While silicon-iron was not primarily developped for shielding purposes, it offers some magnetic shielding properties that are used in certain applications where AC fields need to be shielded. The advantage of silicon iron lies therin, that the saturation in DC fields is rather high, offering good shielding properties to shield stray fields of strong magnets, such as those from NMR's.
However, it is in no way suitable to shield slow varying DC shifts such as often found in electron microscopy rooms, emanated from tram ways. It has been extensively tried by many people to use the rather inexpensive silicon iron to block those fields, however with no success. The magnetic properties simply do not allow to shield those fields.
Since the permeability of silicon-iron is rather low compared to mu-metal, the shielding attenuation is somewhat limited. However, in certain applications, like reducing magnetic AC fields of electrical equipment such as transformers, it might serve well.
Since silicon-iron consists of around 97% pure iron. A thin coating applied to the sheets provides a certain degree of corrosion resistance, however, without coating, it offers no corrosion resistance at all and will rust like a nail in wet or humid environment. On the other hand, it is cheap to buy, easy to handle and thus suitable for certain applications. Alternatively, pure iron might be used if thicker shielding is necessary, whereas silicon-iron would become to bulky when many layers need to be applied.
Silicon-iron, electrical steel, as per Wikipedia:
Electrical steel (lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is a special steel tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle, low core loss, and high permeability.
Electrical steel is usually manufactured in cold-rolled strips less than 2 mm thick. These strips are cut to shape to make laminations which are stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors. Laminations may be cut to their finished shape by a punch and die or, in smaller quantities, may be cut by a laser, or by wire EDM. Continue reading in Wikipedia .....