Commonly used transformer cores are generally made of silicon steel sheets. Silicon steel is a kind of steel containing silicon (silicon is also called silicon), and its silicon content is 0.8~4.8%. The iron core of the transformer is made of silicon steel because silicon steel itself is a magnetic substance with strong magnetic permeability, and it can generate a large magnetic induction intensity in the electrified coil. Therefore, the size of the transformer can be reduced.

Silicon is a good deoxidizer for steel. It combines with oxygen to convert oxygen into stable SiO2 that is not reduced by carbon, avoiding the lattice distortion of iron due to oxygen atom doping. After silicon becomes a solid solution in α-iron, the resistivity increases, and at the same time, it helps to separate the harmful impurity carbon. Therefore, adding silicon to iron containing impurities can increase the magnetic permeability, reduce the coercive force and iron loss. However, the increase in silicon content will make the material hard and brittle, and the thermal conductivity and toughness will decrease, which is not good for heat dissipation and machining. Therefore, the silicon content of silicon steel sheets generally does not exceed 4.5%.

There are two types of silicon steel sheets, cold-rolled and hot-rolled, and cold-rolled silicon steel sheets are used more. Cold-rolled silicon steel sheet has excellent magnetic properties along the rolling direction, not only has high saturation magnetic flux density and low iron loss in strong magnetic field, but also has good magnetic properties (large initial magnetic permeability) in weak magnetic field. This is because the cold rolling process reduces the impurity content in the steel sheet and causes coarse grains in the steel sheet, resulting in an increase in magnetic permeability and a decrease in hysteresis loss.

In order to increase the magnetic induction intensity, an iron core is used in the transformer. When the alternating current passes through the coil of the transformer, a large eddy current will be generated in the iron core, which not only saves a lot of energy, but may even burn these devices. In order to reduce the eddy current and its loss, the stacked silicon steel sheet is usually used to replace the whole iron core and the plane of the silicon steel sheet is parallel to the magnetic induction line. On the one hand, due to the high resistivity of the silicon steel sheet itself, on the other hand, the insulating varnish or natural insulating oxide layer is applied between the sheets, so that the eddy current is limited in each sheet, so that the eddy current is greatly reduced, thereby reducing power loss.

As the iron core of the transformer, cold-rolled silicon steel sheets with a thickness of 0.35mm are generally used. According to the size of the required iron core, it is cut into long pieces, and then overlapped into a "day" or "mouth" shape. Theoretically speaking, in order to reduce eddy current, the thinner the thickness of the silicon steel sheet and the narrower the spliced strips, the better the effect. This not only reduces the eddy current loss and temperature rise, but also saves the material used for silicon steel sheets. But in fact when making silicon steel sheet core. Not only starting from the above-mentioned favorable factors, because making the iron core in that way will greatly increase the man-hours and also reduce the effective cross-section of the iron core. Therefore, when using silicon steel sheets to make transformer cores, it is necessary to proceed from the specific situation, weigh the pros and cons, and choose the best size.