the bowing out of OAGBs appeared (Fig. 4(b)). With decreasing deformation
temperature to 600°C, a few small grains about 3.2 μm
were observed, mainly at the OAGBs (Fig. 4(c)). When the
overcooled austenite was deformed at 550°C, more small
grains about 3.8 μm were mostly located along the OAGBs,
and a few fresh grains were formed in the deformed original
austenite grains (Fig. 4(d)).
The microstructure before deformation in the temperature
range of 550–700°C is austensite due to the high cooling
rate of 50°C/s, which inhibits the decomposition of
austenite. The as-reheated microstructure at 900°C is also
austensite after warm deformation at various deformation
temperatures. The austensite grain boundaries at 900°C are
characterized by a pancaked morphology, which results
from warm deformation at low temperature. Meanwhile, the
change in austenite grain boundaries at 900°C with different
deformation temperature is in accordance with the typical
recrystallization characteristics of austenite.16) Therefore,
the austenite experienced restoration rather than decomposition
during reheating process after warm deformation, which
may involve meta-dynamic recrystallization, static recovery
or static recrystallization.17,18)
Figure 3 shows that there is no decrease in flow stress with