Influence of the cutting process, heat treatment, and maximum magnetic induction on the magnetic properties of highly oriented electrical steels

In this work, the dynamic losses of modern high-permeability grain-oriented (HGO) electrical steel were investigated as a function of the clearance used during the shear cutting process and the frequency of the applied magnetic field from 3 up to 1000 Hz. The strips were shear cut at clearances of 0.01, 0.04, 0.05, 0.10 and 0.15 mm, and after cutting the samples were heat treated at 850 degrees C for 1 h. The edge regions were analysed using optical microscopy before and after the heat treatment, and a significant mechanical deformation and consequently a deterioration of magnetic properties was observed, which can be restored through stress-relief annealing. Clearances of 0.01, 0.04, 0.05 and 0.10 mm exhibit the same total magnetic loss; however, for the clearance of 0.15 mm, it increases by approximate to 10% due to the crack in the fracture zone and greater rollover region. The heat treatment improves the magnetic performance of the as-cut HGO steel strips by approximate to 8% and approximate to 15% for 1.5 and 1.7 T, respectively, at frequency of 60 Hz. Finally, a detailed study of the dependence of the losses (hysteresis Ph, classical eddy current Pc, and excess Pe) on frequency and maximum induction was performed. Interestingly, it was observed that Ph is much more influenced by clearance than other losses. In addition, the role of the maximum induction Bmax on each loss component was investigated as a function of frequency. Our findings show that below 0.2 T Pc is larger than Pe and Ph, however, above this threshold there is an inversion where Pe is larger than the other two components in the entire frequency range, even with 1.5 T of magnetic induction. This can indicate that different physical mechanisms that constitute the permeability spectrum exhibit different relaxation times, therefore, they are activated at different frequencies and magnetic field intensities.

Automated summary

The study investigated the dynamic losses of modern high-permeability grain-oriented electrical steel, finding that clearance during shear cutting and frequency of the applied magnetic field impact magnetic properties. Heat treatment can restore properties affected by mechanical deformation during cutting. Different clearances result in variations in losses, impacted by frequency and induction intensity.