Electrical steel: production and application

2024 Author: Howard Calhoun | [email protected]. Last modified: 2023-12-17 10:16

The production of this type of steel occupies a leading position among other magnetic materials. Electrical steel is an alloy of iron with silicon, the proportion of which ranges from 0.5% to 5%. The wide popularity of products of this type can be explained by high electromagnetic and mechanical properties. Such steel is made from widely used components, in which there is no shortage. This explains its low cost.

Influence of silicon

This component, in interaction with iron, forms a dense solution with high resistivity, the value of which depends on the percentage of silicon in the alloy. When exposed to pure iron, it loses its magnetic properties.

But when it affects the technical, on the contrary, it has a positive effect. The permeability of iron increases and the stability of the metal improves. The favorable effect of silicon (Si) can be explained as follows. Under the influence of this element, carbon is transferred to graphite from the state of cementite, which has less magnetic properties. The element Si has an undesirable effect ondecrease in induction. Its influence extends to thermal conductivity and to the density of iron.

Impurities in composition

In its composition, electrical steel may contain other components: sulfur, carbon, manganese, phosphorus and others. The most harmful of them is carbon (C). It can be in the form of both cementite and graphite. This affects the alloy differently, as does the percentage of carbon. To avoid unwanted inclusions of element C, the steel must not be rapidly cooled for the next aging and stabilization.

The following components have a negative impact on the properties of the material: oxygen, sulfur, manganese. They reduce its magnetic qualities. Technical iron in its composition necessarily has impurities. Here they have to be taken into account in the aggregate, not in the same way as for pure iron.

You can improve the properties of steel by removing impurities. But this method is not always beneficial in large-scale production. But with the help of cold rolling, sheet electrical steel forms magnetic properties in its structure. This allows you to achieve the best results. But further firing is required.

Cold rolling

Silicon has long been thought to increase the brittleness of steel. The production took place mainly by means of hot rolling. Profitability of cold rolling was low.

Only after it was discovered that cold working along the direction of the material increases the magnetic properties, it has been widely used. Other directions showed themselves only withthe worst side. Cold rolling has a beneficial effect on the mechanical properties, as well as improving the quality of the sheet surface, increasing its waviness and making it possible to stamp.

The distinctive properties that electrical steel received through the use of cold working can be explained by the formation of a crystallographic texture in it. It differs in several degrees. They, in turn, depend on the temperature at which the rolling takes place, as well as on the thickness of the required sheet and on the degree to which it is reduced.

The cost of a sheet of one thickness of hot-rolled steel is 2 times lower than that of cold-rolled steel.

But this negative quality is fully compensated by low heat losses (there are less than about two times), high quality and the possibility of good stamping of cold-rolled alloy. The difference in these steels is the silicon content. Its amount is from 3.3% to 4.5% respectively.

GOST

Manufacturers produce only two types of steel that comply with GOST.

First view - 802-58 "Electrotechnical sheet". The second one is electrical steel GOST 9925-61 "Cold-rolled coiled strip made of electrical steel".

Designation

Marked with the letter "E", followed by a number whose digits have a specific meaning:

• The first digit in the marking value means the degree of alloying of steel with silicon. From low-alloyed to high-alloyed, respectively, in numbers from 1 to 4. Dynamic - these are steels from groups E1 and E2. Transformer - E3 and E4.
• The second digit of the marking has a range from 1 to 8. It shows the electromagnetic properties of the material when used in certain operating conditions. By this marking, you can find out in which areas this or that steel can be used.

The number zero following the second number means that the steel is textured. If there are two zeros, then it is not textured enough.

At the end of the marking you can find the following letters:

• "A" - very low specific material loss.
• "P" is a material with high rolling strength and high surface finish.

Operating area

The alloy is divided into three types according to the field of application:

• suitable for work in strong and medium magnetic fields (remagnetization purity 50 Hz);
• suitable for working in medium fields up to 400Hz;
• steel that is operated in medium and low magnetic fields.

Sheets of electrical steel are produced in the following sizes: width from 240 to 1000 mm, length can be from 720 mm to 2000 mm, thickness - in the range from 0.1 to 1 mm. Most of all, grain-oriented steels are used, as they have a high value of electromagnetic properties. Sheets of this material are often used in electrical engineering.

Electrical steel - properties

Alloy properties:

• Resistivity. The quality of the material directly depends on this indicator. Steel is used where it is necessary to contain electricity inside the conductor and deliver it to its destination.
• Coercive force. Responsible for the ability of the internal magnetic field to demagnetize. For certain devices, this property is required to varying degrees. In transformers and electric motors, parts with a high demagnetization capacity are used. For steel, this indicator has a low value. But in electromagnets, on the contrary, a high coercive force is needed. To correct the magnetic properties, the required percentage of silicon is added to the steel alloy.

• The width of the hysteresis loop. This indicator should be as low as possible.
• Magnetic permeability. The higher this indicator, the better the material "does" with its tasks.
• The thickness of the sheet. For the manufacture of many devices and parts, materials are used whose thickness does not exceed one millimeter. However, if necessary, this indicator is reduced to a value of 0.1 mm.

Application

First class sheet materials can be used to make different types of magnetic circuits for relays and regulators.

Second grade electrical steel can be used for AC and DC starters, rotor cores.

The third class will be suitable for the manufacture of magnetic circuits forpower transformers, as well as starters of large synchronous machines.

To make a frame for an electric machine, you need to use steel casting, in which the carbon content is not more than 1%. Products made from such material are subjected to gradual annealing. Carbon steel is used in the manufacture of machine parts that are welded.

Main poles for DC machines are made from these types of materials.

For those machine parts that carry the maximum load (springs, rotors, armature shafts), alloys with high mechanical properties are used. Such material may contain nickel, chromium, molybdenum and tungsten. It is possible to manufacture magnetic circuits from electrical steel. They are used for low frequency transformers - 50Hz.

Stand magnetic circuit

Magnetic cores are divided into armor and rod. Each species has its own characteristics.

Rod: for such a magnetic circuit, the rod is vertical and has a stepped section inscribed in a circle. The windings of the magnetic circuit are located on them in a special cylindrical shape.

Armored

Products of this design are rectangular in shape, and their rods have a cross section, they are located horizontally. This type of magnetic circuit is used only in complex devices and structures. Therefore, such designs are not widely used.

So we figured out what steel iselectrical and where it is used.