What is a silicon steel - Knowledge

Silicon steels are ferritic alloys of iron and silicon that have magnetic properties which make them useful in motors and transformers. The silicon additions improve magnetic softness and increase the electrical resistivity. They also have the undesirable effects of decreasing the Curie temperature, reducing the saturation magnetization, and of embrittling the alloy when the silicon additions exceed about 2 wt.%. The embrittling effects of silicon make it difficult to produce silicon steels with more than about 3 wt.% silicon. The silicon steels are produced in two forms, highly textured grain-oriented alloys and alloys in which the grains are not oriented. Grain orientation is carried out to align the magnetic easy axis.

1.Silicon steels

Drastically better electrical performance as well as improved mechanical and magnetic properties were achieved by the invention of silicon steel in 1900. Depending on the exact amount of Si in the composition, either nonoriented, isotropic alloys or grain-oriented, anisotropic alloys, which are typically rolled into thin sheets, can be produced. Today, these two types of materials account for roughly 40% and 25%, respectively, of the global market for soft magnetic materials (Coey, 2009).

2.Iron-silicon alloys

Iron-silicon alloys containing up to about 4% Si used for magnetic applications are known as silicon steels. Higher-loss non-oriented silicon steels are generally used in small motors and generators, relays, and small power transformers where efficiency is of less concern, while the low-loss oriented grades tend to be used in large generators and power- and distribution-transformers where weight and efficiency considerations are of paramount importance.

As a result of intense research and development efforts over the years, the quality of silicon steels has been improved continually. Intense studies on the mechanisms of recrystallization textures and of magnetic core loss have led to the development of new grades of high-induction low-loss material of exceptionally sharp {110}〈001〉 texture.

3.Silicon–Iron Electrical Steels

The most common soft magnetic material used in electrical machines is silicon–iron electrical steel (see Steels, Silicon Iron-based: Magnetic Properties) in the form of thin laminations. The addition of silicon to soft iron results in a significant decrease in coercivity, a slight decrease in saturation magnetization, and an increase in resistivity. There are two distinct categories of electrical steels: nonoriented isotropic products with silicon contents in the range 1–3.5%, and grain-oriented anisotropic products which contain 2.9–3.15% Si (+Al). Silicon levels above 3.5% result in the steel becoming very brittle and hard to work. Oriented steels have the lowest core loss (see Table 1) and are used in transformers, whereas nonoriented steel is used in electrical machines as there are varying flux directions.

4.Steels: Classifications

Steels developed primarily for particular electrical, magnetic, and physical properties include the silicon steels (see Silicon Steels), magnetic steels (see Magnetic Steels) and steels having low coefficients of thermal expansion (see Steels: Low Expansion).