Impact of grain size distribution on the magnetic deterioration due to cutting of electrical steel sheets

Efforts to increase the power density and continuous power of electric machines have intensified the request for tailored non-grain oriented electrical steel grades. Possible measures to optimize electrical steel grades are the use of thinner gauges as well as grades with tailor-made microstructural properties. However, these grades are developed mainly focusing on the magnetic and mechanical properties, neglecting the detrimental and strongly material-dependent processing effect on the magnetic properties of electrical steel, especially the cutting influence. In this paper, the microstructure-dependence of the magnetic material deterioration due to guillotine cutting is studied on ten industrial non-grain oriented electrical steels with thicknesses between 0.1mm and 0.35mm, all of which the chemical composition, grain structure and texture is known. This allows a consideration of the interdependence of material thickness, microstructure, alloy content with the cutting effect. The magnetic deterioration is characterized on a single-sheet-tester with samples in rolling as well as transverse direction. The grain size distribution and homogeneity is evaluated and linked to magnetic-loss and magnetization-curve deterioration by means of statistical methods. As a result sheet-thickness-dependent microstructures are evaluated with respect to their cutting influence.