Magnetic non-destructive evaluation of the silicon distribution in a Si-gradient silicon steel lamination

Electrical steel, characterised by high permeability and low core loss, is essential for producing electrical converters. While adding silicon enhances its magnetic properties, higher silicon content reduces ductility, complicating traditional manufacturing processes. To address this, chemical vapour deposition (CVD) has been introduced to increase silicon content without mechanical contact. The local evaluation of CVD-treated steel is critical to prevent process-related issues and unexpected magnetic behaviours. Low-frequency magnetic incremental permeability (LF-MIP) has emerged as a promising non-destructive, localised surface method for this purpose. Although the correlation between magnetic indicators and silicon content is well-established under standard conditions, real-time, localised evaluation remains largely unexplored. In this work, we combine LF-MIP measurements with simulation results to propose an innovative method for assessing the complete silicon diffusion profile. Experimental results and simulations were integrated into a reference chart for post-processing, enabling precise predictions of silicon profiles in blind tests. With a relative Euclidean distance of less than 2% between our method’s predictions and destructive tests on CVD-treated 10JNHF600 specimens, the method is considered validated.