On the effect of material processing: microstructural and magnetic properties of electrical steel sheets

This paper presents both the effect of cutting on the material behavior of a typical used NGO electrical steel grade M230-30A as well as a study of the effect of annealing temperature after cold rolling on microstructure and magnetic properties beginning with an industrial hot rolled 2.4 wt.% Silicon steel of 2.0mm thickness. Modifications in the local mechanical properties due to the cutting process are investigated in detail. A quantitative analysis of the impact of material degradation for non-oriented electrical steels applied in traction drives is presented. In order to consider the large speed range of drives in automotive applications and the presence of higher harmonics, this analysis is conducted for a wide range of frequencies and magnetic polarizations. Nanoindentation is used to analyze the effect of strain from cutting on the hardness near the surface. A major conclusion is that it is indispensable to take into account influences due to material processing on magnetic materials properties during the design process of electrical machines.