Magnetic Behavior of NO Fe-Si Sheets under Tensile and Compressive Stress

The stress dependence of the magnetic properties of non-oriented Fe-Si steel sheets has been investigated by measurement and analysis of hysteresis loop, magnetization curve, and energy losses taken at different peak polarization values J (0.5 T – 1.5 T) between DC and f = 400 Hz. The salient feature of the material response to the stress lies in the monotonic deterioration of the soft magnetic properties, across the whole (J - f) domain, on passing from the maximum tensile stress (σ = +30 MPa) to the maximum compression (σ = -30 MPa). This is understood in terms of stress-induced redistribution of the domains between easy axes, making magnetic hardening by compression directly related to unfavorably directed domains and 90° domain-wallmediated magnetization transitions. The loss decomposition is carried out across the whole investigated frequency range, taking into account the skin effect at the highest frequencies. Quasi-static and dynamic losses follow a same trend with σ, both monotonically increasing on passing from the tensile to the compressive stress limits, according to the theoretically expected relationship existing between the hysteresis and the excess loss components. The latter is shown to identify the correlation regions where the magnetization is reversed of size comparable with the average grain size and loosely following the dependence of the loss figure on the applied stress.