*2.1. Materials*

The study was performed on two types of silicon steels labeled 200 and 300. The samples were supplied by Łukasiewicz Research Network according to IEC 60404 8 5 standard. Both samples in as-received conditions were covered with a phosphate protective coating. Each time prior to a test, the coating was removed by grinding the surface with SiC abrasive paper up to 1200 grit and finishing the surface with levigated alumina, cleaned ultrasonically in absolute ethanol and dried before immersion in the tested solution.

The coating-free sample surface was analyzed on a spark spectrometer to identify the chemical composition of samples (Table 1).


**Table 1.** Chemical composition of the tested samples.

#### *2.2. Metallographic Analysis*

The metallographic analysis was carried out by etching the samples with a nital solution (e.g., 4% HNO3 solution) and then degreased with absolute ethanol and dried. Grain size measurements were performed according to the ASTM E112 [19] method using a LEICA DM4000 M LED microscope (Leica Microsystems, Wetzlar, Germany).
