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2023-10-27
As one of the most important soft magnetic materials today, silicon steel is extensively used in a variety of electronics, power, and military industries. It ranges from a few ounces for small relays or pulse transformers to several tons for generators, motors, and transformers. Therefore, silicon steel has become an indispensable alloy material in our daily lives. But what exactly is silicon steel? Follow us now. We’re going to explore what it is, how it’s made, why we use it, and where we use it!
Silicon steel, also known as electrical steel or silicon electrical steel, is a ferrosilicon(Si-Fe) soft magnetic alloy with extremely low carbon content (＜0.8%) and high silicon content (0.4%-4.5%) in weight. It is mainly used to produce certain magnetic cores, such as stators and rotors in transformers and motors.
Silicon is a good deoxidizer for steel. It can combine 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. Besides, silicon can become a solid solution in α-iron, which increases the resistivity and helps separate harmful impurities carbon. Therefore, iron containing impurities can add silicon elements to increase the magnetic permeability and reduce coercive force and iron loss, thus forming silicon steel. However, increasing the silicon content will make the material hard and brittle, and the thermal conductivity and toughness will decrease, which is detrimental to heat dissipation and mechanical processing. Therefore, the silicon content of silicon steel generally does not exceed 4.5%.
Silicon steel can be classified into different categories according to different partition criteria like silicon content, making method, usage, and shape. Let’s see them one by one.
| Name | Silicon Content | Thickness | Function |
| Low Silicon Steel | ＜2.8％ | 0.5mm | has some certain mechanical strength |
| High Silicon Steel | 2.8％-4.8％ | 0.35mm | magnetic but brittle |
Silicon steel is often manufactured by rolling processes, including hot rolling and cold rolling.
Hot Rolled Silicon Steel
Hot-rolled silicon steel is made by melting Fe-Si alloy in an open furnace or electric furnace, repeatedly hot-rolling it into a thin plate, and finally annealing it at 800-850°C. This type has low availability and high energy loss, which has been gradually phased out.
Cold Rolled Silicon Steel
Silicon steel is produced through a process called cold rolling, where the alloy is rolled into thin sheets to achieve the desired properties. The thickness and grain orientation are carefully controlled during the manufacturing process to optimize the magnetic behavior. Compared with hot-rolled silicon steel, cold-rolled silicon steel has a uniform thickness, good surface quality, and high magnetic properties. Therefore, with the development of industry, cold-rolled silicon steel has gradually replaced hot-rolled silicon steel and become mainstream.
And according to its grain orientation, cold rolled silicon steel can be subdivided into non-oriented silicon steel and oriented silicon steel.
Cold Rolled Non-grain-oriented (NGO) Silicon Steel
Cold rolled non-grain-oriented silicon steel, usually contains a level of 2%-3.5% silicon. It has similar magnetic properties in all directions, the so-called isotropy.
Therefore, cold-rolled non-grain-oriented steel (CRNGO) is less expensive than cold-rolled grain-oriented steel (CRGO). CRNGO can be used in cost-oriented applications with the inconstant direction of magnetic flux, such as electric motors and generators. CRGO is usually in coil form and has to be cut into laminations further, being used in transformer core applications, such as certain internal parts in audio output transformers.
Cold Rolled Grain-oriented (GO) Silicon Steel
As the name suggests, cold rolled oriented silicon steel contains a level of 3% silicon and is processed in a way (parallel to the rolling direction) to develop ideal properties in the rolling direction.
Compared with cold rolled non-oriented silicon steel, the magnetism of oriented silicon steel has strong directionality. So it has superior high magnetic permeability and low loss characteristics in the rolling direction where magnetization is easy, complying with the magnetic permeability requirements of static power equipment such as transformers. In addition, under the same capacity, the volume and weight of the transformer core made of oriented silicon steel are reduced, which can save silicon steel, electromagnetic wires, and insulation materials.
What’s more, oriented silicon steel will be evaluated through magnetic testing after production. When the magnetic induction is less than 1.88T, it can be further subdivided into regular silicon steel (RGO); when the magnetic induction is greater than 1.88T, it can be further subdivided into high permeability-oriented silicon steel (HGO).
In terms of its detailed applications, it can be grouped into:
Motor silicon steel: Mainly used to fabricate motor.
Transformer silicon steel: Mainly used to manufacture transformer core.
In the steel market, silicon steel is commonly produced and sold in coil, sheet, and strip shapes, like:
Silicon steel is mainly smelted in an oxygen converter (an electric arc furnace can also be used), combined with vacuum treatment of molten steel and AOD technology. It usually uses die casting or continuous casting. Depending on the purpose, the silicon (0.5-4.5%) and aluminum (0.2-0.5%) content will be changed during smelting to meet different magnetic requirements. Below is a general process of silicon steel manufacturing process:
Ore preparation — smelting — casting — slab heating — rolling — normalizing — pickling — rolling — annealing — insulting coating
Silicon steel exhibits several important properties that make it suitable for usage. They are:
1. High Magnetic Permeability. Silicon steel has high magnetic permeability, which means it can easily conduct magnetic flux. This property is crucial for the efficient operation of motors and transformers.
2. Low Core Loss. Silicon steel has a low core loss, which refers to the energy dissipated as heat when an alternating magnetic field is applied. Low core loss helps to minimize energy losses in electrical devices.
3. High Electrical Resistivity. In comparison to iron, silicon steel shows a significant increase in resistivity, up to 5 times. This change results in a decrease in the alloy’s eddy current losses, hence improving energy efficiency.
Increased electrical resistivity, therefore, helps to improve its magnetic characteristics, reduce eddy current losses, and increase permeability.
4. Elegant Surface. Silicon steel is smooth in surface and uniform in thickness, helpful in improving the lamination coefficient of the iron core. A high lamination coefficient can increase the effective utilization of space in the iron core, reduce the air gap, and reduce the excitation current. For example, a 1% decrease in the lamination coefficient of silicon steel is equivalent to a 2% increase in iron loss and a 1% decrease in magnetic induction.
5. Low Magnetic Aging. When the carbon and nitrogen content in the silicon steel is less than 0.0035%, the magnetic aging effect is significantly reduced.
5. Certain Plasticity. To meet the needs of punching and shearing when manufacturing electrical appliances, silicon steel is also required to have a certain degree of plasticity. This is very important for manufacturing micro and small motors.
7. Low Iron Loss. Low iron loss is the most important indicator of the quality of silicon steel. It can save a lot of electricity, which extends motor and transformer operating time and simplifies the cooling system. Besides, countries around the world classify silicon steel grades according to the iron loss value. The lower the iron loss, the higher the grade and the higher the quality.
8. Excellent Insulating Film Performance. To prevent short circuits between core laminations and increase eddy current losses, the surface of silicon steel is usually coated with a thin layer of inorganic salt or a semi-organic insulation film of inorganic salt + organic salt. On the other hand, it can prevent corrosion and improve film processing properties.
As an essential soft magnetic material, silicon steel has established itself as a key player in contemporary industrial applications. Ranging from small-scale operations in relays and pulse transformers to large-scale use in generators, motors, and transformers, silicon steel continues to grow in importance. Its adoption has been driven by the need for more efficient energy use and the miniaturization of powerful equipment. Its main applications include:
1. Transformers: silicon steel is commonly used in the cores of power transformers. The low core loss and high magnetic permeability of silicon steel help to improve the efficiency of energy transfer from one voltage level to another in transformers. By using silicon steel cores, transformers can operate with high efficiency and minimize energy wastage.
2. Motors: silicon steel is also used in the construction of electric stators and rotor cores. Its magnetic properties reduce energy losses caused by magnetic hysteresis and eddy currents, allowing for efficient conversion of electrical energy into mechanical energy.
3. Inductors: silicon steel is used in the construction of inductors and chokes, which are passive electronic components that store and release energy in the form of magnetic fields.
Overall, silicon steel plays a crucial role in maximizing the efficiency and performance of various electrical devices. Its unique magnetic properties make it an indispensable material in the power, electronics, and military industries, contributing to improving efficiency and reducing energy consumption of electrical equipment.
In China, the grade of silicon steel is usually composed of number + English letter + number.
The first number indicates the thickness of steel (number/100); the letter indicates orientation or non-orientation (orientation=Q, non-orientation=W); while the last number indicates the iron loss (number/100). For example:
Oriented silicon steel: 30Q120, 30Q130, 30Q140…
Non-oriented silicon steel: 50W470, 50W600…
In conclusion, silicon steel is an integral part of modern industries, playing a key role in various applications. It can increase resistivity, reduce hysteresis losses, increase permeability, and virtually eliminate aging. These unique properties make it an irreplaceable component in the generation, distribution, and consumption of transformers, motors, inductors, and other electrical apparatus. With continuous research and development, better forms of silicon steel are anticipated, further revolutionizing the industrial landscape!
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