What is electrical steel?

What is Silicon Steel?

Silicon steel refers to the Fe-Si soft magnetic alloy, also known as electrical steel. The mass percentage of silicon (Si) in silicon steel ranges from 0.4% to 6.5%. It is characterized by high magnetic permeability and low core loss, offering excellent magnetic properties such as low iron core loss, high magnetic induction strength, good punching quality, high-quality steel plate surfaces, and effective insulating film coatings. Silicon steel is primarily used in the preparation of cores for various electrical equipment, including motors, generators, and transformers. It is an indispensable metal functional material in the power, electronics, and military industries and is a key material for improving the efficiency and reducing energy consumption of power equipment. As the soft magnetic alloy with the largest volume, electrical steel is extensively used in all sectors of the real economy. Enhancing its overall performance and manufacturing level plays a very important role and holds significant meaning for the development of the national economy.

The Nature of Electromagnetic Conversion

Electromagnetic induction refers to the phenomenon where an electromotive force (EMF) is generated in a conductor when it moves through a magnetic field or when the magnetic field changes. According to Faraday's law of electromagnetic induction, when a conductor cuts through magnetic field lines, an EMF is produced at the ends of the conductor, which can generate an electric current in a closed circuit. Conversely, if an electric current passes through a conductor, it produces a force in the magnetic field, causing the conductor to move, thus converting electrical energy into mechanical energy.

Applications of Electromagnetic Conversion

This principle is widely applied in many electrical devices and machines, such as generators, motors, and transformers. For instance, a generator uses the rotation of conductors in a magnetic field to generate EMF, converting mechanical energy into electrical energy. On the other hand, an electric motor uses the force produced by the current in a magnetic field to rotate the rotor, converting electrical energy into mechanical energy.

‍The Value of Electrical Steel in Electromagnetic Conversion

Electrical steel, also known as silicon steel or electromagnetic steel, is a special type of steel characterized by high magnetic permeability and low hysteresis loss, making it highly suitable for electromagnetic devices. The role of electrical steel in electromagnetic induction is mainly reflected in the following aspects:

• Reducing hysteresis loss: Electrical steel has low hysteresis loss, which means that less electrical energy is converted into heat during the process of repeated magnetization and demagnetization. This is crucial for improving the efficiency of electromagnetic devices.
• Enhancing magnetic permeability: Electrical steel has high magnetic permeability, making it easier to magnetize and effectively conduct magnetic fields. This helps establish and maintain strong magnetic fields in electromagnetic devices.
• Reducing eddy current losses: Electrical steel typically has a thin laminated structure with an insulating coating, which helps reduce eddy currents (circulating currents in conductors that cause energy loss). In devices like motors and transformers, reducing eddy current losses can improve overall efficiency.
• Stabilizing magnetic fields: In generators and transformers, electrical steel sheets are stacked to form a core that shapes the magnetic path. This ensures efficient transmission of the magnetic field within the device, reducing energy loss.

The Development History of Silicon Steel

Before the advent of silicon steel, cores were traditionally made from industrial pure iron. In 1886, the American Westinghouse Electric Corporation used hot-rolled low-carbon steel plates with an impurity content of about 0.4% to fabricate transformer laminated cores. However, the low resistivity of low-carbon steel resulted in high core losses, high carbon and nitrogen content, and severe magnetic aging. In 1902, Gumlich of Germany discovered that adding silicon could increase iron's resistivity, reduce eddy current and hysteresis losses, enhance permeability, and alleviate magnetic aging phenomena.

From 1882 to 1995, it was primarily the development stage of hot-rolled silicon steel. In 1903, the United States and Germany initiated the production of hot-rolled silicon steel. By 1905, the United States (followed by the United Kingdom in 1906) had begun mass production, and in a short span, it completely replaced ordinary low-carbon steel plates in the manufacturing of motors and transformers. Due to the superior magnetic induction, core loss, cutting processability, surface quality, and insulating coating quality of cold-rolled non-oriented silicon steel, along with the inability of hot-rolled products to be produced in rolls, reducing punching efficiency, the main industrialized countries gradually ceased the production of hot-rolled silicon steel in the 1960s.

From 1930 to 1967, it was mainly the development stage of cold-rolled ordinary grain-oriented silicon steel (CGO) plates. In 1933, Gauss utilized a double cold-rolling and annealing method to produce 3% Si steel with high magnetic properties along the rolling direction. In 1935, the American Armco Steel Corporation, leveraging Gauss's patent technology in collaboration with Westinghouse, commenced the production of cold-rolled grain-oriented silicon steel. After two decades of continuous development, Armco perfected the double cold-rolling grain-oriented silicon steel production process, known as the Armco process, in the mid-1950s. Since then, the Armco process has dominated the world's cold-rolled grain-oriented silicon steel production, with approximately 80% of ordinary grain-oriented silicon steel (CGO) output being manufactured according to the Armco patent.

From 1961 to 1994, it was primarily the development stage of high magnetic induction grain-oriented silicon steel (Hi-B). In 1953, Tanaka Satoru of Nippon Steel Corporation in Japan demonstrated that using AlN as the main inhibitor and employing a large reduction cold-rolling process could yield higher magnetic grain-oriented silicon steel. In 1961, based on the Armco patent, the first trial production of high magnetic induction grain-oriented silicon steel with AlN+MnS composite inhibitors was initiated. Production began in 1964 and was named Hi-B, although the magnetic properties were initially unstable. Since Nippon Steel developed high magnetic induction grain-oriented silicon steel products in 1968, Japan's cold-rolled electrical steel has surpassed the United States in terms of product quality, manufacturing technology and equipment, new technology development, experimental research, and testing technology, securing an absolute leading position globally.

China first trial-produced hot-rolled low silicon steel plates (1% to 2% Si) in 1952 and officially commenced production in 1954. In 1957, the Chinese Academy of Steel Research successfully developed 3% Si cold-rolled grain-oriented silicon steel. In 1974, Wuhan Iron and Steel Corporation introduced cold-rolled grain-oriented silicon steel manufacturing equipment and patents from Nippon Steel in Japan. Between 1976 and 1977, the Steel Research Institute developed Hi-B grain-oriented silicon steel based on the verification and assimilation of Japanese patents. In 1979, Wuhan Steel officially began producing grain-oriented silicon steel and remains one of China's main production bases for grain-oriented silicon steel to this day.

Oriented Electrical Steel:

• Material Characteristics: Oriented electrical steel is highly anisotropic, meaning its magnetic properties in one direction are significantly better than in others. This steel has extremely high magnetic permeability and low hysteresis loss in the direction of grain orientation.
• Manufacturing Process: During the production of oriented electrical steel, the steel's grains are treated to ensure a high degree of alignment in the plane of the sheet. This treatment gives the steel its best magnetic properties in a specific direction.
• Application Scenarios: Due to its high magnetic permeability and low hysteresis loss, oriented electrical steel is mainly used in applications that require high efficiency and high magnetic permeability, such as the cores of transformers and reactors.

Non-oriented Electrical Steel:

• Material Characteristics: Non-oriented electrical steel does not exhibit significant anisotropy, meaning its magnetic properties are relatively uniform in all directions. This steel has average magnetic permeability and hysteresis loss in all directions.
• Manufacturing Process: In the production of non-oriented electrical steel, the grains are not treated for orientation, resulting in consistent magnetic properties in all directions.
• Application Scenarios: Due to its uniform magnetic properties, non-oriented electrical steel is suitable for applications that require good magnetic properties in multiple directions, such as the cores of rotating machines (like motors and generators).

In summary, the difference between oriented and non-oriented electrical steel lies primarily in the orientation of the grains and the anisotropy of magnetic properties. These differences lead to their suitability for different electromagnetic application scenarios. Oriented electrical steel is suitable for unidirectional magnetic field applications, such as transformers, while non-oriented electrical steel is suitable for multidirectional magnetic field applications, such as motors and generators.

Classification and Applications of Silicon Steel

Silicon Mass Fraction

Silicon steel is categorized based on the silicon mass fraction into two types: electrical steel with Si less than 0.5% and silicon steel with 0.5% to 4.5% Si. Both are collectively referred to as electrical steel plates. The former is widely used in the manufacturing of civilian small appliances where electromagnetic performance requirements are not high. This type of silicon steel sheet is characterized by a significantly lower silicon content compared to conventional electrical steel, a simple preparation process, and lower costs, similar to those of ordinary carbon steel. The latter encompasses a complex variety of types and grades.

High silicon steel denotes Si-Fe alloys containing 4.5% to 6.7% Si. It features significantly reduced iron loss at high frequencies, high maximum magnetic permeability, low coercivity, and superior magnetic properties. It is primarily utilized in the manufacturing of high-frequency motors, high-frequency transformers, choke coils, and high-frequency magnetic shielding. However, due to the high silicon content, it has extremely poor plasticity at room temperature and cannot be rolled into shape. 6.5% Si forms its own category due to its unique magnetic properties. Currently, only a limited amount of non-oriented 6.5% Si-Fe alloy materials prepared by the silicon infiltration process are available in rolls, and the preparation of more performance-advantaged oriented 6.5% Si-Fe alloys is even more challenging.

Production Process

Silicon steel can be divided into hot-rolled and cold-rolled electrical steel based on the production method. Hot-rolled silicon steel plates have been gradually phased out in recent years due to their outdated performance. The most widely accepted method of categorizing silicon steel is based on the degree of crystal orientation aggregation into non-oriented and oriented types. Cold-rolled non-oriented silicon steel refers to an alloy containing 0.5% to 4.0% (Si+Al), which is cold-rolled to thicknesses of 0.65mm, 0.5mm, and 0.35mm, and then manufactured after annealing and coating. Compared with oriented silicon steel, it has a more scattered grain texture, more uniform magnetic properties in all directions, and lower magnetic anisotropy, mainly used as laminated cores for various types of motors and generators. The thickness precision, dimensional tolerance grade, and surface smoothness of cold-rolled products have reached high standards, thereby improving the lamination coefficient and magnetic performance of the material. Oriented silicon steel exhibits high magnetic permeability and low loss characteristics in the direction of easy magnetization, meeting the magnetic guidance requirements for static power equipment such as transformers, and is primarily used in the manufacturing of various large transformers, chokes, and other high-end electromagnetic components in the power industry.

Performance Indicators of Silicon Steel

The laminated core of electrical steel and the copper wire operate through electromagnetic induction, with the core forming an alternating magnetic field. The core's own energy consumption and magnetization capability during operation determine the core performance of electrical equipment, including power, volume, efficiency, quality, and overall operating costs. Therefore, the performance indicators required for electrical steel include the following:

1) Core Loexcitation current, copper losses, and core losses, and improving the efficiency of energy transformation. Additionally, the total magnetization strength of the core is the product of its magnetic induction and area. Therefore, an increase in magnetic flux density (Bm) allows for a corresponding reduction in the cross-sectional area, which in turn reduces the mass of the core and copper wires, thereby lowering the electrical appliance's iron losses and costs. The guaranteed value for the magnetic induction of non-oriented silicon steel is taken as B50, which is the magnetic induction strength under a magnetic field of 5000 A/m, while for oriented silicon steel, the magnetic induction is taken as B8, with the unit of magnetic induction being Tesla. Different standards of magnetic flux density are adopted for different types of electrical steel.

These two indicators are closely related to the composition design, core process design, and control levels in the production process of electrical steel and are the most fundamental requirements for the performance of electrical steel. The precision of hot/cold rolling and the quality of the insulating coating are also essential conditions for high-quality electrical steel. Moreover, non-oriented electrical steel also requires magnetic anisotropy, meaning the difference in iron loss between the longitudinal and transverse directions should be ≤8%, and the difference in magnetic induction should be ≤10%.

Silicon Steel Grade Indication Method

The indication method for silicon steel grades is standardized to ensure clarity and consistency in the industry.

Domestic Electrical Steel Manufacturers and Market Insights

The production of electrical steel in China is primarily led by state-owned enterprises, with Baosteel and Shougang being the major players in the industry. As of 2020, Baosteel held a 28.42% share of the non-oriented electrical steel market, Shougang had 14.05%, and Taiyuan Iron & Steel had 11.53%. In the oriented electrical steel sector, Baosteel dominated with a 53.04% share, followed by Shougang.In the first half of 2023, China produced 7.2512 million tons of electrical steel, including 1.2295 million tons of oriented electrical steel, a year-on-year increase of 16.98%, and 6.0217 million tons of non-oriented electrical steel, a year-on-year increase of 7.23%.The main applications of electrical steel include new energy vehicles, ultra-high voltage projects, rail transit, large motors, smart home appliances, photovoltaic power generation, wind power, and the Internet of Things. Non-oriented electrical steel is primarily used for manufacturing magnetic materials in motors, transformers, electrical appliances, and electrical instruments, while oriented electrical steel is mainly used in the power transformer sector.The demand for electrical steel is closely related to the development of the power equipment industry. With the national emphasis on energy efficiency and environmental protection, the demand for high-performance electrical steel is expected to continue growing. In terms of sales, the market demand for electrical steel is closely related to the macroeconomy, industry policies, and technological development. Due to the high technical and capital barriers in the electrical steel industry, new entrants face certain challenges. Additionally, the quality certification process for electrical steel is strict, and establishing stable cooperative relationships with downstream customers is crucial for electrical steel manufacturers. Therefore, although there is competition in the electrical steel market, state-owned enterprises still dominate the high-end product sector.

Future of Silicon Steel

Over the past 20 years, China's silicon steel industry has made significant progress, with companies such as Shougang, Wuhan Iron and Steel (WISCO), and Baosteel leading the way. However, there is still a considerable gap compared to Japan in the field of high-end electrical steel, particularly in products like high magnetic induction non-oriented silicon steel, ultra-low iron loss Hi-B oriented silicon steel, and high silicon steel. For instance, Nippon Steel & Sumitomo Metal Corporation can stably supply a series of ultra-low iron loss Hi-B oriented electrical steel with thickness specifications ranging from 0.15 to 0.35 mm, leading the development of oriented silicon steel technology. In the field of special-purpose silicon steel, JFE of Japan has achieved the supply of high silicon steel thin strips through the chemical vapor deposition (CVD) silicon infiltration method. With the industrial upgrade of China's equipment manufacturing industry, the demand for high-end silicon steel products will become increasingly urgent. Competition in this field between China and steel powerhouses such as Japan and South Korea will become more intense. The future of the electrical steel industry includes low iron loss, high magnetic induction for efficient motors using non-oriented silicon steel, thin specification ultra-low iron loss high magnetic induction for oriented silicon steel, and high silicon steel for energy-saving electrical appliances in medium and high frequencies.

Baohui Steel Limited, as an authorized dealer of Baosteel, has a large inventory of hot-rolled steel and silicon steel products in stock. If you have any questions about the grades or performance of silicon steel, please contact us. We will have professional steel experts provide one-on-one assistance to you.