Abstract: The corrosion behaviors of 20Cr9Ni5Co14 ultra high strength steel were studied by using electrochemical polarization (Potentiodynamic polarization, linear polarization and cyclic polarization technologies) and electrochemical impedance spectrum methods in different conditions corrosion, and the corrosion morphologies were characterized by using scanning electron microscopy (SEM). The results showed that the passivation phenomenon of 20Cr9Ni5Co14 steel disappears with the NaCl concentration increased while it appears in 3.5% NaCl solution. The corrosion current reduces from 8.223 × 10-7 A/cm2 to 1.129 × 10-7 A/cm2 with increasing NaCl concentration. The passivation potential and over passivation potential of 20Cr9Ni5Co14 steel increase with the increase of hydrogen ion concentrations. When the pH is higher than 3, the corrosion product film having excellent corrosion resistance which leads to the electrochemical polarization step as limited step, while the pH value reached 2, the corrosion products dissolute and the polarization caused by concentration differences becomes limited step. Corrosion morphology studies showed that the corrosion of 20Cr9Ni5Co14 steel in the polarization process oriented from pitting corrosion, which leads to reduction of corrosion resistance.

Key words: Electrochemical polarization, Electrochemical impedance spectroscopy, 20Cr9Ni5Co14, stainless steel