DYNAMIC RECRYSTALLIZATION - SCIENTIFIC CURIOSITY OR INDUSTRIAL TOOL

Rolling processes are categorized by the lengths of their interpass times: those that involve interpass intervals significantly longer than 1 s (e.g. reversing mills) are particularly suitable for conventional controlled rolling or recrystallization-controlled rolling; by contrast, those involving interpass times of 15-100 ms or more (e.g. the finishing trains of tandem mills) are shown to be suitable for dynamic or metadynamic recrystallization-controlled rolling. This distinction relies on the minimum time required to permit strain-induced precipitation, the occurrence of which inhibits both static and dynamic recrystallization. The effect of metadynamic recrystallization on the austenite grain size and on the retained strain is described. Examples are given of industrial processes in which dynamic recrystallization can play an important role. These include the stretch-reducing mill for the finishing of of seamless tubes, the finishing stages of rod rolling, and the finishing of microalloyed steels in hot-strip mills. The practical consequences of dynamic recrystallization on the microstructures produced by these operations and on the modelling of rolling load are also described.