Soft crystalline magnetic materials, - Non-oriented FeSi sheets

Non-oriented FeSi laminations (i.e., without a sharp texture and therefore without marked magnetic anisotropy) are soft magnetic materials (by far the largest category in terms of tonnage), crystalline and conductive, and inexpensive, which makes them ideal for low-frequency mass applications in electrical engineering, such as rotating or static electrical machines (small transformers), certain actuators, shielding, sensors and inductors.

After rolling and annealing, these traditionally metallurgically produced materials become polycrystals with varying degrees of texturing and silicon alloying, depending on application requirements. The aims of this article are to :

• summarize the main general characteristics of FeSi electrical steels, which are often useful in design offices;

• shed light on the typical behavior of these materials under temperature, frequency and stress loads;

• present the state of the art of the various current families of FeSi(Al) industrial laminations, in relation to their main use values and applications. A distinction will be made between the two major semi- and fully-processed sub-families, along with their advantages and disadvantages;

• present current or expected developments in FeSi laminations, covering both progress in production processes towards cleaner, less expensive materials that consume less energy to produce, and developments in applications (wind turbines, hybrid vehicles, turbogenerators, etc.) leading to the development of specific materials that are less dissipative and/or more mechanically resistant.

Although non-oriented FeSi laminations are widely used in most areas of electrical engineering, thanks to their low cost and excellent magnetic properties, they are unable to meet many more specific requirements, such as high power density, very low energy consumption, medium-to-high frequency performance, corrosion resistance and very high magnetic permeability. In such cases, it is necessary to resort to other, more expensive families of soft magnetic materials, such as FeNi, FeCo and FeCr alloys, magnetic amorphous materials, nanocrystalline ribbons or soft ferrites, etc., which are the subject of separate articles.