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

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

2nd Revised Pages

456 • Chapter 11 / Phase Transformations

Time (s)

Temperature (

°C)

Temperature (

°F)

110102 103 104 105 106

200

400

600

800

1000

1200

1400

1600

0

100

200

300

400

500

600

700

800

900

A

A

A + C

A + P

A + B

B

50 %

M(start)

M(50%)

M(90%)

P

Figure 11.49 Isothermal

transformation diagram for a 1.13

wt% C iron–carbon alloy: A,

austenite; B, bainite; C,

proeutectoid cementite; M,

martensite; P, pearlite. [Adapted

from H. Boyer (Editor),Atlas of

Isothermal Transformation and

Cooling Transformation

Diagrams, American Society for

Metals, 1977, p. 33.]

11.13Make a copy of the isothermal transforma-

tion diagram for a 1.13 wt% C iron–carbon

alloy (Figure 11.49), and then on this diagram

sketch and label time–temperature paths to

produce the following microstructures:

(a)6.2% proeutectoid cementite and 93.8%

coarse pearlite

(b)50% fine pearlite and 50% bainite

(c)100% martensite

(d)100% tempered martensite

Continuous Cooling Transformation Diagrams

11.14Figure 11.50 shows the continuous cooling

transformation diagram for a 0.35 wt% C

iron–carbon alloy. Make a copy of this figure

and then sketch and label continuous cool-

ing curves to yield the following microstruc-

tures:

(a)Fine pearlite and proeutectoid ferrite

(b)Martensite and proeutectoid ferrite

(c)Martensite, fine pearlite, and proeutec-

toid ferrite

11.15Cite two important differences between con-

tinuous cooling transformation diagrams for

plain carbon and alloy steels.

11.16Name the microstructural products of 4340

alloy steel specimens that are first com-

pletely transformed to austenite, then cooled

to room temperature at the following

rates:

(a)0.005◦C/s,

(b)0.05◦C/s,

(c)0.5◦C/s,

(d) 5 ◦C/s.

11.17Briefly describe the simplest continuous cool-

ing heat treatment procedure that would be

used in converting a 4340 steel from one mi-

crostructure to another.

(a)(Martensite + ferrite + bainite) to

(martensite+ferrite+pearlite+bai-

nite)

(b)(Martensite + ferrite + bainite) to

spheroidite

(c)(Martensite+bainite+ferrite) to tem-

pered martensite

Mechanical Behavior of Iron–Carbon Alloys

Tempered Martensite

11.18Briefly explain why fine pearlite is harder and

stronger than coarse pearlite, which in turn is

harder and stronger than spheroidite.