Effect of tensile plastic deformations on the residual magnetization and initial permeability of low-carbon steels

The behavior of residual magnetization Mr, initial magnetic permeability μ, and coercive force Hc of steels subjected to plastic extension both in the loaded state and in the unloaded state during “slow” and “fast” loading is explained from a unified point of view. It is shown that, upon unloading, the appearance of residual compressive stresses along the direction of the applied force in a considerable portion of grains leads to an abrupt decrease in Mr and μ and to an equally sharp increase in Hc. A slow decrease in Mr and μ and an equally slow increase in Hc are observed in the loaded state with an increase in ε; this effect is caused by an increase in the dislocation density. The values of Mr, μ, and Hc in the transition region of ε ≤ εcr obtained under slow loading differ considerably from those obtained under fast loading. In loaded and unloaded states, the dependences of Mr, μ, and Hc on ε are identical at ε ≥ εcr. The results obtained will be important when the magnetic parameters analyzed in this study are used for nondestructive testing of steel structures that have plastic deformations.