According to the known art, magnetic steel sheets having a layer that improves the electrical insulation are used, for example, in electric drives for the design of stators. The materials used are regulated by the standard EN 10106 (1995). The materials named in this standard give a wide-ranging product range in order that the demands of different applications can be satisfied. The usable materials range from low-alloyed steel, with outstanding magnetic permeability, good thermal conductivity and good stamping properties, to higher-alloyed steels having very low remagnetization losses even at higher frequencies. As alloying constituents, the alloys in the standard contain copper (<=0.02%), manganese (<=1.2%), silicon (0.1-4.4%), aluminum (0.1-4.4%), the sum formed from the silicon content and twice the aluminum content being <5%, phosphorus (<=0.15%), tin (<=0.2%) and antimony (<=0.2%). Iron forms the basis of the alloy.
Coatings which improve the insulation between the individual steel sheet layers and the processability have been developed for improving the properties of the magnetic steel sheets. The specific properties of the material used have to take into consideration influencing variables, such as corrosion protection, electrical insulation, influence on the stamping properties, heat resistance or weldability. Coatings for magnetic steel sheets can be gathered from the standard EN 10342 (2005).
The magnetic steel sheets available in the aforementioned standards, and the coatings thereof, cannot withstand all fields of use, however, as has been shown. Particularly when the magnetic steel sheets are exposed to highly corrosive media, e.g. sour gas (high hydrogen sulfide content), these magnetic steel sheets are at great risk of corrosion.