Corrosion resistant coloured chromium oxide coatings on stainless steel

Corrosion resistance and artistic appearance of passive chromium oxide coatings developed over stainless steel by chemical conversion methods are revisited. Preparation technique and thermal processing of the films were optimized to improve protection efficiency and the control of colour development - from yellow to green through violet - is at present under study. Film structure and composition were studied by X-ray diffraction and soft X-ray absorption spectroscopy (XAS) using synchrotron radiation to assess element speciation. Surface microstructure was monitored by SEM observation. Enhanced passivation behaviour of thermally processed films is related to the formation of a spinel-type phase after migration of manganese from the bulk steel to oxide coating surface.