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

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

2nd Revised Pages

424 • Chapter 11 / Phase Transformations

Time (s)

Temperature (

°C)

Temperature (

°F)

110102 103 104 105 106

200

400

800

600

1000

1200

1400

Eutectoid temperature

A

A

A + F F + P

A + B

M + A

M(start)

M(50%)

M(90%)

50% B

100 M

0

200

300

400

500

600

700

800

A + F

+ P

Figure 11.24

Isothermal

transformation

diagram for an alloy

steel (type 4340): A,

austenite; B, bainite;

P, pearlite; M,

martensite; F,

proeutectoid ferrite.

[Adapted from H.

Boyer (Editor),Atlas

of Isothermal

Transformation and

Cooling

Transformation

Diagrams, American

Society for Metals,

1977, p. 181.]

Concept Check 11.2

Cite two major differences between martensitic and pearlitic transformations.

[The answer may be found at http://www.wiley.com/college/callister (Student Companion Site).]

EXAMPLE PROBLEM 11.2

Microstructural Determinations for Three Isothermal

Heat Treatments

Using the isothermal transformation diagram for an iron–carbon alloy of eu-

tectoid composition (Figure 11.23), specify the nature of the final microstruc-

ture (in terms of microconstituents present and approximate percentages) of

a small specimen that has been subjected to the following time–temperature

treatments. In each case assume that the specimen begins at 760◦C (1400◦F)

and that it has been held at this temperature long enough to have achieved a

complete and homogeneous austenitic structure.

(a)Rapidly cool to 350◦C (660◦F), hold for 10^4 s, and quench to room temper-

ature.

(b)Rapidly cool to 250◦C (480◦F), hold for 100 s, and quench to room temper-

ature.