Question 3
(a) Figure Q3 below shows the Iron-Iron Carbide phase diagram. Consider a steel with a 99.0
wt% Fe 1.0 wt% C composition. Consider cooling of this steel from high temperature
(1600°C) under equilibrium conditions and answer the following:
i. At what temperature will the steel be completely solidified, and identify this solid
phase?
[2]
ii.
iii.
iv.
V.
[1]
At what temperature will Cementite begin to form in the solid steel?
Sketch and describe the microstructure, at a temperature just below the eutectoid, and
state whether this is a Hypo-Eutectoid or Hyper-Eutectoid steel.
Calculate the wt% of both Pearlite and pro-eutectoid Cementite, at a temperature just
below the eutectoid.
[4]
[3]
Calculate the wt% of both a and Cementite phases, at a temperature just below the
eutectoid.
[3]
Temperature (°C)
1600
1538°C
1493°C
1400
$\delta$
L
2500
1394°C
$\gamma$+L
1200
1147°C
$\gamma$, Austenite
2.14
4.30
2000
1000
912°C
$\gamma$ + $Fe_3C$
800
$\alpha$
+
$\gamma$
600
0.76
0.022
$\alpha$, Ferrite
$\alpha$ + $Fe_3C$
727°C
1500
Cementite ($Fe_3C$)
1000
400
0
(Fe)
1
2
3
4
5
6
6.70
Composition (wt% C)
Figure Q3
Temperature (°F)
