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 transforma tion under complex thermomechanical paths, and the development of TRIP plas ticity. The final aim is to provide a criterion, written in terms of temper ature and stresses, to be used for determining both the initiation and the kinetics of martensite transformation and the related TRIP strains. The mod el will be written on a macroscale, so that only one scalar value is introd uced to represent all the martensite variants. The specimens are thin tubes tested on a tension torsion machine, so that multiaxial stress paths can b e applied. The transformation is produced either during cooling tinder cons tant stress or at a given temperature in tensile tests. Both types of tests allow to characterize the onset of the transformation; oil 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 impleme nted into the F.E. code ZeBuLon.