Origin of Interference Colors on Austenitic Stainless Steel

Data are presented on the coloring conditions, colored layer parameters, and color characteristics of stainless steel 304 samples treated in an electrolytic cell (60 Hz, 100 mV) using a mixture of 5 M sulfuric acid and 2.5 M chromic acid. Reflectance spectra indicate that the samples have high-purity color mainly in the yellow region and that the color is due to interference oscillations in the visible range. In addition, reflectance data in conjunction with composition-depth profiles obtained using glow discharge spectrometry indicate that the coloration of the samples is due not only to reflectance oscillations but also to the subtraction effect. The reduced Fe content and significant oxygen content in the near-surface region attest to the formation of a mixed oxide layer. Atomic-force microscopy examination indicates that the sample surface has an island structure.