Studies On Corrosion Resistance And Anode Behavior Of Tin Free Steel

The use of tin free steel (TFS) products in a variety of packaging applications, particularly in crown cap, twist off cap, bottom cover the top of three-piece cans and drawn can, has increased steadily in recent years as TFS products exhibit an attractive combination of low-cost, good adhesion, good high-temperature resistance, strong anti-sulfur compared with tinplate products. However, point rust is generated easily on TFS surface in the process of product transportation, leading to decreasing application value of TFS. In addition, the plating solution has a characteristic of corrotion to anodic materials. This has influnced on the plating process. So corrosion resistance and anode behavior of tin free steel is researched significantly in this paper.Effect of CrO3concentration, NH4F concentration, temperature and the current density on corrosion resistance is carried out by using leaded alloy and mild steel plate as anode and cathode, respectively, by means of electrochemical polarization method. Based on the experiment of single element, the optimize process is found according to four elements and three levels of the experiment parameter, which is CrO3concentration140g/L, NH4F concentration3g/L, temperature40℃and current density40A/cm2.The impurity of Fe3+ions、Cl-ions、Na+ions、the particls from the anode into the standard plating liquid and the properties of anodic materils have an obviously effect on corrosion resistance of the TFS. The results show that the corrosion resistance of TFS is decreased with increase of the impurities concentration and the using time of anode materials.The electrochemical actions are studied anodic materials in Cr and F ions solution by using the method of CV and EIS. Electrolytes solution is Cr ions solution, fluorine ions solution and the mixed solution of Cr ions and F ions. The three kinds of CrO3concentration is130g/L,150g/L,170g/L. The three kinds of F ions solution concentration is3g/L,5g/L,7g/L. The concentration of the mixed solution of Cr and F ions is CrO3concentration150g/L, and the variation of F ions concentration3g/L,5g/L,7g/L. Electrochemical properties of graphite anode, lead oxide anode and lead alloy anode in above electrolytes solution are researched. The results show that the polymerization structures of Cr ions, F ions and the mixed Cr-F ions on anode surface have a remarkable effect on electrochemistry properties of anode materials. Inductive reactance phenomenon is observed on EIS for graphite anode and lead alloy anode in Cr ions solution. Compared with that of graphite anode and lead alloy anode, polarization resistance value of lead oxide anode is bigger. F ions may decrease the polarization resistance value of lead oxide anode in Cr ions solution， but increase that of graphite anode. As to F ions solution, polarization resistance value for the lead alloy anode is higher compared to that of graphite anode and lead oxide anode. The properties of F ions solution are found to eliminate the inductive reactance phenomenon, and increase the conducting ability of Cr ions solution. F ions have a characteristic of special chemical and corrosive properties, which presented the properties of not only inhibiting the chemical state transition of Cr ions, but decreasing the oxide current density of lead alloy and lead oxide anode.