Abstract
Samples of Inconel 600 were thermally aged at 739 °C from 1 up to 300 h followed by water quenching. The changes in microstructure were characterized and its effect on sensitization was evaluated by subjecting the heat-treated samples to double-loop electrochemical potentiokinetic reactivation (DL-EPR) tests. The evolution of the microstructure was analysed in terms of grain size, carbide formation and chromium diffusion by optical and scanning electron microscopy. The results showed that the formation of chromium carbides is rapid at this temperature, increasing the density of carbides at the grain boundaries in the early stages of the ageing treatment. The formation of Cr7C3 and Cr23C6 along the grain boundaries and within the austenitic matrix modified the corrosion behaviour as seen in the measurements of the degree of sensitization (DOS). A decrement in DOS was seen with ageing time up to 200 h, due to the redistribution of chromium, induced by the equilibrium between chromium at grain boundaries and within the matrix. Electron backscattering diffraction suggested that self-healing of the alloy may be due to the mechanism of near-boundary gradient zones, where the increased number of dislocations leads to precipitation of carbides by promoting diffusion and thereby decreasing the Cr-depleted zones.
Published Version
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