Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Occurrence of Dynamic Recrystallization in Ferritic Iron
Nobuhiro TsujiYukihiro MatsubaraYoshihiro SaitoTadashi Maki
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1998 Volume 62 Issue 10 Pages 967-976

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Abstract

The occurrence of dynamic recrystallization in ferritic iron, which is a typical dynamic recovery-type material, was confirmed in the present study using a Ti-added interstitial-free (IF) steel. The specimens were hot-compressed at various strain rates at various temperatures within the ferritic region and quenched immediately after compression. Equiaxed grains surrounded by clearly-etched boundaries appeared preferentially near the initial grain boundaries in the small Zener-Hollomon parameter (Z) deformations. Microtextural analysis by Kikuchi-line measurements in TEM or EBSP in SEM clearly showed that these equiaxed grains are dynamically recrystallized with both the high angle grain boundaries and the dislocation substructures inside. The fraction and the size 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 ferrite occurred was expressed as, Z≤1011 s−1 in the present material. Nevertheless, despite the occurrence of dynamic recrystallization, a large stress drop in stress-strain curves was not observed. The size of the dynamically recrystallized grains was much larger than that of the subgrains formed under the same deformation condition, which suggests that the dynamically recrystallized grains grew immediately after they obtained mobile boundaries. The characteristics 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 deformation, which is presumably due to the initial orientation dependence of recrystallization in ferrite. The nucleation of dynamic recrystallization in ferrite was explained on the basis of the introduction of inhomogeneous deformation microstructure with large local misorientations.

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