Dynamic recrystallization kinetics model of X70 pipeline steel

In order to develop an integrated kinetic model of dynamic recrystallization (DRX), hot compression tests were performed in X70 pipeline steel over a temperature range of 1173–1473 K and strain rate range of 0.05–15 s−1 on a Gleeeble-3500 thermomechanical simulator. The stress–strain data was well smoothed and investigated. The onset of DRX was detected from the inflection point on the curve of strain hardening rate versus flow stress which can be well described by a third order equation. The activation energy of DRX and Zener–Hollomon (Z) parameter were determined by regression analysis of experimental stress–strain data. An approach based on the relationship between dislocation density and stress was used to quantify the fraction of DRX and in this case, a revised Avrami equation was developed. The good agreement between prediction value and experimental results proved the verification of the kinetics model of DRX.

► Strain hardening rate as a function of flow stress was well described by a third order equation.
► The onset of DRX was determined from the inflection point of the third order equation.
► Zener–Hollomon parameter was determined to be a criterion of DRX.
► DRV stress was estimated and the fraction of DRX was computed.
► A revised DRX kinetics model based on Avrami equation was developed.