Influence of stress on the stray field signals of ferromagnetic materials

To investigate the influence of stress alone on the stray field signals of ferromagnetic materials, the static tensile tests of 0.45%C steel and 45CrNiMoVA steel flat-shaped specimens were performed on an MTS810 hydraulic testing machine. Hp(y) signals, the normal component of spontaneous stray field, were measured during the testing process by an EMS-2003 metal magnetic memory diagnostic apparatus cooperated with a non-magnetic electric control displacement instrument. Fracture and microstructure were observed by a scanning electronic microscope and a transmission electron microscope, respectively. The relationships between axial applied stress or residual stress measured by X-ray diffraction method and Hp(y) were analyzed. The results indicate that some regular pattern of the magnetic curve is displayed only between applied stress and stray field signals. The magnetic ordering process stops due to dislocation pinning magnetic domain structure, and Hp(y) value unvaried nearly with applied load increasing in the plastic deformation stage.