At low strains (e < 0.25), the precipitation of Ti, Nb, V carbides in austenitic Fe -Mn -C steels which exhibit twinning induced plasticity has no significant effect on work hardening. Strengthening follows the Orowan mechanism and can be described by a simple yield stress offset. However, at higher strains (e > 0.3) the work hardening rate decreased slightly. Synchrotron X-ray diffraction analysis suggested that this was due to a reduction in the kinetics of twin formation. The highest strengthening coefficient in cold strips was obtained with Ti additions £ 0.1 wt.% (+1 380 MPa/ wt.% Ti) but the effect quickly saturated after an increase of *+150 MPa. With Nb additions only modest hardening (+187 MPa/wt.%) could be achieved. The strengthening due to V was > 530 MPa/wt.% for V additions £ 0.4 wt.% Saturation effects are less critical with V additions and yield stress increases of +375 MPa were demonstrated.

The deformation mechanisms of an Fe-Mn-C TWIP steel have been investigated as a function of deformation and deformation temperature, using synchrotron X-ray diffraction at the European synchrotron radiation facility. Using the Warren theory, it is possible to reach a good qualitative understanding of the deformation mechanisms. We have confirmed that the deformation mechanisms shifted from the formation of martensite at very low temperature, to twinning around room temperature and dislocations at higher temperatures. Although some quantification of the density of crystalline defects can be reached using simple parameters such as peak shift and broadening, the complexity of defects present in this material require the development of more advanced data interpretation models. First results are shown, using shift and broadening of the peak and fit of intensity by a pseudo-voigt function, as well as the study of the asymptotic behavior of the intensity.

Fully austenitic steels of the Fe-Mn-C system can show extensive deformation twinning (TWIP effect). The deformed microstructure of such steels has been analysed using X-ray diffraction at the European Synchrotron Radiation Facility (ESRF). The experimental diffractograms, recorded using a 2D CCD camera, are analysed in terms of Bragg peak profiles (broadening and asymmetry) and position (shift from the reference [undeformed state] position) leading to an estimation of dislocation and stacking faults densities.