Critical assessment of the micromechanical behaviour of dual phase and trip-assisted multiphase steels

The strength and formability properties of high performance steels have been recently improved thanks to the combination of several strengthening mechanisms such as dislocation strengthening and mechanically-induced martensitic transformation within complex microstructures. These finely grained metastable microstructures are generated during controlled multistage thermomechanical treatments involving several phase transformations. However, the way the different active mechanisms combine in order to improve the properties of these steels is not yet clearly established. The present study proposes an overview of an experimental program devoted to the micromechanical characterisation of Dual Phase and TRIP-assisted multiphase steels. Thanks to different techniques such as X-Ray and neutron diffraction, strain mapping and transmission electron microscopy (TEM), it was possible to characterize the flow behaviour of the different constitutive phases and to measure the critical parameters of the microstructures responsible for the work hardening capabilities of the TRIP-assisted multiphase steels. Comparison of the experimental stress and strain partitioning within the heterogeneous microstructures with the predictions of different modelling assumptions was also carried out.