This work is based on the use of electron backscatter diffraction (EBSD) methods to investigate the microstructure of metastable austeniticsteel 12X18Н10T (321) after cryogenic rolling. Cryogenic deformation was accompanied by martensitic transformations, and the martensitic phase nucleation mainly in deformation bands. It is assumed that the proceeding of the martensitic transformation in the most deformed parts of the microstructure should prevent the evolution of deformation-induced boundaries in the austenite and, thus, inhibit the process of fragmentation of this phase. Mechanical twinning was the primary (or even sole) mechanism providing HAB formation in the austenite.