Potentiodynamic polarization studies of the pitting corrosion resistance and passivation behavior of P4 low carbon mold steel in chloride and acid chloride solution

Abstract

Potentiodynamic polarization studies and open circuit potential measurement of P4 low carbon mold steel (P4LC) was performed to assess its pitting corrosion resistance in specific concentrations of chloride and acid chloride solutions. Results showed the corrosion rates of P4LC were generally higher in the acid chloride media. P4LC displayed significant pitting resistance, independent of chloride concentration in the chloride media. The chloride attack was determined to be the consequence of film breaking and penetration mechanism. Delayed passivation coupled with metastable pitting activity occurred at the anodic region of the polarization plot in the acid chloride solution and beyond a certain chloride concentration in the acid chloride solution, passivation behavior of the steel was completely absent due to the combined electrochemical action of and Cl− ions. O2 reduction was the dominant cathodic in the chloride solution while H2 evolution was the dominant reaction in the acid chloride media. Data from open circuit potential analysis shows the oxide film formed on P4LC in the chloride solution was sustainable from the positive shift in corrosion potential while in the acid chloride solution the corrosion potential were more electronegative. The morphology of P4LC showed the presence of deep elliptical corrosion pits at low chloride concentration while at higher chloride concentration fewer but larger pits in the form of vertical grain attack were visible. The morphology of P4LC from the acid chloride solution showed the presence of large number of deep elliptical corrosion pits coupled with a more deteriorated surface.