Electrical Steel Sheet (Dynamo and Transformer Steel): Characteristics, Grades, and Applications

Electrical Steel Sheet (Electrical Steel) — is a specialized soft magnetic iron-silicon alloy designed for use in electromagnetic fields. The primary goal of this material is to efficiently conduct magnetic flux while minimizing energy losses due to dissipation and heating.

The efficiency (КПД) of any electrical equipment directly depends on the quality of electrical steel products: from tiny stepper motors in smartphones to giant turbogenerators in hydroelectric power plants.

Classification of Electrical Steels

In global metallurgy, all electrical steel sheet products are divided into two fundamental classes based on their internal crystal lattice:

1. Dynamo (Isotropic / Non-Oriented) Steel. This material exhibits nearly identical magnetic properties in all directions within the sheet plane. It is used where the magnetization vector constantly changes its angle: in rotating electrical machines (rotors and stators of electric motors, generators). Manufactured according to GOST 21427.2.
2. Transformer (Anisotropic / Grain-Oriented) Steel. It undergoes complex texturing rolling, which aligns the silicon ferrite grains strictly along the rolling direction. The magnetic permeability along the sheet is several times higher than across it. It is used in static devices (power, pulse, and measuring transformers). Manufactured according to GOST 21427.1.

Influence of Chemical Composition on Process Physics

The key alloying element of the alloy is silicon ($Si$), the content of which varies from 0.5% to 4.5%.

Introducing silicon solves a critical physical problem: it sharply increases the electrical resistivity of ferrite. When an alternating magnetic field penetrates the magnetic core, parasitic eddy currents (Foucault currents), which heat the metal. The high resistance of silicon steel inhibits these currents, reducing heat losses.

However, the metallurgical process has a strict limitation: at silicon concentrations above 4%, the steel becomes brittle, which makes its cold rolling and fine stamping an extremely difficult task. The content of carbon ($C$) in the finished sheet is reduced to an absolute minimum (less than 0.005%) to eliminate the effect of "magnetic aging" — the degradation of properties over time.

Key Electromagnetic Characteristics

When designing magnetic cores, engineers rely on three basic parameters of electrical steel sheets:

• Specific magnetic losses ($P_{1.5/50}$ or $P_{1.7/50}$). They show how many Watts of energy are lost per 1 kg of steel at a magnetic induction of 1.5 or 1.7 T and a current frequency of 50 Hz. The lower the number, the higher the energy efficiency class of the product.
• Magnetic induction ($B_{50}$). The ability of a metal to become saturated by a magnetic field at a given field strength.
• Stacking factor. It determines how tightly the laminations fit together in an assembled stack. It is influenced by the flatness of the rolled product and the thickness of the insulating layer.

Russian Grades and International Equivalents

Purchasers and design bureaus often face the need to convert foreign specifications to domestic standards. The main correspondence tables are as follows:

Dynamo Steel (Isotropic)

Grade according to GOST 21427.2 EN 10106 Standard (Europe) ASTM A677 Standard (USA) Typical Application 2013, 2212M600-50A / M700-65A M-43 / M-47 Household appliance motors, chokes 2412, 2414 M400-50AM-36 Industrial Induction Motors

Transformer Steel (Anisotropic)

Grade according to GOST 21427.1 EN 10107 Standard (Europe) ASTM A876 Standard (USA) Typical Application3411, 3413 M140-30S / M150-35SM-5 Oil-immersed and Dry-type Power Transformers 3404, 3405 M130-27SM-4 High-frequency and Measuring Devices

Note on GOST marking: the first digit '2' indicates isotropic steel, '3' indicates anisotropic; the second digit is the silicon content percentage (e.g., '4' = 2.8 to 3.8%).

Processing and Electrical Insulation Characteristics

To prevent the core assembled from sheets from acting as a single monolithic conductor, the plates must be electrically insulated from each other. Electrical steel sheets are supplied with special coatings:

1. Organic (varnish-based). Easily stamped, but can only withstand heating up to 150–180°C.
2. Semi-organic and inorganic (ceramic). Withstand annealing temperatures up to 850°C and are resistant to immersion in transformer oil.

Due to the increased hardness of silicon steel, stamping plates with complex geometries leads to accelerated wear of punches. For experimental batches and high-precision devices, laser cutting is used, followed by edge stress relief by short-term low-temperature annealing.

Electrical Steel Products at PZPS Production Facility

Petersburg Plant of Precision Alloys (PZPS) supplies cold-rolled sheet and strip products with strictly controlled geometric and magnetic tolerances.

Advantages of working with PZPS:

• Precision Geometry: thickness variation of the rolled product is minimized to micron values, ensuring perfect assembly of the magnetic core stack without air gaps.
• Custom Tolerances: ability to produce strip of non-standard width and thickness (down to the thinnest foil sections).
• Laboratory Control: our own Central Factory Laboratory (CFL) checks each batch for compliance with declared magnetization curves and specific loss levels.

For technical consultation, to order free samples, or to calculate the cost of a batch of electrical steel according to your technical specifications, please contact the PZPS sales department via the feedback form below or by phone.

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