Abstract
Serrated flow in the austenitic state of 300 grade commercial marageing steel has been investigated in the strain rate range from 4.17 × 10−5 to 1.67 × 10−2 S−1 and at temperatures between 325 and 700°C. The strain exponent (m + β) was found to be 1.5, which is in agreement with Saada's model of vacancy generation and which also suggests that the mobile dislocation density remains constant during plastic deformation at various strain rates. The solute responsible for the onset of serrations was found to be Mo atoms from the activation energy for solute migration and from the identification of precipitates by transmission electron microscopy. In the serrated flow region higher work-hardening, lower ductility, and negative strain rate sensitivity were also observed. At higher temperatures, where serrations were absent, a very large amount of total elongation was observed which may be attributed to superplasticity.
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