Abstract
The strain-ageing kinetics of annealed (870°C/1143 K) and quenched (700°C/973 K) single crystals and quenched (700°C/973 K) polycrystalline specimens of Ferrovac-E iron were studied over the temperature range −10°C (263 K) to 70°C (343 K) employing the yield-point return technique. Snoek rearrangement of interstitials about dislocations was deduced from the results as the first stage of the strain-ageing process. The completion time required for Snoek rearrangement corresponds to the time required for a single jump of an interstitial carbon or nitrogen atom. The ageing process obeys a t 2/3 relationship. Only minute amounts of interstitials are required: no drastic difference could therefore be observed between quenched and annealed specimens. The activation energy is in the range 14·1±2·3 to 14·9±0·5 kcal/mol (59·0±9·6 to 62·4± 2·1 kJ/mol). The first value is based on Arrhenius’ equation, the second on Hartley's analysis using 45 separate experimental determinations. The second state of strain-ageing is due to conventional long-range interstitial diffusion.
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