Abstract
A colored film was formed on SUS 430 and SUS 304 stainless steels in 5kmol m-3 H2SO4 at 353K by the potential-pulse method and some porous surface structures were observed under SEM observation. When anodic pulse potential was controlled at the transpassive potential, the film obtained showed good adhesion, but film obtained at high potentials dissolved along to the grain boundary. Active dissolution occurred when the cathodic pulse potential decreased to the active dissolution potential region. The films grown were thicker than those obtained by the sulfuricchromic immersing method or the alkaline electrolysis method. The thickness of surface films on SUS 430 and SUS 304 increased lineally with electrolytic time. Within the coloring time range, the growth rate tended to increase with increases in the anodic pulse time or decreases in the cathodic pulse time. It was found by XPS analysis that in films on SUS 304, Cr was enrichened and Fe and Ni were depleted, and that the films consisted of a complex compound of Cr and -OH at the surface layer of the film, and an oxide consisted of Cr with a little Ni and Fe at the inner layer. X-ray diffraction showed the surface film had an amorphous structure. It was also found that resistance to pitting corrosion was improved by increasing the electrolysis time.
