Page 266 - Materials Science and Engineering An Introduction

238 • Chapter 7 / Dislocations and Strengthening Mechanisms

Figure 7.22 The influence of annealing Annealing temperature (°F)
temperature (for an annealing time of 1 h) 400 600 800 1000 1200
on the tensile strength and ductility of 600 60
a brass alloy. Grain size as a function of
annealing temperature is indicated. Grain Tensile strength
structures during recovery, recrystalliza- 50
tion, and grain growth stages are shown 500
schematically.
(Adapted from G. Sachs and K. R. Van Horn, 40
Practical Metallurgy, Applied Metallurgy Tensile strength (MPa) Ductility (%EL)
and the Industrial Processing of Ferrous and
Nonferrous Metals and Alloys, 1940. 400 30
Reproduced by permission of ASM
International, Materials Park, OH.) Ductility

20
300
Recovery Recrystallization Grain growth
Cold-worked
and recovered
grains

New
0.040 grains
Grain size (mm) 0.030
0.020
0.010

100 200 300 400 500 600 700
Annealing temperature (°C)

Plastic deformation operations are often carried out at temperatures above the re-
crystallization temperature in a process termed hot working, described in Section 11.4.
The material remains relatively soft and ductile during deformation because it does not
strain harden, and thus large deformations are possible.

Figure 7.23 The variation of recrystallization 900
temperature with percent cold work for iron. For 1600
deformations less than the critical (about
5%CW), recrystallization will not occur. 800 1400
Recrystallization temperature ( C) 600 1200 Recrystallization temperature ( F)
700

1000
500

400 800

300 600
0 10 20 30 40 50 60 70
Percent cold work
Critical
deformation