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Abstract
Carbon strain-ageing has been studied in a vacuum-melted Fe–0·05% C alloy heat-treated to contain ∼6, 14, and 150 ppm carbon in solution. Damping and electron microscopy were used to follow the progress of ageing at 40° C (313 K) after 10% elongation. The decay of damping during strain-ageing was resolved into two components: Snoek damping and dislocation damping. The decay of Snoek damping obeyed the kinetics predicted by Meisel for segregation of carbon to atmospheres about dislocations. The decay in amplitude-independent dislocation damping followed the damping kinetics predicted by Granato et al. Hence, the decay rates of both types of damping support the theory that carbon atoms migrate to, and pin, dislocations during the initial stage of ageing. Furthermore, the Snoek damping results imply that migration of carbon to dislocations continues long after the dislocations are fully pinned. By transmission electron microscopy, small dark spots were detected in the matrix of highly supersaturated strain-aged specimens after ∼ 1400 min ageing at 40° C (313 K). No spots were detected in the specimens initially containing 6 and 14 ppm C, even after ageing for up to 1 year at 40° C (313 K). These spots were interpreted as arising from the coalescence, during ageing, of carbon-stabilized vacancy loops.