抄録
The dynamic recrystallization phenomenon during hot torsion of OFHC copper was investigated from various view points such as the flow stress behaviour, the grain refinement effect and the mechanism of recrystallization. The general characteristics of the stress-strain curves were to exhibit a marked peak, after which the flow stress decreased to a steady state value. A feature of the curves at low strain rates was the regular oscillation of flow stress during the initial stages of deformation. This is a deformation behaviour characteristic of dynamic recrystallization type materials.
There was a knee point on the plot of the relationship between the steady state flow stress and the Zener-Hollomon parameter (Z) at the condition of Z\simeq1012 sec−1, and from the results of microstructural observations at each deformation condition (Z value), it was understood that the equiaxed grain structure due to dynamic recrystallization was obtained in the Z value lower than this knee point. In this condition of Z lower than 1012 sec−1, the larger the Z value the finer became the dynamically recrystallized grain, and hence the value of Z nearly equal to 1012 sec−1 was the optimum deformation condition for the grain refinement by dynamic recrystallization. Furthermore, it was shown that there was a quantitative relationship between the dynamically recrystallized grain diameter (D) and the logarithm of Z as follows: D−1(μm−1)=−0.054+0.008logZ.
According to the results by transmission electron microscopy, it could be deduced that the mechanism of the dynamic recrystallization was based on the formation of recrystallized nuclei by bulging the localized area of the grain boundaries.
