OCCURRENCE OF DYNAMIC RECRYSTALLIZATION IN FERRITIC IRON

The occurrence of dynamic recrystallization in ferritic iron, which is a typical dynamic recovery-type material, was confirmed in the presen t study using a Ti-added interstitial-free (IF) steel. The specimens w ere hot-compressed at various strain rates at various temperatures wit hin the ferritic region and quenched immediately after compression. Eq uiaxed grains surrounded by clearly-etched boundaries appeared prefere ntially near the initial grain boundaries in the small Zener-Hollomon parameter (Z) deformations. Microtextural analysis by Kikuchiline meas urements in TEM or EBSP in SEM clearly showed that these equiaxed grai ns are dynamically recrystallized with both the high angle grain bound aries and the dislocation substructures inside. The fraction and the s ize of the dynamically recrystallized grains increased with decreasing strain rates or increasing deformation temperature, i.e., decreasing Z. Consequently, the condition where dynamic recrystallization of ferr ite occurred was expressed as, Z less than or equal to 10(11) s(-1) in the present material. Nevertheless, despite the occurrence of dynamic recrystallization, a large stress drop in stress-strain curves was no t observed. The size of the dynamically recrystallized grains was much larger than that of the subgrains formed under the same deformation c ondition, which suggests that the dynamically recrystallized grains gr ew immediately after they obtained mobile boundaries. The characterist ics of the dynamic recrystallization of ferrite were the inhomogeneity of recrystallization as well as the small drop in stress. Some of the initial grains were hardly recrystallized even in the small-Z deforma tion, which is presumably due to the initial orientation dependence of recrystallization in ferrite. The nucleation of dynamic recrystalliza tion in ferrite was explained an the basis of the introduction of inho mogeneous deformation microstructure with large local misorientations.