The synergy between cementite spheroidization and Cu alloying on the corrosion resistance of ferrite-pearlite steel in acidic chloride solution

In this work, the corrosion behavior of medium-carbon steels (45, 45Cu and 45Cuq steels) in acidic chloride environment was investigated. The results indicated that the micro-galvanic effect between the anodic ferrite matrix phase and the cathodic cementite secondary phase notably affected the corrosion resistance of the three steels. For 45 steel, serious pitting corrosion happened in and around the pearlite regions, and a large number of lamellar cementite was fixed in the corrosion pits. Meanwhile, the continuously increasing superficial area of cathodic cementite enhanced the micro-galvanic corrosion, resulting in a rapidly increase in corrosion rate with time. While for 45Cu and 45Cuq steels, macroscopic uniform corrosion occurred, and the cementite accumulation was markedly reduced as compared with 45 steel, thus the micro-galvanic effect was weakened and the corrosion rate was decreased accordingly. Among these, 45Cuq steel showed the most stable and excellent corrosion resistance during long-term corrosion, indicating the occurrence of a synergistic effect between cementite spheroidization and Cu alloying, thereby significantly improving the corrosion resistance of 45 steel.