Direct determination of phase stress evolution in duplex steel using synchrotron diffraction

The present work deals with the investigation of the micromechanical behaviour of a duplex steel, which consists of two phases (austenite and ferrite) exhibiting significantly different mechanical properties. The stresses in both phases were experimentally determined in the elastic and plastic ranges of deformation using synchrotron radiation diffraction experiments. The used methodology enabled to determine the values of initial stresses and to study the evolutions of the principal phase stresses and the second order stresses during the elastic, as well as the plastic range of deformation. With the help of a self-consistent model, the critical resolved shear stresses and the work hardening parameters for slip systems, active in each phase, were also estimated. Comparison of the measured phase stresses and lattice strains evolutions with the model results showed a good agreement between prediction and experiment when the initial stress state in the sample and shape of grains approximated by ellipsoidal inclusions were taken into account. The overall outcome of the work is the determination of stress partitioning between the two phases of a polycrystalline material for all deformation stages, determined directly from diffraction experiment. The results enabled analyses of von Mises, hydrostatic stresses as well as second order stresses evolutions in both phases during tensile deformation. Finally, the experimental data were successfully compared with predictions of the self-consistent deformation model.