Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-10 GTBL042-Callister-v2 August 13, 2007 18:16

10.20 Development of Microstructure in Iron–Carbon Alloys • 389

Composition (wt % C)

C 1

z'





+

0 1.0 2.0

Proeutectoid

Fe 3 C

Temperature (

°C)

+ Fe 3 C







+ Fe 3 C

     





z

g

h

O i

(^1100) P
900
800
700
600
500
400
Eutectoid Fe 3 C
Fe 3 C
1000
Pearlite
Figure 10.36 Schematic
representations of the
microstructures for an
iron–carbon alloy of
hypereutectoid composition
C 1 (containing between 0.76
and 2.14 wt% C), as it is
cooled from within the
austenite phase region to
below the eutectoid
temperature.
the temperature is lowered through the eutectoid to pointi, all remaining austenite
of eutectoid composition is converted into pearlite; thus, the resulting microstructure
consists of pearlite and proeutectoid cementite as microconstituents (Figure 10.36).
In the photomicrograph of a 1.4 wt% C steel (Figure 10.37), note that the proeutectoid
cementite appears light. Since it has much the same appearance as proeutectoid
Proeutectoid
cementite
Pearlite
Figure 10.37
Photomicrograph of a
1.4 wt% C steel having
a microstructure
consisting of a white
proeutectoid cementite
network surrounding
the pearlite colonies.
1000 ×. (Copyright
1971 by United States
Steel Corporation.)