Magnetic Ageing of Electrical Steel: Precipitates Impact on Magnetic Losses

In this work, a high permeability grain-oriented electrical steel (HGO) was subjected to heat treatment to promote the magnetic ageing of the material. The magnetic properties, microstructure and precipitate formation of two samples, one with 38 ppm of C (sample 622A) and another with 18 ppm of C (256B), were investigate before and after of the heat treatment (ageing) at the temperature of
$\mathbf{229}\pm \mathbf{3}\ {{}^{\circ}\mathbf{C}}$
, which is approximately to that of power transformer operation. The magnetic loss of all samples in the frequency range from 10 to 60 Hz at 1.5 T was analyzed before and after annealing. It was found that there is an increase in magnetic loss in the heat treated samples, indicating the impactcof possible precipitates on the magnetization dynamics. Furthermore, the loss components (hysteresis, classical and excess) were determined as a function of frequency, and we observed that the hysteresis loss dominates at low frequencies (<50 Hz) and above this the excess loss becomes dominant, and this threshold is different for the two samples studied. This indicates that precipitates play a fundamental role in the movement of the material's domain walls, since excess loss is known to be associated with microcurrents induced by this physical mechanism.