The powders of X20Cr13 steel were subjected to ball milling process in a planetary ball mill. X-ray diffraction and Mossbauer spectroscopy studies revealed the refinement of the structure of this steel down to a nanocrystalline range practically without any phase transformations. Both techniques allowed to detect the alloyed ferrite as well as residual content of iron containing M23C6-type carbide, which was dissolved into the ferrite during milling. Hyperfine magnetic fields in ball milled steel samples did not differ significantly from those for the bulk steel disc.