The transformation between the face centered cubic austenitic and hexagonal close-packed martensitic phases during high-pressure torsion processing was observed in a Fe-Mn-C-Al twinning-induced plasticity steel. This phase transformation was not found in the same material processed by unidirectional compressive and tensile deformation. Initiated by the high-pressure loading, the martensite phase initially increased with torsional strain but diminished subsequently. Texture evolution of the austenitic phase was compared with the ideal texture distribution of face-centered cubic materials after shear deformation. High pressure torsion of TWIP steel shows the formation of an HCP Martensite phase, whose volume fraction first increases, then decreases with increasing strain, as shown by local synchrotron diffraction at various points along the radius of the sample, and neutron diffraction on samples with increasing number of turns. Local texture analysis shows the correlation between position and predominant deformation mechanism.