Silicon steel sheets are a type of soft magnetic material widely used in the electrical engineering field. They are usually rolled into large standard-sized sheets or strips, commonly known as electrical steel sheets abroad, and are extensively used in motors, generators, transformers, electromagnetic mechanisms, relays, electronic devices, and measuring instruments.
Silicon steel sheets are divided into cold-rolled and hot-rolled types, with cold-rolled silicon steel sheets being the most widely used. Cold-rolled silicon steel sheets exhibit excellent magnetic properties along the rolling direction; not only do they possess high saturation magnetic induction and low core loss in strong magnetic fields, but they also demonstrate good magnetic properties (high initial permeability) in weak magnetic fields.
Cold-rolled silicon steel is further categorized into cold-rolled non-oriented silicon steel and cold-rolled grain-oriented silicon steel strips.
Magnesium oxide is generally applied in the coatings of grain-oriented silicon steel, which is used in motor and transformer cores. To meet the electro-physical requirements of the core, the production process of grain-oriented silicon steel sheets involves a high-temperature annealing process at 1200–1250°C. In order to allow the iron metal atoms to achieve an orderly oriented arrangement during annealing and simultaneously form an excellent insulating film on the surface of the silicon steel sheets, this process takes 7 days to complete. Under such high temperatures for a prolonged period, to prevent the silicon steel sheets from fusing into a solid lump of iron, a high-temperature annealing separator is usually coated between the silicon steel sheets to prevent sintering. Magnesium oxide is typically added to this coating.
Silicon steel coatings utilize light-burned 98 or heavy-burned 98 magnesium oxide, or analytical-grade light magnesium oxide as an additive. The addition proportion of magnesium oxide in the coating is about 25%. The primary requirements for magnesium oxide indicators are low levels of SO4, Cl, and Fe, which should be controlled at around 0.01%. It is mainly used as a high-temperature annealing separator and insulating coating formation agent during the manufacturing process of silicon steel, as well as a dephosphorization and desulfurization agent in steelmaking.
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