The mechanical behavior of armco-iron samples under equichannel corner extrusion and torsional deformation and the structure of the deformed samples were studied by the methods of transmission electron microscopy, differential scanning calorimetry, microhardness measurements, and mechanical tests by tension and compression. The ultrafine-grained (UFG) armco iron has good strength (ultimate tensile strength and yield strength are 1400 and 1200 MPa, respectively) and plasticity (30%). The effect of thermal stability of the UFG structure on the Hall-Petch coefficient and the relationship between the microhardness and the yield strength are discussed.