Review of Fe-6.5 wt%Si high silicon steel-A promising soft magnetic material for sub-kHz application

To meet the growing need for energy efficiency in power electronics and electric machines, a number of new soft magnetic materials are being investigated. Among them, high silicon Fe-Si alloy has been recognized as a promising candidate for low-to-medium-frequency applications. Compared to the currently most widely used 3 wt% silicon steel, the steel containing 6.5 wt% Si possesses more favorable properties, including high electrical resistivity, good saturation magnetization, and near-zero magnetostriction. However, the high silicon content facilitates the formation of ordered phases, resulting in severe brittleness that prohibits mass production using the economical conventional processing methods. A number of new processing routes have been investigated and inspiring progress has been made. Prototypes of motors and transformers using high silicon steel have been demonstrated with improved efficiency and power density. If the processing cost and limitations of size and shape are properly addressed, high silicon steel is expected to be widely adopted by the industries. Among all the investigated processing techniques, rapid solidification appears to be the most cost-effective method for mass producing thin sheet of high silicon steel. This paper reviews the current state-of-the-art of the Fe-Si based soft magnetic materials including their history, structure, properties, processing, and applications.