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

TRIP-assisted multiphase steels exhibit enhanced strength and ductility pro perties. These properties result from the unique combination of various wor k-hardening and damage mechanisms taking place in a multiphase microstructu re consisting of an intercritical ferrite matrix with a dispersion of baini te + 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 transfo rmation), and also, in the damaging process. This study aims at establishin g how martensitic transformation influences the mechanical properties (plas ticity and fracture) when occurring in a multiphase microstructure. On the one side, macro- and micromechanical tests, SEM and TFM, Mossbauer spectros copy and x-ray diffraction are used to characterise the mechanisms of defor mation, 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 in terpretation of experimental results.