Corrosion behavior of plain carbon steels under different heat treatment conditions in freely aerated 3.5% NaCl solution

Abstract

The present work discusses the effect of the role of interlamellar spacing, % pearlite and pearlite colony size on corrosion behaviour of plain carbon steels (0.002%C, 0.17%C, 0.43%C, and 0.7%C) under different heat treatment conditions using the electrochemical tests in freely aerated 3.5% NaCl solution. Hence, ultra-low carbon (~100% ferrite), low and medium carbon (ferrite-pearlite steels having ~ 32.74% and ~ 52.34% pearlite, respectively) and high carbon steels (~100% pearlite) have been used in annealed conditions. In addition, four different variants (coarse, medium, fine, and very fine) of pearlite steels have also been developed by suitable heat treatment (annealing, as-received, normalizing and force normalizing, respectively) processes using the 0.7% carbon steels to understand the role of interlamellar spacing and pearlite colony size on corrosion mechanisms of pearlitic steels. The corrosion rate of the steel was increased as the carbon content increased. However, the corrosion susceptibility of high carbon pearlite steels was increased in the following sequence: air-cooled-forced air-cooled-as-received-furnace annealed steel since variations in the finesse of the pearlite microstructure significantly alter the corrosion behaviour of pearlite steels. The normalized steel has shown the lowest corrosion susceptibility as compared to the force normalized steel due to the entanglement of cementite causing short-circuiting of the galvanic couples. The FE-SEM was used to examine the corroded specimens after polarization tests and found that the corrosion performance of the steels has mainly been guided by the joint effect of fraction of pearlite, interlamellar spacing, and pearlite colony size.