dislocation density based approach.
• Influence of small bainite fraction on macroscopic behaviour was quantified.
• Taking into account bainite in RVE approach yields improved flow curve prediction.

This study aims to characterise the microstructure and model the flow curve behaviour of bainite-aided DP steel. First, combined electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) measurements were applied to quantify the constituents (ferrite, martensite, and bainite) in the microstructure. Then, the flow behaviour of the material was modelled using the microscale finite element method by considering the effect of the microstructures using the representative volume element (RVE) approach based on real microstructure. The flow behaviour of single phases (ferrite, martensite, and bainite) was modelled using the dislocation-density-based work-hardening approach, whereas the model parameters were identified using microstructural features. The flow curves predicted from the 2D RVE calculations were correlated to 3D using a correlation factor. Good agreement between the 3D correlated and experimental flow curves was only achieved when bainite was considered in the RVE modelling. The presence of bainite reduces the internal stress gradients while increasing the overall strength of the material.