The production of this type of steel occupies a leading position among other magnetic materials. Electrotechnical steel is an alloy of iron with silicon, the proportion of which is 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 widespread components, in which there is no shortage. This explains its low cost.
Silicon effect
This component in interaction with iron forms a dense solution with high resistivity, the value of which depends on what 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 beneficial effect of silicon (Si) can be explained as follows. Under the influence of this element, carbon transitions to graphite from the state of cementite, which has less magnetic properties. The Si element has an undesirable effect on reducing induction. Its influence extends to thermal conductivity and to the density of iron.
Impurities in the 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 in different ways, as does the percentage of carbon. In order to avoid unwanted inclusions of element C, it is impossible to cool the steel quickly for the next aging and stabilization.
The following components have a negative effect on the material properties: oxygen, sulfur, manganese. They reduce its magnetic properties. Technical iron necessarily contains impurities. Here they have to be taken into account in the aggregate, not like for pure iron.
The properties of steel can be improved by applying impurities. But such a method is not always advantageous 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 better results. But further firing is necessary.
Cold rolling
For a long time, it was believed that silicon increases the brittleness of steel. Production took place mainly with the help of hot rolling. Profitability of cold rolling was low.
Only after it was discovered that cold working along the direction increases the magnetic properties of the material, it was widely used. Other directions have shown themselves only from the worst side. Cold rolling beneficially affected the mechanical properties, as well as improving the quality of the sheet surface, increased its waviness and made it possible to stamp.
The distinctive properties obtained by electrical steel due to the use of cold processing 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, also on the thickness of the required sheet and on the extent to which it is crimped.
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 completely compensated by low heat losses (there are less than about half of them), high quality and the possibility of good stamping of a 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.
The first type is 802-58 "Electrotechnical thin-sheet". The second is electrical steel GOST 9925–61, “Cold rolled coil tape made of electrical steel”.
Designation
It is marked with the letter “E”, followed by a number, the numbers of which have a certain meaning:
- The first digit in the marking value indicates the degree of alloying of steel with silicon. From lightly alloyed to highly alloyed, respectively, in numbers from 1 to 4. Dynamo - this is steel 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 applied under certain operating conditions. By this marking you can find out in which areas this or that steel can be used.
The number zero after the second number means that the steel is textured. If there are two zeros, then it is slightly textured.
At the end of the marking, you can see the following letters:
- "A" - the specific loss of material is very low.
- "P" - a material with high strength rolled and high surface finish.
Field of operation
The alloy is divided into three types according to its field of application:
- suitable for work in strong and medium magnetic fields (magnetization reversal purity 50 Hz);
- suitable for work in medium fields at a frequency of up to 400 Hz;
- steel, which 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. Textured steels are most widely used, since they have a high value of electromagnetic properties. Sheets of such 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 restrain electricity inside the conductor and deliver it to its intended purpose.
- Coercive force. Responsible for the ability of the internal magnetic field to demagnetize. For certain devices, this property is required to varying degrees. Transformers and electric motors use parts with a high demagnetization ability. In steel, this indicator is low. But in electromagnets, on the contrary, a high coercive force is needed. To adjust the magnetic properties, the desired percentage of silicon is added to the steel alloy.
- Hysteresis loop width. This indicator should be as low as possible.
- Magnetic permeability. The higher this indicator, the better the material "copes" with its tasks.
- Sheet thickness. For the manufacture of many devices and parts using materials whose thickness does not exceed one millimeter. However, if necessary, this indicator is reduced to a value of 0.1 mm.
Application
Different types of magnetic cores for relays and regulators can be made from sheet materials of the first class.
Electrotechnical steel of the second class grade can be used for starters of direct and alternating current electric machines, rotor cores.
The third class will be suitable for the manufacture of magnetic cores for power transformers, as well as starters for large synchronous machines.
To make a skeleton for an electric machine, it is necessary to apply steel casting, in which the carbon content is not more than 1%. Products from such a material are subjected to gradual annealing. Carbon steel is used in the manufacture of parts of machines undergoing welding.
Of these types of materials make the main poles for DC machines.
For those machine parts that carry the maximum load (springs, rotors, anchor shafts), alloys with high mechanical properties are used. Such material may contain nickel, chromium, molybdenum and tungsten. It is possible to make magnetic cores from electrical steel. They are used for low frequency transformers - 50Hz.
Core magnetic core
Magnetic cores they are divided into armored and rod. Each species has its own characteristics.
Rod: in such a magnetic core, the rod is vertical and has a step 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 have a rectangular 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 found out what electrical steel is and where it is used.