Callister - An introduction - 8th edition

10.5 Isothermal Transformation Diagrams • 359
1 s
1 min
1 h
1 day
A
727°C
Austenite (stable)
Eutectoid
temperature
1400
700
Ferrite
Coarse pearlite
Temperature (°C)
600
B
C
D
Fine pearlite
Fe 3 C
1200
Temperature (°F)
1000
500
Austenite → pearlite
transformation
Denotes that a transformation
is occurring
1 10 10 2 10 3 10 4 10 5
Time (s)
Figure 10.14 Isothermal transformation diagram for a eutectoid iron–carbon alloy, with
superimposed isothermal heat treatment curve (ABCD). Microstructures before, during,
and after the austenite-to-pearlite transformation are shown. [Adapted from H. Boyer
(Editor), Atlas of Isothermal Transformation and Cooling Transformation Diagrams,
American Society for Metals, 1977, p. 28.]
800
fine pearlite
carbon diffusion rate decreases, and the layers become progressively thinner. The
thin-layered structure produced in the vicinity of 540C is termed fine pearlite; this
is also indicated in Figure 10.14. To be discussed in Section 10.7 is the dependence
of mechanical properties on lamellar thickness. Photomicrographs of coarse and
fine pearlite for a eutectoid composition are shown in Figure 10.15.
Figure 10.15
Photomicrographs of
(a) coarse pearlite
and (b) fine pearlite.
3000. (From K. M.
Ralls et al., An
Introduction to
Materials Science
and Engineering,
p. 361. Copyright
©1976 by John Wiley
& Sons, New York.
Reprinted by
permission of John
Wiley & Sons, Inc.)
(a)
10 m (b)
10 m