Electrical steel (lamination steel, Crngo, 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 shape to make laminations which can be stacked together to create the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut to their finished shape by way of a punch and die or, in smaller quantities, may be cut by a laser, or by wire EDM.
Electrical steel is 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 can be added up to .5%.
Silicon significantly increases the electrical resistivity in the steel, which decreases the induced eddy currents and narrows the hysteresis loop in the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from the material, especially when rolling it. When alloying, the concentration degrees of carbon, sulfur, oxygen and nitrogen should be kept low, because these elements indicate the existence of carbides, sulfides, oxides and nitrides. These compounds, even during particles as small as one micrometer in diameter, increase hysteresis losses while decreasing magnetic permeability. The presence of carbon includes a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging if it slowly leaves the solid solution and precipitates as carbides, thus leading to a rise in power loss with time. Because of this, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in a decarburizing atmosphere, like hydrogen.
Non-oriented Gi Wire (image created using magneto-optical sensor and polarizer microscope)
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually features a silicon amount of 2 to 3.5% and has similar magnetic properties in every directions, i.e., it really is isotropic. Cold-rolled non-grain-oriented steel is often abbreviated to CRNGO.
Grain-oriented electrical steel usually features a silicon amount of 3% (Si:11Fe). It is actually processed in such a way that this optimal properties are developed in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation in accordance with the sheet. The magnetic flux density is increased by 30% inside the coil wnhsva direction, although its magnetic saturation is decreased by 5%. It is actually utilized for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is usually provided by the producing mills in coil form and has to be cut into “laminations”, which are then used to form a transformer core, that is a fundamental element of any transformer. Grain-oriented steel is used in large power and distribution transformers and in certain audio output transformers.
CRNGO is less expensive than CRGO. It is actually used when expense is more valuable than efficiency as well as for applications where direction of magnetic flux is not constant, as in electric motors and generators with moving parts. You can use it should there be insufficient space to orient components to benefit from the directional properties of Electrogalvanized Steel Coil.