Evolution of the Piezomagnetic Field of Ferromagnetic Steels Subjected to Cyclic Tensile Stress with Variable Amplitudes

In this research, the evolutions of the piezomagnetic fields of ferromagnetic steels under cyclic tensile stress with variable amplitudes were investigated. The piezomagnetic signals of initially undemagnetized Q345 and U75V steel samples were measured by an APS 428D fluxgate magnetometer. It was found that the magnetic field reversal points vary perceptibly in the initial cycles, and then relax to a more gradual rate of change. The drastic variations of the magnetic field reversals may be utilized to characterize the early stages of plastic deformation. The discontinuous piezomagnetic behaviors occurred during the loading process reveal that the piezomagnetic field is highly sensitive to stress and microstructural changes. The total magnetic fields and the irreversible magnetic fields show apparently different variation characteristics in the elastic and plastic stages. Based on the theory of the interaction between dislocation and domain wall, as well as the related models of the magneto-mechanical effect, the experimental results are discussed.