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DRX

DRX: Dynamic Recrystallization
Definition:Dynamic recrystallization
Explanation:DRX is a softening mechanism which involves nucleation and growth of new grains within a deformed microstructure at elevated processing temperatures. On the contrary to static recrystallization (SRX) which occurs after deformation, DRX occurs during the deformation process.

An important parameter in DRX is the critical point for its onset: when the stored energy reaches the maximum in the material, a further storage of dislocations is not possible and DRX starts. Determination of the onset is not straightforward, since it is not indicated by a distinct point in the flow curve. Poliak & Jonas [1] proposed that when plotting the strain hardening rate with respect to the stress, an inflection point on the curve indicates the critical stress point where DRX starts.

In addition to the onset, the DRX kinetics is also important for the final mechanical properties and microstructure. For this purpose, it is common to introduce an Avrami type equation for the recrystallized fraction and relate its influence on the flow behavior in the form of a mixture law.
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Diagram:

Stages of microstructure evolution during hot rolling. An initial microstructure undergoes DRX and forms a fine grain structure which later coarsens due to grain growth.
SFB-Link:Even though it is based on thermodynamics, the criterion of Poliak and Jonas can only be applied when the Avrami exponent is >3, which is not the case of high manganese steels. Therefore, a new thermodynamically consistent model for flow behavior in DRX domain was developed in the framework of SFB 761.
References:[1] E.I. Poliak and J.J. Jonas, "A one-parameter approach to determining the critical conditions for the initiation of dynamic recrystallization", Acta Metall., pp. 127-136, 1996.
[2] M. Bambach, “Implications from the Poliak–Jonas criterion for the construction of flow stress models incorporating DRX“, Acta Mater., pp. 6222-6233, (61) 2013.