Fig. 8. Relationship between molar fraction of phases and temperature by multiphase-field model in Fe-25.3%Cr-16.4%Ni-2.5%Mo-0.24%N alloy.

An anodic dissolution behavior of oxide films formed on the SUS 430 and 304 stainless steels during annealing process was studied in acidic Na2SO4 solution using electrochemical techniques.Structural analyses of the films at various stages of the electrolysis process were also carried out by X-ray diffraction, Grow Discharge Spectroscopy (GDS) and ESCA techniques. Dissolution rate of the oxide was accelerated with anodic polarization, although it was not affected by the solution pH. It was found that major compounds of the oxide films of SUS 430 and SUS 304 stainless steels were (Fe, Cr) 2O3 and SiO2, and (Fe, Cr)203, FeCr2O4 and SiO2, respectively. By electrolyzing in the transpassive region Cr was dissolved whereas Fe and Si oxides remained on the surface of the stainless steels.