Magnetic Properties of Electrical Steel Sheets in Respect of Cutting: Micromagnetic Analysis and Macromagnetic Modeling

This paper provides a quantitative analysis of the degradation of the magnetic properties of nonoriented electrical steel sheets caused by laser, guillotine, and spark erosion cutting as well as the healing effect of stress relief annealing. For this purpose, the macroscopic material characteristics, such as commutation curves, dynamic hysteresis loops, and magnetic power losses, are gained by single-sheet tester measurements. The experiments are conducted on specimens composed of strips of variable width to adjust different degrees of total degradation. The origin of the observed changes of the material is elucidated by micromagnetic measurements based on the magneto-optical Kerr effect that visualizes the domain patterns and wall movements near the cutting edges. A local magnetic contrast is defined, which serves as a quantitative measure for the local degree of deterioration. The use of homogenous parameters within a numerical loss model based on the principle of loss separation is theoretically justified and experimentally proved to provide correct values of the total magnetic power loss for arbitrary magnetizations in degraded steel sheets.