Yield point phenomenon in low-alloyed TRIP-aided steel: role of retained austenite

Multiphase TRIP-aided steels are generally characterised by a continuous yielding behaviour. The processing route involving a deformation step in the intercritical (ferrite + austenite) region showed an undesirable discontinuous yielding. This is attributed to the formation of fresh dislocations in the soft ferrite matrix that trap the diffusing carbon and form Cottrell atmospheres. The discontinuous yielding disappears when fresh mobile dislocations are introduced through transformation of the retained austenite to martensite.