Electrical steel (lamination steel, Non Grain Oriented Silicon Steel, silicon steel, relay steel, transformer steel) is a special steel tailored to produce specific magnetic properties: small hysteresis area causing low power loss per cycle, low core loss, and high permeability.
Electrical steel is generally produced in cold-rolled strips lower 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 could be cut to their finished shape by a punch and die or, in smaller quantities, may be cut with a laser, or by wire EDM.
Electrical steel is definitely an iron alloy which can have from zero to 6.5% silicon (Si:5Fe). Commercial alloys usually have silicon content as much as 3.2% (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum could be added as much as .5%.
Silicon significantly boosts the electrical resistivity of the steel, which decreases the induced eddy currents and narrows the hysteresis loop in the material, thus decreasing 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 has to 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 decreasing magnetic permeability. The presence of carbon features 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 resulting in a rise in power loss as time passes. For these reasons, the carbon level is kept to .005% or lower. The carbon level could be reduced by annealing the steel in a decarburizing atmosphere, such as hydrogen.
Non-oriented Gi Wire (image made out of magneto-optical sensor and polarizer microscope)
Electrical steel made without special processing to manage crystal orientation, non-oriented steel, usually features a silicon amount of 2 to 3.5% and it has similar magnetic properties in every 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 degree of 3% (Si:11Fe). It is processed in such a way that this optimal properties are created in the rolling direction, because of 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% 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 usually abbreviated to CRGO.
CRGO is generally supplied by the producing mills in coil form and has to be cut into “laminations”, which are then used to create a transformer core, which can be an important part of any transformer. Grain-oriented steel can be used in large power and distribution transformers and in certain audio output transformers.
CRNGO is less expensive than CRGO. It is used when expense is more valuable than efficiency and for applications where the direction of magnetic flux will not be constant, like electric motors and generators with moving parts. It can be used if you have insufficient space to orient components to take advantage of the directional properties of Electrogalvanized Steel Coil.