Effect of Tempering at 200 ℃ on Electrochemical Behavior of X80 Steel in NaHCO3 Solution

X80 pipeline steel was tempered for 30min at 200 ℃ with a heat treatment furnace, and then the electrochemical behavior of X80 steel before and after tempering in the solution of NaHCO3 was studied by the method of potentiodynamic polarization , electrochemical impedance spectroscopy and so on. The results showed that the corrosion was the type of cathodiz control. The corrosion potential of the X80 steel was reduced from -0.75 V before tempering to -0.80 V (SCE) after tempereing, and the passive current increased from 5.48 μA·cm-2 before tempering to 17.82 μA·cm-2 after tempered; AC impedance measurements show that the passive film of tempered X80 steel was loose, which is consistent with the observations of atomic force microscopy.