Civil Engineering Reference
In-Depth Information
8.3.4 EAF Microstructure
In the following sections, various EAF micrographs are compared to the as-
received material and to room temperature deformation micrographs in order to
gain a better understanding of material deformation during EAF. The mechani-
cal results that generated these specimens are detailed in Appendix B and will be
noted in the below sections. Additional micrographs for the below results can be
seen in Appendix C and will be noted in the text.
8.3.4.1 Stationary Electrical Square Wave Current Application
To examine the influence of an applied electrical square wave without any defor-
mation, a test was performed where 500 A was passed through the sample every
60 s for the duration of 1 s. This square wave was applied to the specimen for nine
minutes which equates to nine electrical pulses (2.25
×
10
6
J/
Ω
). The micrograph
for orientation 1 is given in Fig. C.12 of Appendix C where a visual analysis sug-
gests no alterations to the microstructure when it is compared to the as-received
material.
This sample was compared to the as-received material as no deformation was
imposed. The average grain size for Sample 4 in orientation 1 is 6.78 µm with a
standard deviation of 2.13 µm. From the statistical analysis, the visual results are
confirmed in that the mean grain size and variance are equal.
The micrograph for orientation 2 is shown in Fig. C.13 where the average grain
size is 7.01 µm with a standard deviation of 2.22 µm.
From a visual inspection, there appears to be no difference as compared to the
as-received material in this orientation; however, the statistical analysis suggests
that the means are not equal. However, the Levene/Bartlett tests suggest that the
variances of the images are equivalent. The grain size in orientation 2 is slightly
larger as compared to the as-received material, and the reason for this may be due
to a temperature rise of the material which allowed for a slight amount of grain
growth which could have been favored in this orientation. Yet, there is no indica-
tion of a direct electrical effect on the material's grain size under stationary test-
ing. From the mechanical testing of these samples after electrical treatment, it
was concluded that stationary electrical treatment did not significantly alter the
mechanical response. This is confirmed from this microstructure analysis as the
material after electrical treatment is mostly equivalent to the as-received mate-
rial at this level of analysis. However, some dislocation annihilation may have
occurred to the as-received material due to the applied electrical current. This
type of analysis would need an additional study to quantify the dislocation density
before and after electrical treatment. As a result of the grain sizes being mostly
equal (orientation 2 is slightly larger in equivalent average grain size), any would
be attributed to the annihilation of dislocations or a change in dislocation density
within the material's lattice.
