Influence of cementite coarsening on the corrosion resistance of high strength low alloy steel

Abstract A detailed study was carried out on how heat treatment affects the initiation and evolution of localized corrosion on E690 steel in a simulated marine environment. Localized corrosion was mainly induced by the inclusions and initiated by dissolution of the distorted matrix surrounding the inclusions. In this early corrosion initiation stage, localized corrosion induced by inclusions is the main form of corrosion. The chemical and electrochemical processes of matrix deformation and localized corrosion induced by inclusions are explained in detail. With the immersion time increased, galvanic contributions at the ferrite-austenite interfaces and the coarsened carbides reduced the polarization resistance in the annealed specimen and therefore accelerated corrosion compared to the as-received specimen. Hence, the heat-treated specimen showed a lower charge transfer resistance than the one without heat treatment. This promoted a shift from localized to uniform corrosion. Lastly, a corrosion initiation and evolution model has been established to explain the corrosion process of E690 steel in the marine environment.