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 usually manufactured in cold-rolled strips under 2 mm thick. These strips are cut to contour around make laminations that are stacked together to make the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations might be cut for 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 an iron alloy which may have from zero to 6.5% silicon (Si:5Fe). Commercial alloys normally have silicon content approximately 3.2% (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum could be added approximately .5%.
Silicon significantly raises 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 of the material, especially when rolling it. When alloying, the concentration amounts of carbon, sulfur, oxygen and nitrogen has to be kept low, because 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 if it slowly leaves the solid solution and precipitates as carbides, thus resulting in a rise in power loss with time. Therefore, the carbon level is kept to .005% or lower. The carbon level can be reduced by annealing the steel in a decarburizing atmosphere, such as hydrogen.
Non-oriented Hot Dip Galvanized Steel Wire (image made out of magneto-optical sensor and polarizer microscope)
Electrical steel made without special processing to control crystal orientation, non-oriented steel, usually features a silicon amount of 2 to 3.5% and has similar magnetic properties in all directions, i.e., it is actually isotropic. Cold-rolled non-grain-oriented steel is frequently abbreviated to CRNGO.
Grain-oriented electrical steel usually includes a silicon degree of 3% (Si:11Fe). It is actually processed in a manner the optimal properties are created in the rolling direction, as a result of 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 really is employed for the cores of power and distribution transformers, cold-rolled grain-oriented steel is frequently abbreviated to CRGO.
CRGO is normally provided by the producing mills in coil form and must be cut into “laminations”, that are then used to form a transformer core, that is an integral part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers as well as in certain audio output transformers.
CRNGO is less expensive than CRGO. It is used when price is more valuable than efficiency and for applications where direction of magnetic flux is not really constant, like electric motors and generators with moving parts. You can use it if you have insufficient space to orient components to take advantage of the directional properties of Electrogalvanized Steel Coil.