Soft magnetic materials are used for applications, such as core materials in inductors, stators and rotors for electrical machines, actuators, sensors and transformer cores. Traditionally, soft magnetic cores, such as rotors and stators in electric machines, are made of stacked steel laminates.
However, in the last few years there has been a keen interest in so called Soft Magnetic Composite (SMC) materials. The SMC materials are based on soft magnetic particles, usually iron based, with an electrically insulating coating on each particle. By compacting the insulated particles, optionally together with lubricants and/or binders, using the traditionally powder metallurgy process, the SMC parts are obtained. By using the powder metallurgical technique it is possible to produce materials having a higher degree of freedom in the design of the SMC part compared to using steel laminates, as the SMC material can carry a three dimensional magnetic flux and as three dimensional shapes can be obtained with the compaction process.
As a consequence of the increased interest in the SMC materials, improvements of the soft magnetic characteristics of the SMC materials is the subject of intense studies in order to expand the utilisation of these materials. In order to achieve such improvement, new powders and processes are continuously being developed.
In addition to the soft magnetic properties, good mechanical properties are essential. In this respect steam treatment of the compacted composite body has shown promising results as disclosed in the U.S. Pat. No. 6,485,579. According to the present invention it has been found that steam treatment can give unexpectedly good results, not only as regards the mechanical properties, but also as regards the soft magnetic properties provided that certain conditions as regards the type of powders, lubricants, and process parameters are fulfilled. In brief and in contrast to the invention disclosed in the US patent it has been found that the lubricant used in the iron or iron-based composition to be compacted should be of organic nature and that it should vaporize without leaving any residues in the compacted body before the steam treatment.