Field of the Invention
The present invention relates to an iron-cobalt alloy. The invention alloy is particularly useful for the manufacture of magnetic circuits in electrical-engineering machines. A process for manufacturing articles, strips, etc. using the invention alloy also makes up part of the invention as does a sheet comprising the invention alloy coated with an electrically insulating layer.
Discussion of the Art
Electrical-engineering machines, such as electric motors, transformers or relays, include magnetic circuits consisting of stacks of pieces cut out from strips made of alloy whose magnetic properties are adapted. The greater the specific energy of the machines the better must be these properties, this being the case, for example, for machines on board vehicles such as airplanes or high-speed trains. This is because for these applications it is necessary to reduce to a minimum the weight of the equipment by increasing the specific energy, that is to say the power per unit of mass.
The magnetic circuits of machines having a high specific energy are often manufactured from an iron-cobalt alloy whose chemical composition comprises, by weight, approximately 50% of cobalt and 2% of vanadium, the balance being iron and impurities. However, these alloys have several drawbacks because they all exhibit an .alpha.-.gamma. phase transformation which very appreciably limits the scope of varying the magnetic properties by heat treatment. In addition, these alloys generally have too low an electrical resistivity and are too expensive.
It has been proposed, especially in DE-C-705 516, to use iron-cobalt-silicon alloys containing from 2% to 18% of cobalt and from 1% to 6% of silicon. However, these alloys do not provide a satisfactory solution to the problem mentioned hereinabove. This is because, in order to obtain satisfactory magnetic properties, it is necessary that the alloy contain more than 3% of silicon. It then becomes very brittle and can no longer be cold-rolled satisfactorily, it therefore no longer being possible to obtain the low thicknesses which are desirable in order to reduce the eddy-current losses in the magnetic circuits.