The Effect Of Oxide Film On The Electrochemical Corrosion Behaviors Of Hot Rolled Steel

Steel has become the backbone material of the modern world because of its many unique and irreplaceable characteristics and properties and will remain the foundation for future industrial development and progress. But the oxide scale on the hot rolled steel will affect its corrosion resistance. The effect of oxide film on the electrochemicalcorrosion behaviors of hot rolled steel is not understood enough yet, so the subject has theoretical and practical values.The morphology and defects of oxide scales are characterized by scanning electronic microscopy (SEM) and charge coupled device (CCD).Effect of oxide scales on the behaviors of hot rolled steel were investigated by potentiodynamic polarization curves, electrochemical impedance spectroscope(EIS) and cyclic voltammetry(CV). The results indicated that there were many defects on the oxide scale of hot rolled steel. The oxide scales had only physical shielding effect on B510L , SAPH370 and A572GR55 hot rolled steel. It did not affect the corrosion reaction and the mechanism. Anodic and cathodic reaction of the hot rolled steel occurred through the defects of the oxide film. The oxide scale affected the corrosion rate mainly through the exposed area under the defects. The porosity of the oxide scale was proportional to the corrosion current under the oxide scale. The porosity could be reasonably assessed by the corrosion rate and the polarization resistance.To A572GR55 hot rolled steel, In the case of oxygen deficiency ,the oxide film took part in the cathodic reaction ,so the mechanism of cathodic reaction changed. The electrochemical impedance spectra of hot rolled steel and carbon steel showed single capacity. The hot rolled steel dipped in 3.5%NaCl solution in different time,it indicated that with the time along ,the oxide film was saturated by water or Cl-,so the physical shielding effect was lost.The protective oxide film should be intergrity, compactness, continuous and less crystal defects. Improving the hot rolling technology and the compactness and reducing the porosity of the oxide scale can make the oxide scale more protective.