**Author details**

steady state flow as a plateau due to DRX softening is more recognizable at higher temper‐ atures and lower strain rates) with a varying softening rate which typically indicates the onset of DRX, and the stress evolution with strain exhibits three distinct stages; (3) at lower strain rates and higher temperatures, the higher DRX softening rate slows down the rate of work-hardening, and both the peak stress and the onset of steady state flow are therefore

Three characteristic points (the critical strain for DRX initiation ( *A*=2.44154×1025 ), the strain for peak stress ( *m*=3.85582 ), and the strain for maximum softening rate ( *ε*c )) which indicate whether the evolution of DRX can be characterized by the process variables need to be identified from the conventional strain hardening rate curves. A modified Avrami equation, *ε*<sup>p</sup> , has been introduced into this work to describe the kinetics of DRX, and then an integrated calculation process has been presented as an example of as-extruded 42CrMo high-strength steel. By the regression analysis for conventional hyperbolic sine equation, the dependence of flow stress on temperature and strain rate was described, and what's more, the activation energy of DRX ( *ε* \* ) and a dimensionless parameter controlling the stored energy ( *X*DRX =1−exp{ − (*ε* −*ε*c) / *ε* \* *<sup>m</sup>*} ) were determined. In further, the strain for maximum softening rate, *Q* , and the critical strain, *Z* / *A* were described by the functions of *ε* \* . Thus, the evolution of DRX volume fraction was characterized by the modified Avrami type equation including the above parameters. Based on the calculation results of this model, the effect of deformation temperature, strain and strain rate on the recrystallized volume fraction is as follows: as the strain increases, the DRX volume fraction increases and reaches a constant value of 1 meaning the completion of DRX process; for a specific strain rate, the deformation strain required for the same amount of DRX volume fraction increases with decreasing deformation temperature, which means that DRX is delayed to a longer time; for a fixed temperature, the deformation strain required for the same amount of DRX volume fraction increases with

increasing strain rate, which also means that DRX is delayed to a longer time.

The microstructures on the section planes of specimens deformed under different strain rates and temperatures were examined and analyzed under the optical microscope. The evolu‐ tion of grain boundaries and grain size were presented as an example of as-extruded 42CrMo high-strength steel. It can be summarized that under a fix temperature, as deformation strain rate increases, the microstructure of the as-received billet becomes more and more refined due to increasing migration energy stored in grain boundaries and decreasing grain growth

This work was supported by National Key Technologies R & D Program of China (ZDZX-DFJGJ-08), Science and Technology Committee of Chongqing (cstc2009aa3012-1), Fundamen‐

tal Research Funds for the Central Universities (Project No. CDJZR11130009).

shifted to lower strain levels.

86 Recent Developments in the Study of Recrystallization

time.

**Acknowledgements**

#### Quan Guo-Zheng

Department of Material Processing & Control Engineering, School of Material Science and Engineering, Chongqing University, P.R., China
