| Preparation of colored stainless steel usually takes advantage of chemical colouring method, which is the mainly means to obtain colored film. The shape of materials can be very complicated and the coloring will be uniform by chemical colouring, which are merits of it. However, the colour recurring is difficult for chemical colouring. At present, all the study work on chemical colouring based on INCO method, and the component of colouring solutions are: CrO3 200~300g/L, H2SO4 250~500g/L, temperature 80~90℃. The oxide of Cr, Fe and Ni will be formed on stainless steel surface by colouring processes. The colour of film changed with thickness. The potential of stainless steel changed with time during colouring processes. There is correlative relation between the potential difference and colour of stainless steel. The correlative colored films can be obtained by controlling the correlative potential differences. The corrosion resistance of colored film is superior to stainless steel. Various colored film have different corrosion resistan.ce, which depends on the element distributes and configuration of film.Based on some important results and conclusion from previous work, major content of this paper is listed as follows:(1) Eperiment of chemical colouring of lCrl8Ni9Ti stainless steel with proper additives added to CrO3-H2SO4 colouring solution is studied. The colored film with the best corrosion resistance is obtained by colouring with the processes of CrO3 250g/L> H2SO4 270ml/L> proper additives 20g/L, colouring temperature 50℃, time 30min The results show that the addition of proper additives can improve the colouring speed and decrease colouring temperature 30~40℃.(2) The potential-time curve during colouring measured, and the effect of amount of additives and time on colouring processes of stainless steel are discussed. The potential differences of several colored film with different colour are confirmed according to the potential-time curves, and the correlative relation between the potential difference and colour of stainless steel is discussed. The correlative colored films can be obtained by controlling the correlative potential differences, which improved the colour recurring of chemical colouring processes successfully.(3) The electrochemistry stability of colored film is studied by potentiodynamic anodic plarization; The element distributes and configuration of yellow film and blue film are analysed by x-rayphotoelectron spectroscopy and glow discharge optical emission spectrometry, which discussed the difference of corrosion resistance of them.(4) The pitting origins of colored film are characterized by SEM and electron spectroscopy and the composition of pitting products are confirmed and measured by XRD. The primary study on pitting mechanism of colored stainless steel and the model of pitting growth are initiated in this paper. |
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