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

GTBL042-11 GTBL042-Callister-v3 October 4, 2007 11:59

2nd Revised Pages

418 • Chapter 11 / Phase Transformations

Figure 11.15

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©c1976 by

John Wiley & Sons,

New York.

Reprinted by

permission of John

Wiley & Sons, Inc.)

consists of ferrite and cementite phases, and thus diffusional processes are involved in

its formation. Bainite forms as needles or plates, depending on the temperature of the

transformation; the microstructural details of bainite are so fine that their resolution

is possible only using electron microscopy. Figure 11.17 is an electron micrograph

that shows a grain of bainite (positioned diagonally from lower left to upper right); it

is composed of a ferrite matrix and elongated particles of Fe 3 C; the various phases in

Time (s)

Temperature (

°C)

Temperature (

°F)

110102 103 104

1000

1200

1400

1600

500

600

700

800

A

A

+

A C

P

Eutectoid temperature

900

A

+

P

Figure 11.16

Isothermal

transformation

diagram for a 1.13

wt% C iron–carbon

alloy: A, austenite; C,

proeutectoid

cementite; P, pearlite.

[Adapted from H.

Boyer (Editor),Atlas

of Isothermal

Transformation and

Cooling

Transformation

Diagrams, American

Society for Metals,

1977, p. 33.]