Electrical steel (lamination steel, Non Grain Oriented Steel, silicon steel, relay steel, transformer steel) is a special steel tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally produced in cold-rolled strips less than 2 mm thick. These strips are cut to contour around make laminations which can be stacked together to form the laminated cores of transformers, and also the stator and rotor of electric motors. Laminations might be cut with their finished shape by a punch and die or, in smaller quantities, might be cut with a laser, or by wire EDM.
Electrical steel is definitely an iron alloy which may have from zero to 6.5% silicon (Si:5Fe). Commercial alloys will often have silicon content as much as 3.2% (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum may be added as much as .5%.
Silicon significantly increases the electrical resistivity in the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus decreasing the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability of the material, particularly when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen must be kept low, as these elements indicate the actual existence of carbides, sulfides, oxides and nitrides. These compounds, even during particles no more than one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The actual existence of carbon includes a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging in the event it slowly leaves the solid solution and precipitates as carbides, thus causing a rise in power loss with time. Because of this, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, like hydrogen.
Non-oriented Galvanized Iron Wire (image created using magneto-optical sensor and polarizer microscope)
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually has a silicon level of 2 to 3.5% and contains similar magnetic properties in most directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon amount of 3% (Si:11Fe). It is actually processed in a way the optimal properties are created in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% within the coil wnhsva direction, although its magnetic saturation is decreased by 5%. It is utilized for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is generally supplied by the producing mills in coil form and has to be cut into “laminations”, which can be then used to make a transformer core, which can be a fundamental element of any transformer. Grain-oriented steel can be used in large power and distribution transformers and then in certain audio output transformers.
CRNGO is cheaper than CRGO. It really is used when expense is more important than efficiency and then for applications where direction of magnetic flux is not constant, as with electric motors and generators with moving parts. You can use it when there is insufficient space to orient components to take advantage of the directional properties of Electrogalvanized Steel Coil.