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 manufactured in cold-rolled strips lower than 2 mm thick. These strips are cut to shape to make laminations that are stacked together to create the laminated cores of transformers, as well as the stator and rotor of electric motors. Laminations may be cut to their finished shape with a punch and die or, in smaller quantities, could be cut by 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 usually have silicon content as much as 3.2% (higher concentrations usually provoke brittleness during cold rolling). Manganese and aluminum may be added approximately .5%.
Silicon significantly boosts the electrical resistivity in 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 amounts 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 just in particles as small as one micrometer in diameter, increase hysteresis losses while also decreasing magnetic permeability. The existence of carbon features 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 an increase in power loss with time. 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, like 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 includes a silicon amount of 2 to 3.5% and has similar magnetic properties in most 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 degree of 3% (Si:11Fe). It is actually processed in a way that this optimal properties are developed in the rolling direction, because of a tight control (proposed by Norman P. Goss) in the crystal orientation relative to 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 used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.
CRGO is generally provided by the producing mills in coil form and needs to be cut into “laminations”, that are then used to create a transformer core, which can be an important part of any transformer. Grain-oriented steel is utilized in large power and distribution transformers and in certain audio output transformers.
CRNGO is less expensive than CRGO. It is actually used when price is more valuable than efficiency and then for applications in which the direction of magnetic flux is not really 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 Electro Galvanized Steel.