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.