The mechanism of plastic straining and the structure of high-nitrogen austenitic steel 06Kh18AG19M2 (0.81% N) after a hardening treatment involving quenching, aging, and plastic deformation by equichannel angular pressing (ECAP) are studied. Electron microscope investigation is used to determine the mechanism of straining and fragmentation of the structure of the steel under the ECAP, i.e., twinning. The method of x-ray diffraction analysis is used to evaluate the contribution of the parameters of structural flaws into the broadening of austenite lines under the ECAP.