Electrical steels

Electrical steels Electrical steel is kind of special steel which is tailored to exhibit certain specific magnetic properties such as small hysteresis area (small energy dissipation per cycle or low core loss) and high permeability. It is also called lamination steel, silicon (Si) steel, silicon electrical steel or transformer steel. The steel contains specific percentage of silicon in it which is responsible for its unique property.  In mild steel there is much loss in electrical energy due to hysteresis and eddy current and hence use of mild steel is uneconomical when it is used in the electrical devices. The hysteresis loss is shown in Fig.1.  The hysteresis loss is proportional to the area of the respective loops shown in the figure.                             Fig 1 Comparison of hysteresis loss in electrical steel (left) and mild steel (right) Electrical steel is an iron alloy of iron which may have from zero to 6.5 % silicon but usually has silicon content up to 3.2 % (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum can be added up to 0.5 %. Silicon significantly increases the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop of the material, thus lowering the core loss. However due to the silicon the grain structure hardens and embrittles the steel, which adversely affects the workability of the steel, especially during rolling. When alloying, the concentration levels of carbon, sulphur, oxygen and nitrogen should be kept low since these elements indicate the presence of carbides, sulphides, oxides and nitrides in the steel. These compounds, even in particles sizes as small as one micrometer in diameter, increase hysteresis losses and decrease magnetic permeability. The...