Civil Engineering Reference
In-Depth Information
Fig. 8.25
Microstructure of
EAF (800 A; 0.5-60 s) test
(sample 14) in orientation
1 at L1
two-sample t test equates these three average grain sizes, it is clearly visible that
the shape varies along the length of the test specimen. Again, this is physically due
to the thermal gradients present during EAF, which results in localized strains that
vary along the length as compared to uniform room temperature deformation. It is
also noted that there is a lower number of twin boundaries present in these micro-
graphs as compared to the room temperature deformation micrograph.
Upon comparing these microstructure results (orientation 1) to the test
deformed at room temperature in orientation 1, it is statistically observed that the
mean is not equivalent even when comparing the results at L1. This is mainly a
result of the difference in strain of these regions. In the test deformed at room tem-
perature, the material strain is uniform throughout its gauge section until localized
necking occurs, whereas the EAF test displays diffuse necking. Last, it is noted
that the variances were statistically equivalent to the test deformed at room tem-
perature (Sample 2) even though the grain size was not. Last, the EAF (800 sA;
0.5-60 s) test displayed a reduced amount of material twinning which may be a
result of the applied electrical current aiding in deformation by a temperature rise
(Joule heating) and/or by direct electrical effects.
A similar analysis was conducted for orientation 2, and the micrographs are
presented in Figs. C.16, C.17 and C.18 for the EAF (800 A; 0.5-60 s) test. From
a visual analysis, it is evident that a microstructure gradient exists within the test
sample for this orientation as well. This is seen where the grains become less equi-
axed from L3 toward L1 and the grain boundaries are more jagged indicating a
greater amount of strain. The average grain size for the EAF (800 A; 0.5-60 s)
test in orientation 2 at L3 is 5.7 µm with a standard deviation of 1.66 µm. For the
same test and orientation at L2, the average grain size is 5.69 µm with a standard
deviation of 1.79 µm, and L1 has a grain size of 6.96 µm with a standard devia-
tion of 2.40 µm. From the statistical analysis, the average grain size of L2 (Sample
15) and L3 (Sample 16) was equivalent, but L1 (Sample 14) was different from
both L2 and L3. However, the variances for L1-L3 were equal. Again, it is noted
