The consequences of cold deformation phase transformation in chromium–nickel steel 12Kh18N10T have been studied. A metallographic study of samples has been performed with an increase of up to ×10 000 and an increase in the proportion of martensite in austenitic steel as a result of cold plastic deformation has been shown. A durometric study has been carried out, and the character of metal hardening with increasing degree of deformation has been confirmed, which shows the presence of at least two hardening mechanisms: deformation and phase. A magnetic study has been carried out, and the intensity of the growth of the magnetic phase with increasing deformation has been revealed. A comparison is made with the known data on the intensity of the martensitic transition for the same grade of chromium–nickel steel under cold deformation conditions.