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TALLIZATION during the interpass times and after hot deformation plays a major role in microstructure evolution during hot rolling. Three different mechanisms are believed to be responsible for restoration after deformation, or during intervals between deformations. These are static recovery (SRV), static recrystallization (SRX), and postdynamic recrystallization (post-DRX).* Also, after complete *This is often termed metadynamic recrystallization (MDRX), a term that here will be taken to represent recrystallization by the static growth of nuclei formed during DRX.

recrystallization, grain coarsening will take place in the recrystallized structure. However, in austenite, recovery plays a significant role only in slightly deformed structures or during the early stages (i.e., short times of annealing) of restoration for heavily deformed microstructures. In the latter case, between 10 and 20 pct of the softening of the microstructure is by recovery. The recrystallization following deformation is usually termed SRX or post-DRX, for the nucleation and growth of new grains or the growth of DRX nuclei, respectively. A combination of any two or more of these mechanisms is possible under different conditions.

A. DEHGHAN-MANSHADI, Research Fellow, formerly with the Centre for Materials and Fibre Innovation, Deakin University, Geelong, VIC, 3217, Australia, is with the Faculty of Engineering, University of Wollongong, Wollongong, NSW, 2522, Australia. Contact e-mail: [email protected] M.R. BARNETT, Associate Professor and P.D. HODGSON, Professor, are with Centre for Materials and Fibre Innovation, Deakin University, Geelong, VIC, 3217, Australia. Manuscript submitted November 29, 2007. Article published online April 15, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A

The hot deformation conditions (i.e., strain, strain rate, and temperature) have different effects on each recrystallization process. Strain has been shown to have little effect on the rate of post-DRX,[1–3] such that the kinetics of post-DRX are considered to be strain independent. In contrast, the SRX kinetics are often expressed as a power-law function of strain.[1–6] The strain to the peak stress (ep) has usually been used to separate between SRX and post-DRX. Once the applied strain is larger than the peak strain, post-DRX takes place during the softening and it does not vary by strain. It has been proposed[2] that all the nuclei are presented at the end of deformation to the peak strain, and further deformation does not lead to any additional nuclei. Therefore, at strains beyond the peak, softening is strain independent. At strains lower than the peak, a complex combination of static and post-DRX occurs, and the softening is a power-law function of strain. It has been shown that post-DRX is largely dependent on strain rate[2,7–10] and weakly dependent on temperature[2,7] and composition, whereas SRX is a strong function of both temperature and grain size and depends only weakly on strain rate.[1,11,12] However, the strain rate did not appear to affect the general