The strain-rate sensitivity of the plastic properties of α-iron at high temperatures

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Abstract
The tensile stress-strain behaviour of high purity iron has been examined over a range of temperatures from 0° to 900°C and strain rates from 0·04 min−1 to 40 min−1. The changes in flow stress which occur during instantaneous changes in strain rate have been measured and calculations of the activation volume for the thermally activated part of the flow stress have been made. The activation volume is found to be independent of strain for a given set of testing conditions and equal to the activation volume calculated from the strain-rate variation of the yield stress. The activation volume ranges from 10−21 cm3 to 9 × 10−21 cm3, increasing with increasing temperature and decreasing strain rate but it is not a unique function of the effective stress in the deforming material. The results can be best explained if the thermally activated part of the flow stress is controlled by the non-conservative motion of jogs in screw dislocations.