Loss decomposition in plastically deformed and partially annealed steel sheets

There is increasing interest in the optimization of non-oriented electrical steels for applications under excitation frequencies above 400 Hz. We discuss in this paper the possibility of a new manufacturing procedure, where skin-pass and subsequent heat treatment for recovery are applied as the two last stages of sheet processing. Samples from a commercial non-oriented 3 wt% silicon steel were submitted to 2.5% thickness reduction and were heat treated at temperatures ranging between 600 and 850 degrees C for 2 h. It is shown that, although the hysteresis loss increases with plastic deformation, the excess loss decreases in such a way that under increasing magnetizing frequencies the total energy loss of the deformed and recovered sample becomes lower than in the starting material. The higher the annealing temperature the lower the frequency at which crossover of the loss curves is observed, as long as full recrystallization does not occur. It is assumed that with the dislocation structures left in the deformed and partially recovered samples one achieves a condition of increased fragmentation of the magnetization process, that is, of increased number of concurring correlation regions (Magnetic Objects). The corresponding decrease of the excess loss component can eventually overcompensate the deterioration of the quasi-static magnetic properties, leading to lower total losses.