The Study Of Ending Colours Formed By Stainless Cloring Process

The coloring technology for stainless steel has been developed for more than40years, and the most widely used methods in industry are still INCO method. However, how to control the reproducibility of the color has been remained the major difficulty for this method. This study aims to investigate the influence of some factors mainly including pre-activation treatment and additives on the ending color of the stain steel. The specific works are as follows:The activation state of stainless steel surface was judged by the potential-time curve, and the activation degree and its influence regular on the coloring process was studied by polarization scanning and EIS (electrochemical impedance Spectroscopy) tests. It was found that potential-time curve can be used to judge the activation degree of the pre-activation treatment and when the potential reaches a stable value the surface obtains a roughly consistent activation state. The method for controlling of activation degree is beneficial for the subsequent controlling of the reproducibility of the color. The suitable activation degree judged by the way is important for obtaining excellent corrosion resistance of the color film.The influence of several additives on the ending color of stain steel was studied through a series of orthogonal experiments. It was found that the ending color was obviously influenced by MnSO4and boric acid and the coloring speed was obviously influenced by MnSO4and (NH4)6Mo7O244H2O4. While after adding four kinds of additives synchronously, MnSO4had the greatest influence on ending color and also on coloring rate, and the second influence was brought by boric acid.(NH4)6Mo7O244H2O4and ZnSO4showed no effect on coloring process.The influence rule of the proportion of main components in coloring solution was researched. And the composition of colored films with different color was studied by X-ray photoelectron spectroscopy (XPS). It was found that the ending color changing from green, purple, gold to black with the decreasing of CrO3concentration. In solution which simply contained CrO3and H2SO4, the concentration of CrO3directly affected coloring rate and played a major role in the forming of the ending color. The role of H2SO4was to promote the coloring reaction. The XPS analysis revealed that the composition of colored films is mainly in the form of oxides and hydroxides of Cr, Fe. The content conforms to the follow sequence: Cr3+(OX)>Cr3+(hyd)>Cr6+(OX), and Fe3+(hyd)>Fe3+(OX)>Fe2+(OX). The content of Cr element plays a more prominent effect on ending color than Fe element.