Abstract
The acoustic emission (AE) during deformation of a Fe–3·5Ni–0·2C alloy has been measured after isochronal tempering for 100 min at temperatures in the range 50–650°C. The emission was greatest in specimens tempered in the range 200–300°C. The origin of the isochronal tempering peak appears to be the rapid propagation (∼2 × 103 m s−1) of groups (n ≳ 5) of dislocations over distances comparable to the lath packet size. This process is inhibited by the presence of strong precipitates in the lath interior and a high forest dislocation density. Strong precipitates were present in both the quenched and high-temperature (> 400°C) tempered states. Within a critical tempering region the precipitates produced during quenching had in the main disappeared, while the large spheroidal precipitates seen in the high-temperature tempered samples were still very small. It is possible that these precipitates could be sheared by dislocations, thus providing conditions for the generation of detectable AE signals.
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