Effect of initial grain size of austenite on hot-deformed structure of Ni-30Fe alloy

Abstract

The microstructural evolutions of Ni-30Fe alloys during hot deformation are investigated. Hot-deformed structures of Ni-30Fe alloys with initial austenite grain sizes of 20 and 140 m are examined under various compressive strains and deformation temperatures. As the initial austenite grain size decreases, dynamic recrystallization (DRX) occurs at lower compressive strain and lower deformation temperature. At deformation temperatures where dynamic recovery occurs instead of the DRX, hot-deformed structures consist of recovered elongated grains until fine-equiaxed grains are evolved by geometric DRX. Critical compressive strain for the geometric DRX decreases with the decrease of initial austenite grain size. Geometric DRX is evolved by the impingement of serrated grain boundaries. The decrease of initial grain size is considered to reduce the critical compressive strain needed for the impingement of serrated grain boundaries. The changes in the effective thickness of austenite grain according to the compressive deformation are examined and the effects of the restoration processes on the effective thickness of austenite grain are discussed.

Dependency of Recrystallization Mechanism to the Initial Grain Size

“…Previous work on Al alloys, [16,17] Ni-30Fe, [37] and stainless steel [11] have shown occurrence of CDRX in materials with a very small initial grain size. In the present work, there is some evidence to support a change from DDRX to CDRX by the microstructure and substructure analysis of the fine-and coarse-grain materials.…”

Effect of hot working on dynamic recrystallisation study of as-cast austenitic stainless steel

“…However, at a critical value, the finer grain size ($8 mm) showed almost no change with increasing Z; for the coarse grain size (Z35 mm), there was no change in behaviour over the entire Z range. Suh et al [13] investigated the microstructural evolutions of Ni-30Fe alloys with initial austenite grain sizes of 20 and 140 mm under various hot deformation conditions. They observed that the critical strain for the evolution of geometric DRX decreases according to the decrease of initial grain size, and the DRX region in the microstructural evolution map extends to lower temperature and lower compressive strain as the initial grain size decreases.…”

Effect of Initial Grain Size on the Dynamic Recrystallization Behaviours of Austenite

“…6d) consisted of small equiaxed grains which replaced all of the initial structure. Such a decrease in the initial grain size has been proposed to change the DRX mechanism from discontinuous (DDRX) to continuous (CDRX) [6][7][8]. This potential difference in DRX mechanism of fine and coarse grain materials also appears to have a moderate effect on the recrystallized grain size.…”