Methods of magnetic powder patterns (Bitter technique), optical microscopy, and transmission electron microscopy have been used to study the formation of martensite in a spherical sample of 12Kh18N10T steel upon loading by quasi-spherical converging shock waves. Prior to loading, the steel exhibited carbide banding (TiC and Cr 23 C 6 carbides were located in bands along the axis of the initial sample). It has been shown that, upon loading, disperse crystals of martensite are formed in these carbide-containing bands. No martensite was formed in the central part of the solid sphere, in the surface layers, and in the Altshuler-pattern rays. It has been concluded that, in these regions, the temperature exceeded the M d temperature, above which the deformation does not cause a martensitic transformation.