Fig. 1 EIS results of the steels subjected to preprocessing in solutions F1-F3: a-c Nyquist and Bode plots and corresponding equivalent circuit model for fitting the plots, d Rp values of the steels

Fig. 2 XPS wide-scan spectra a and narrow-scan spectra for b Si2p, c W4f and W5p, d Fe3/2p, e O1s of the steel subjected to pretreatment in solution F3 and f the corresponding atomic percent of elements as a function of sputtering depth

Fig. 3 Cross-sectional morphologies, relevant EDS analysis and corresponding average scale thicknesses of the preprocessed steels (F1-F3) following oxidation. F0 represents the oxidized bare reference devoid of preprocessing. The scale thickness of F0 was evaluated using a profilometer on the oxidized surface due to severe oxide spallation and associated difficulties in getting a cross section with detectable scale

Fig. 4 3D relief patterns and scratched morphologies of the oxidized steels without (F0) and without pretreatment (F1-F3)

Fig. 5 Snapshots of the structures following silicate and tungstate adsorption on the surface of Fe(110) and adsorption energy of the two structures within 1000 ps at 50 °C

Fig. 6 Phase diagram of the pretreated steel depicting oxygen partial pressure against W content at 950 °C. The Mn content in the system was set at 1.25 wt%, the Si content at 0.2 wt% and the W content was maximized at 10 wt%