Degradation of Static and Dynamic Magnetic Properties of Non-Oriented Steel Sheets by Cutting

Abstract

The performances of non-oriented iron-silicon (NO Fe-Si) alloys, which are among the most commonly used materials for soft magnet applications, suffer because of mechanical stresses, whose intensity depends on the cutting technology applied, when these materials are used in the shape of strips in the magnetic core manufacture. This paper presents a detailed analysis of the influence that the stresses, arising from mechanical punching technology, have on the energy losses and normal magnetization curves, measured on NO Fe-Si samples. High-quality Cogent NO20 Hi-Lite and M300-35A samples, having a thickness of 0.2 and 0.35 mm, respectively, with a length of 300 mm, were cut by guillotine shear method to obtain strips with widths varying from 5 to 60 mm. The attained strips having different widths were characterized using a hysteresisgraph-wattmeter to measure ac energy losses and hysteresis cycles in the frequency range from 3 to 1500 Hz for NO20 and up to 400 Hz in the case of M300-35A. The dynamic loss behavior is presented in accordance with the statistical theory of losses, while a low to moderate increase is observed with the sample width decrease. The measured total energy losses were then decomposed into the hysteresis and dynamic components, including the classical and excess energy losses. The energy losses’ behavior as a function of the strip width was, eventually, analyzed and modeled, considering that cutting process induces local hardening on the borders of the samples. The experimental results put also in evidence a hyperbolic variation of the hysteresis losses versus strip width in both cases. As a remarkable result of these considerations, we observe that the evolution of the hysteresis energy losses can be predicted from the very wide, almost undamaged, to narrowest, fully degraded width strips.