Civil Engineering Reference
In-Depth Information
80%
m=
0.5
Top and bottom dies
temperature:
200ºC
20ºC
Thermal test
60%
m=
0.3
40%
Ring temperature:
~
300ºC
20%
m=
0.2
0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
m=
0.1
20%
-
Ring height reduction [%]
Fig. 9.33
Friction calibration curves for tests at room temperature and at an elevated tempera-
ture [
13
,
14
]. The friction calibration curves were tested at room temperature (20 °C) and at an
elevated temperature that was respective of what would be reached during an EAF test (300 °C)
Initial
Stroke 1
Stroke 2
Fig. 9.34
Initial and deformed ring compression samples [
13
,
14
]. Shown is the initial unde-
formed ring compression sample, as well a sample that has been deformed to the two different
strokes used for testing
sparks. After this, the ring specimens were compressed at a rate of 6.35 mm/min
to strokes of 1 mm and 1.3 mm. Figure
9.34
displays a ring specimen prior to
deformation, deformed to a stroke of 1 mm (Stroke 1), and deformed to a stroke of
1.3 mm (Stroke 2).
For each stroke, three electrical conditions were evaluated: (i) conventional
forming (no electricity), (ii) a current density of 25 A/mm
2
(333 Amps), and (iii)
a current density of 35 A/mm
2
(467 Amps). The voltage across the specimens was
measured at the beginning of the tests. Specifically, the voltage for a current den-
sity of 25 A/mm
2
was 110 mV, and the voltage for a current density of 35 A/mm
2
was 160 mV. From Perkins et al. [
20
] where the same stainless steel alloy was
tested under electrical conditions, the “electrical threshold” (i.e., minimum current
density where enhanced formability effects are first observed) was determined to
