Silicon steel sheets, also known as ferrosilicon sheets, are an indispensable metal material in the power, electronics, and military industries.
Silicon steel sheets, also known as ferrosilicon sheets, are indispensable metallic materials in the power, electronics, and military industries. They belong to the category of low-carbon ferrosilicon soft magnetic alloys and are among the most produced functional metallic materials, accounting for approximately 1% of global steel production. This material contains 0.8% to 4.8% silicon and can be produced into silicon steel sheets with a thickness of less than 1 mm through hot rolling and cold rolling processes. The addition of silicon increases the resistivity and maximum permeability of iron while reducing coercivity, iron loss, and magnetic aging. Therefore, silicon steel sheets are widely used in the manufacture of cores for various motors, generators, and transformers. Based on the silicon content, silicon steel sheets can be divided into low-silicon and high-silicon categories.
1. Low-Silicon Wafers
Low-silicon wafers have a silicon content of less than 2.8% and possess a certain mechanical strength. These silicon steel sheets are primarily used in the manufacture of motors and are therefore also called motor silicon steel sheets.
2. High-Silicon Wafers
High-silicon wafers have a silicon content between 2.8% and 4.8%. While they possess excellent magnetic properties, they are relatively brittle. These silicon steel sheets are mainly used in the manufacture of transformer cores and are therefore also called transformer silicon steel sheets. In practical applications, high-silicon wafers are often used in the manufacture of large motors. Although their mechanical properties differ from low-silicon wafers, there is no clear boundary between the two in practical applications. Furthermore, high-silicon wafers can be further classified into hot-rolled and cold-rolled types based on their manufacturing process.
3. Differences in Silicon Content
Although both use cold-rolled silicon steel sheets, their silicon content differs. Specifically, the silicon content of cold-rolled non-oriented silicon steel sheets ranges from 0.5% to 3.0%, while that of cold-rolled oriented silicon steel sheets is higher than 3.0%. This key difference leads to significant differences in the magnetic properties and applicability of the two materials.
4. Differences in Manufacturing Processes
(1) The manufacturing process of non-oriented silicon steel sheets is relatively simple, involving hot-rolled or continuously cast steel billets to form coils approximately 2.3 mm thick. For low-silicon products, the coils are pickled and then directly cold-rolled to 0.5 mm thick; for high-silicon products, normalizing is performed first, followed by cold rolling to 0.55 mm or 0.37 mm thick, then annealing and a second cold rolling to 0.50 mm or 0.35 mm thick. This low-reduction cold rolling process helps promote grain growth during annealing, thereby reducing iron loss.
(2) Finally, both types of cold-rolled steel sheets are annealed in a continuous furnace at 850°C in a 20% hydrogen-nitrogen mixed atmosphere and coated with a phosphate and chromate insulating film. After being cold-rolled to the required thickness, the products are supplied as 0.35 mm and 0.5 mm thick steel strips. It is worth noting that the Bs value of cold-rolled non-oriented silicon steel is higher than that of oriented silicon steel.
Furthermore, the production process of grain-oriented silicon steel sheets requires stricter standards. It demands low oxide inclusion content in the steel and the addition of 0.03-0.05% carbon and inhibitors (second-phase dispersed particles or grain boundary segregation elements). These inhibitors control the growth of primary recrystallized grains and promote secondary recrystallization, thereby achieving a higher [001] orientation. However, the inhibitors themselves are detrimental to magnetism; therefore, high-temperature purification annealing is required after the inhibition process. During production, adding second-phase inhibitors requires increasing the billet heating temperature to ensure that the originally coarse second-phase particles can be dissolved and precipitated into fine particles during hot rolling or normalizing, thus enhancing the inhibition effect. Ultimately, the thickness of the cold-rolled finished product is 0.28, 0.30, or 0.35 mm. Cold-rolled grain-oriented silicon steel strip is produced by refining processes such as pickling, cold rolling, and annealing of 0.30 or 0.35 mm thick grain-oriented silicon steel strip. Compared to cold-rolled non-oriented silicon steel, grain-oriented silicon steel has significant advantages in reducing iron loss and exhibits strong directional magnetic properties. In the easily magnetized rolling direction, it exhibits excellent high permeability and low loss characteristics. Specifically, the iron loss of grain-oriented silicon steel strip in the rolling direction is only one-third that in the transverse direction, with a permeability ratio of 6:1. Meanwhile, its iron loss is approximately half that of hot-rolled steel strip, while its permeability is 2.5 times that of the latter.
5. Differences in Performance and Applications
Due to the differences in performance characteristics between grain-oriented and non-grain-oriented silicon steel, their specific applications also differ significantly. Cold-rolled non-grain-oriented silicon steel sheets play a crucial role in generator manufacturing due to their excellent performance and are therefore often referred to as cold-rolled motor silicon steel. Cold-rolled grain-oriented silicon steel strips, due to their unique characteristics, shine in transformer manufacturing and are therefore called cold-rolled transformer silicon steel.
