Magnetic Barkhausen Noise Analysis of Non-oriented Electrical Steels

Monitoring the magnetic quality of non-oriented electrical steel (NOES) laminations during soft magnetic core manufacturing processes is an essential procedure to ensure the energy efficiency of electric motors, since the core loss, which is closely related to the magnetic properties of the laminations, is a major part of the energy loss in electric motors. The cutting of electrical steel sheets into laminates and the assembling of laminates into the final motor core may all induce stresses in the steel, and hence deteriorate the core’s magnetic performance. The present work characterizes four NOES samples with different percentages of silicon (0.88, 1.8, 2.8, and 3.2 wt. %) through magnetic Barkhausen noise (MBN) analysis and investigates the effect of stress on the MBN response. While the MBN energy increases in the direction of applied stress in all samples, the rate of increase is different among different samples. The differences are attributed to the combined effect of stress and domain wall (DW) pinning density. The pinning density is associated with silicon content, i.e., the higher the % Si, the higher the pinning density. Under applied stress, the MBN increases, which is associated with an increase in the number of 180˚ DWs. However, when the interval of the DW spacing becomes less than the jump distance between pinning sites, no further increase of the MBN with stress is observed. Indeed, samples with the lowest % Si exhibit the least stress dependence and saturate first when the MBN is normalized by the zero-stress value. NOES samples are characterized by electron backscatter diffraction (EBSD) to reveal the microstructure and crystallographic texture, which also affect the MBN response.