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.