GTBL042-11 GTBL042-Callister-v3 October 4, 2007 11:59
2nd Revised PagesLearning Objectives
After careful study of this chapter you should be able to do the following:
1.Make a schematic fraction transformation-
versus-logarithm of time plot for a typical solid–
solid transformation; cite the equation that
describes this behavior.
2.Briefly describe the microstructure for each of
the following microconstituents that are found in
steel alloys: fine pearlite, coarse pearlite,
spheroidite, bainite, martensite, and tempered
martensite.
3.Cite the general mechanical characteristics for
each of the following microconstituents: fine
pearlite, coarse pearlite, spheroidite, bainite,
martensite, and tempered martensite. Now, in
terms of microstructure (or crystal structure),
briefly explain these behaviors.
4.Given the isothermal transformation (or
continuous cooling transformation) diagram for
some iron–carbon alloy, design a heattreatment that will produce a specified
microstructure.
5.Using a phase diagram, describe and explain the
two heat treatments that are used to
precipitation harden a metal alloy.
6.Make a schematic plot of room-temperature
strength (or hardness) versus the logarithm of
time for a precipitation heat treatment at
constant temperature. Explain the shape of this
curve in terms of the mechanism of precipitation
hardening.- Schematically plot specific volume versus
temperature for crystalline, semicrystalline, and
amorphous materials, noting glass transition and
melting temperatures.
8.List four characteristics or structural components
of a polymer that affect both its melting and glass
transition temperatures.
11.1 INTRODUCTION
Mechanical and other properties of many materials depend on their microstructures,
which are often produced as a result of phase transformations. In the first portion
of this chapter we discuss the basic principles of phase transformations. Next, we
address the role these transformations play in the development of microstructure for
iron–carbon, as well as other alloys, and how the mechanical properties are affected
by these microstructural changes. Finally, we treat crystallization, melting, and glass
transition transformations in polymers.Phase Transformations in Metals
One reason for the versatility of metallic materials lies in the wide range of mechan-
ical properties they possess, which are accessible to management by various means.
Three strengthening mechanisms were discussed in Chapter 8—namely, grain size re-
finement, solid-solution strengthening, and strain hardening. Additional techniques
are available wherein the mechanical properties are reliant on the characteristics of
the microstructure.
The development of microstructure in both single- and two-phase alloys ordinar-
ily involves some type of phase transformation—an alteration in the number and/or
character of the phases. The first portion of this chapter is devoted to a brief discus-
sion of some of the basic principles relating to transformations involving solid phases.
Inasmuch as most phase transformations do not occur instantaneously, consideration
transformation rate is given to the dependence of reaction progress on time, or thetransformation rate.
This is followed by a discussion of the development of two-phase microstructures for
iron–carbon alloys. Modified phase diagrams are introduced that permit determina-
tion of the microstructure that results from a specific heat treatment. Finally, other