C. Structural Observations
1. Microstructure analyses
The typical microstructure of the specimens before
and after deformation is taken from previous study.[4]
Figure 5a shows the microstructure before deformation.
The large and elongated grains are attributed to the
thermomechanical treatment of the as-received DSS,
which contains solely of a-ferrite (white phase).
Figure 5b shows the microstructure of a specimen after
compression for 0.2 strain, which yields fine grains with
an average size of approximately 3 lm.
Figure 6 shows the appearance of specimen before
and after SPC at 1 9 104 s1 strain rate and 1223 K
(950 C). The specimen is superplastically compressed
without cracks.
2. Carburized microstructure and layer thickness
Figure 7 shows the cross-sectional views of the
substrate carburized at 1 9 104 s1 and different temperatures.
From the figure, a thick, uniform, smooth
and dense morphology of carburized layer was formed
on the surface of the carburized specimen.