The effect of microstructure and non-metallic inclusions on corrosion behavior of low carbon steel in chloride containing solutions

• Oxide inclusions do not affect active dissolution but weaken passivation.
• Varying the steel microstructure has little effect on active steel dissolution.
• Passive currents and breakdown potentials are sensitive to steel microstructure.
• Increase of the sulfur content in steel results in weaker passivation.
• Voltammetric parameters can be used to predict corrosion behavior under open circuit.

The effect of microstructure and inclusions on corrosion of API-5L Х60-Х100 low carbon steel is examined in acetate buffer solutions (pH 6) containing chloride. Microstructure was varied by preliminary heat treatment resulting in following series: ferrite–pearlite, ferrite–bainite, ferrite–martensite, and demonstrated the minor effect on the active dissolution kinetics, as well as oxide and sulfide inclusions. The current in the passive region and breakdown potential appeared to be sensitive to both types of inclusions and steel microstructure. Voltammetric parameters are listed which correlate with corrosion rate under open circuit and can be used to predict both short- and long-term corrosion behavior.