ब्लॉग

Silicon steel, scientifically known as Fe-Si soft magnetic alloy and also referred to as electrical steel, has a silicon content ranging from 0.5% to 6.5%. It resembles iron sheets as thin as cicada wings but with excellent “memory”, capable of being repeatedly magnetized in an alternating magnetic field without easily heating up. Its three trump cards – high magnetic permeability, low iron loss, and high saturation magnetic induction intensity – make it the “unique choice” for the iron cores of motors, transformers, and generators. Without it, the power grid cannot efficiently transmit every kilowatt-hour of electricity; without it, variable frequency air conditioners, new energy vehicles, and wind turbines would all “pant like a bull”.

02 A Century of Journey – Silicon Steel Technology Roadmap

2.1 ◇ Hot-rolled era: The first leap from low-carbon steel to silicon steel In 1886, Westinghouse in the United States used low-carbon steel plates with 0.4% carbon content as transformer cores, resulting in significant eddy current losses and severe magnetic aging. In 1902, Gumlich of Germany discovered that by adding a small amount of silicon, the resistivity soared, losses plummeted, and magnetic aging was reduced. Hot-rolled silicon steel thus entered the historical stage. Within just a few years, it replaced low-carbon steel and became the “mainstay” of motors and transformers.

2.2 ◇ Cold Rolling Era: The “Unique Skill” of Oriented Silicon Steel In 1933, Gauss used two rounds of cold rolling and annealing to maximize the magnetic properties of 3% Si steel along the rolling direction. In 1953, Japan’s Nippon Steel took a further step by inserting AIN+MnS dual inhibitors into cold-rolled strips. In 1964, they launched “Hi-B” high magnetic induction oriented silicon steel, which pushed Japanese electrical steel to the world’s peak. Cold-rolled non-oriented silicon steel, with its advantages of high thickness precision, smooth surface, and low magnetic anisotropy, continues to play a supporting role in small motors.

2.3 ◇ China’s trajectory: From following to paralleling. In 1952, Taiyuan Iron and Steel Plant took the lead in trial-producing hot-rolled low silicon steel. In 1974, Wuhan Iron and Steel introduced the Japanese Hi-B patent, and in 1979, domestically produced Hi-B rolled off the production line, which remains the “ballast” for domestic oriented silicon steel to this day. Nowadays, Wuhan Iron and Steel, Baosteel, and Shougang form a tripartite confrontation, with high-end oriented silicon steel being exported in bulk. Electrical steel made in China has accounted for half of the global market share.

03 Classification and Application – Understanding “Who Should Use Whom” with a Single Diagram

3.1 ◇ Low-silicon electrical steel (Si<0.5%) by silicon content: suitable for household small appliances with low electromagnetic performance requirements, featuring simple process, low cost, and almost “the same process” as plain carbon steel.

Medium silicon electrical steel (0.5%<Si<4.5%): the main material for motor and transformer cores, with multiple grades and a complex system.

High silicon electrical steel (4.5%<Si≤6.5%): “exclusive” for high-frequency motors, choke coils, and magnetic shielding. It has poor room temperature plasticity and can only be processed into thin strips through siliconizing technology at present.

3.2 ◇ Hot-rolled electrical steel categorized by production method and crystal orientation: This type has been nearly phased out and is only used for low-end laminations.

Cold-rolled non-oriented: 0.65–0.35 mm thickness, low magnetic anisotropy, high punching coefficient, widely used in various motors.

Cold-rolled single orientation (Goss): grains are easily magnetized along the rolling direction, with a deviation angle of 7° for CGO steel and B8 ≈ 1.82 T; for Hi-B steel, the deviation angle is 3°, and B8 ≈ 1.90 T. It is specifically used for large transformers and choke coils.

Cold-rolled dual orientation (cubic): a laboratory concept, not yet industrialized.

Figure 2 illustrates the global map of silicon steel applications: transformers stand out, followed closely by motors, and high-frequency devices are in the ascendant.

04 Performance indicators – iron loss and magnetic induction are “hard currency”

4.1 ◇ Iron loss P: The “heat funnel” iron loss in an alternating magnetic field = hysteresis loss Ph + eddy current loss Pe + anomalous loss Pa.

Non-oriented silicon steel: Ph accounts for the majority, and P1.5/50 is the core of assessment.

Grain-oriented silicon steel: Permeability (Pe) prevails, and P1.7/50 directly determines the temperature rise and no-load loss of transformers.

4.2 ◇ Magnetic induction intensity B: It determines how much magnetic field the iron core can accommodate. Increasing Bm can reduce the cross-sectional area of the iron core, decrease the weight of copper wire, and reduce the excitation current. For non-oriented materials, B50 (5 kA/m) is used, while for oriented materials, B8 (T) is used. The higher the value, the more “expensive” it is.

4.3 ◇ Additional requirements: The difference in iron loss between the longitudinal and transverse directions should be ≤8%, and the difference in magnetic induction should be ≤10%, ensuring consistent performance after lamination.

Only by fully optimizing the hot-rolled plate shape, cold-rolled roughness, and insulation coating quality can we produce a “dual-high” product with low iron loss and high magnetic induction.

05 Grade representation method – understand the “numerical code” at a glance

Figure 3 breaks down the grade rules for domestic non-oriented and oriented silicon steel into three lines of code: material code + serial number + application code, which is simple and easy to remember.

06 Future Direction – Thinner, Lower, More Efficient

Thin-gauge low-iron-loss non-oriented silicon steel: Cutting it by an additional 0.35 mm can reduce iron loss by another 10%, potentially increasing motor efficiency by 2–3 percentage points.

Ultra-low core loss Hi-B oriented silicon steel: Nippon Steel has been able to stably supply steel with a thickness of 0.15–0.35 mm. Japan Steel Tube Corporation has produced high-silicon thin strips using CVD siliconizing, and Chinese manufacturers are catching up.

High-silicon steel for medium and high-frequency energy-saving appliances: The “magic content” of 6.5% Si still shines and generates heat at high frequencies, and new energy vehicle motors and marine propulsion systems are becoming new battlegrounds.

Next-generation revolutionary technology: nanocrystalline, amorphous and silicon steel composites, ultra-fast cooling (USAB) + nanometer inhibitors, potentially ushering in a new era where iron loss is reduced to below P17/50.

As the power grid transitions towards being green, efficient, and distributed, every kilowatt-hour of electricity must be accounted for and conserved. Silicon steel, serving as the “brain” of motors and transformers, is addressing the most pressing question of the era from a material perspective: how to make steel smarter? The answer may lie in thinner strips, lower iron loss, and higher magnetic induction—these are the starting points for the next energy revolution.