The macro- and micromechanics of TRIP-assisted multiphase steels, experiments and modeling

TRIP-assisted multiphase steels exhibit enhanced strength and ductility properties. These properties result from the unique combination of various work-hardening and damage mechanisms taking place in a multiphase microstructure consisting of an intercritical ferrite matrix with a dispersion of bainite + martensite + metastable retained austenite grains. Martensite plays a crucial role in these mechanisms for the improvement of plastic properties (through the TRIP effect, i.e. the mechanically-induced martensitic transformation), and also, in the damaging process. This study aims at establishing how martensitic transformation influences the mechanical properties (plasticity and fracture) when occurring in a multiphase microstructure. On the one side, macro- and micromechanical tests, SEM and TFM, Mossbauer spectroscopy and x-ray diffraction are used to characterise the mechanisms of deformation, transformation, and fracture at the various relevant scales. On the other side, computational unit cell models are employed for assisting (i) the development of micromechanically-based constitutive models, (ii) the interpretation of experimental results.