Study of the martensitic transformation on a Cr-Ni-Mo-Al-Ti steel for different thermomechanical paths

The purpose of this paper is a study of the onset of martensitic transformation under complex thermomechanical paths, and the development of TRIP plasticity. The final aim is to provide a criterion, written in terms of temperature and stresses, to be used for determining both the initiation and the kinetics of martensite transformation and the related TRIP strains. The model will be written on a macroscale, so that only one scalar value is introduced to represent all the martensite variants. The specimens are thin tubes tested on a tension torsion machine, so that multiaxial stress paths can be applied. The transformation is produced either during cooling under constant stress or at a given temperature in tensile tests. Both types of tests allow to characterize the onset of the transformation; on the other hand, a full modeling of the test under constant load is proposed, and compared with a classical approach. The new constitutive equations have been implemented into the F.E. code ZeBuLon.