The strain-induced accelerated corrosion has been reported for many alloys used in structural and functional applications. To understand the effect of cold-work on corrosion behavior of alloys, specimens of carbon steel A569, strained to different amounts by cold-rolling, were used. The strain energy stored in cold-rolled specimens can increase the driving force for the iron oxidation reaction, therefore influencing the repassivation and corrosion behavior of A569. As a result, cold-rolled carbon steel specimens, in their active state, undergo a higher general corrosion rate than the equivalent annealed carbon steel specimens. In stable repassivation conditions, repassivation of the cold-rolled A569 specimens is slightly faster than the annealed specimens, where the repassivation reaction is expected to dominate over the Fe oxidation reaction. On the contrary, under unstable-passivity conditions, the passive current increases with the cold work. The higher passive current due to the presence of cold-work results in the earlier pit initiation in polarization tests. Results from electrochemical tests on specimens with different amounts of cold-work are discussed in this paper.
Carbon steels are used in a variety of structural and functional applications. They can be used in transportation, infrastructure, boiler pressure-system, and so on. In order to fulfill various engineering needs, many processes are required to engineer the materials into different dimensions and shapes. Therefore, a very significant amount of strain can be introduced into the materials.
Cold-rolling mainly introduces a large number of dislocations, constraining the materials in a compressive state. Therefore, the strain energy associated with these dislocations is stored in the material, and this also results into the residual stresses. Johnston investigated the effect of strain on corrosion rate of Cu in a sulfuric acid solution, and reported enhanced corrosion rates for strained samples . The higher dissolution rate of X-65 carbon steel at the crack tip, where strain was concentrated, was reported during stress corrosion cracking in a near-neutral chloride-containing solution . Yaguchi and Toshio argued that the enhanced dissolution rate at the crack-tip had a dependency on local plastic strain during stress corrosion cracking . Strain does not only enhance the active dissolution rate for alloys, it has also been reported to decrease the stability of passive film [4-5, 8-9]. In addition, a number of researchers have demonstrated the effect of strain on the polarization behavior and pitting corrosion in steels [6-7, 10]. The active dissolution, passivation and pitting corrosion have been reportedly subject to either the global or the localized strain. However, no single governing mechanism has been agreed upon that explains the interplay of strain and different forms of corrosion.