Eco-friendly Stainless Steel Pretreatment Technology And Its Application Research

Although stainless steel has good corrosion resistance, it can produce corrosion in the bad environment,such as in chemical and halogen environments.One of the effective corrosion protection methods is to passivate the surface with hexavalent chromate, because of its good corrosion resistance and high damage tolerance. However, it inevitably causes a very serious air and water pollution and inhaled hexavalent chromium is recognized as a human carcinogen. It is urgent to develop an new environmentally friendly alternative to replace the chromate coating. In recent years, one of the non-toxic systems, organic acid with hydrogen peroxide (H2O2) as passivating agent, has attracted an extensive attention.In our work, three systems including citric acid, phytic acid and the rare earth-phytic acid have been used to passivate430stainless steel (43OSS) surface. The corrosion inhibition performances of these three passivation coatings were studied by potentiodynamic scanning and blue point test and the main results are shown as following:(1)The passivation layer with citric acid was obtained on430SS surface successfully. The optimized temperature and formula for processing are30℃and the ratio3:12:5of citric acid/hydrogen peroxide/ethylalcohol.(2)The passivation layer with phytic acid was obtained on430SS surface successfully. The optimized temperature and formula for processing are75℃and the ratio35g/L:5g/L:35g/L:5g/L:30ml/L of sodium silicate/sulfuric acid/hydrogen peroxide/nitric acid/phytic acid. The result of the electrochemical polarization measurement shows that the corrosion potential of the passivation layer can achieve0.050740V.(3)The passivation layer with rare earths-phytic acid was obtained on430SS surface well. The optimized temperature and formula for processing are50℃and the ratio7.5g/L:100ml/L:5ml/L:30ml/L of cerous nitrate/hydrogen peroxide/sulfuric acid/phytic acid.The morphologies characterized by atomic force microscopy (AFM) and Scanning Electron Microscope (SEM),The result of the electrochemical polarization measurement shows that the corrosion potential of the passivation layer can reach0.23578V.