Electrical steel (lamination steel, Crngo, silicon steel, relay steel, transformer steel) is a special steel tailored to produce specific magnetic properties: small hysteresis area leading to 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 that are stacked together to create the laminated cores of transformers, and the stator and rotor of electric motors. Laminations might be cut to their finished shape by a punch and die or, in smaller quantities, could be cut by way of 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 could be added up to .5%.
Silicon significantly increases the electrical resistivity from the steel, which decreases the induced eddy currents and narrows the hysteresis loop from the material, thus lowering the core loss. However, the grain structure hardens and embrittles the metal, which adversely affects the workability from 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 existence of carbides, sulfides, oxides and nitrides. These compounds, even just in particles no more than one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The presence of carbon has a more detrimental effect than sulfur or oxygen. Carbon also causes magnetic aging when it slowly leaves the solid solution and precipitates as carbides, thus causing a rise in power loss with time. For these reasons, 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 Gi Wire (image made with magneto-optical sensor and polarizer microscope)
Electrical steel made without special processing to regulate crystal orientation, non-oriented steel, usually features a silicon degree of 2 to 3.5% and contains similar magnetic properties in all directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is usually abbreviated to CRNGO.
Grain-oriented electrical steel usually has a silicon level of 3% (Si:11Fe). It is actually processed in a way that the optimal properties are developed 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 actually used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is usually abbreviated to CRGO.
CRGO is normally supplied by the producing mills in coil form and must 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 as well as in certain audio output transformers.
CRNGO is less expensive than CRGO. It really is used when cost is more valuable than efficiency and then for applications where the direction of magnetic flux is not really constant, like electric motors and generators with moving parts. It can be used when there is insufficient space to orient components to benefit from the directional properties of Electrogalvanized Steel Sheet.