Magnetic Properties and Microstructure of a FeCo Ferritic Steel after Severe Plastic Deformation

A commercial FeCo ferritic steel with an initial grain size of 10 μm was subjected to Severe Plastic Deformation in a temperature range between 293 K (0.16Tm, Tm: melting temperature in K) and 723 K (0.4Tm) up to strain levels where a saturation of the microstructural refinement is observed. The microstructure of the severely deformed state is analyzed by Back Scattered Electrons micrographs captured in a SEM. The magnetic properties were characterized by means of SQUID-magnetometer providing information about the magnetization behavior of the material in the as processed state. Depending on the deformation temperature mean microstructural sizes in the steady state of 50 nm and 270 nm were observed after SPD at 293 K and 723 K, respectively. These small microstructural sizes influences significantly the magnetic properties of the material: it shifts the behavior from soft-magnetic in the initial coarse grained state towards a hard-magnetic with decreasing size of the crystallites. For sizes of the crystallites smaller than about 100 nm the magnetic properties become again more soft-magnetic.