What is the maximum reduction possible through cold=working in zirconium alloy tubes? And what is the annealing temperature to restore the mechanical properties?
There are several zirconium alloys for nuclear applications. Their structure, properties and heat treatment depend on the chemical composition, exact applications of parts and operation condition for fuel assemblies
The ductility of zirconium materials increases significantly with an increase in rolling temperature at the range between 300 and 500ºC. In static recrystallization studies, this shows that the zircomium materials with similar recrystallized grain size cold-rolled with a thickness reduction of 55%. The cold rolled strips if annealed for one hour between 4500 - 600ºC indicates the increase in ductility by three main causes: enhanced number of slip systems, the occurrence of cross slip and increase in the mobility of dislocations.
During annealing after cold-rolling with a thickness reduction of 55%, Zr alloy softens by recovery and recrystallization, but the relative contribution of recovery is less pronounced for the alloy. The interaction of solute atoms with dislocations explains the smaller contribution of the recovery processes to the softening of the alloy. The interaction of solute atoms and precipitates with migrating grain boundaries explains the need of greater thermal activation for the occurrence of recrystallization in the alloy. After recrystallization, the crystallographic orientation of the basal planes changes , however, pure zr remains stable.