The structure and the behavior of ferrite-carbide mixtures in steels upon plastic deformation have long been studied in much detail, but the mechanism of loss of plasticity and of changes in these steels in the range of large plastic deformations are unclear up to date. The problem of the effect of large plastic deformations on the magnetic properties of steels also remains insufficiently studied. Therefore, we have studied mechanical and magnetic properties and mechanisms of damage in the range of large plastic deformations with the aim to clarify factors responsible for the sharp drop of plasticity in cold-worked wire.