Influence of applied tensile stress on the hysteresis curve and magnetic domain structure of grain-oriented Fe–3%Si steel

Abstract

The influence of applied tensile stress on the hysteresis curve and domain structure in conventional (1 1 0)[0 0 1] Fe–3%Si steel, cut parallel to the rolling direction, is studied on samples with different grain sizes. Quasistatic hysteresis loops under tensile stresses up to 70 MPa were measured. The magnetic domains and magnetization processes were observed by longitudinal Kerr microscopy at different levels of stress. It is shown that for stresses exceeding 5–10 MPa the bulk hysteresis loop can be described with good accuracy by the action of an effective field, which is the product of a function of stress and a function of magnetization. The function of stress is approximately linear with a slope of one. Except for the sample with the smallest grains, the function of magnetization is linear in the magnetization range ±1.2–1.5 T, i.e. it has a typical demagnetizing field shape. Domain observation reveals that the effective field is caused by the demagnetizing fields occurring at grain boundaries and at the sheet surface due to the removal of closure domains transverse to the rolling direction by the tensile stress. The closure structure reappears at higher fields. Another indirect indication of demagnetizing fields is the fact that the hysteresis losses drop continuously with stress and changes in the coercive force are small. The effective field of the sample with the smallest grains increases most nonlinearly with stress similar to the behaviour obtained for non-oriented material.