GTBL042-10 GTBL042-Callister-v2 August 13, 2007 18:16
392 • Chapter 10 / Phase DiagramsConcentration of alloying elements (wt%)Eutectoid temperature (°C)Eutectoid temperature (°F)024 6810121410001200140016001800200022002400600800Ti
Mo Si WCrMn10001200NiFigure 10.38 The dependence of
eutectoid temperature on alloy
concentration for several alloying
elements in steel. (From Edgar C. Bain,
Functions of the Alloying Elements in
Steel,American Society for Metals,
1939, p. 127.)Concentration of alloying elements (wt%)Eutectoid composition (wt% C)024681012TiMo
W MnSiCrNi(^014)
0.2
0.4
0.6
0.8
Figure 10.39 The dependence of eutectoid
composition (wt% C) on alloy concentration for
several alloying elements in steel. (From Edgar
C. Bain,Functions of the Alloying Elements in
Steel,American Society for Metals, 1939, p. 127.)
relative fractions of pearlite and the proeutectoid phase that form. Steels are nor-
mally alloyed for other reasons, however—usually either to improve their corrosion
resistance or to render them amenable to heat treatment (see Section 14.6).
SUMMARY
Phase Equilibria
One-Component (or Unary) Phase Diagrams
Binary Phase Diagrams
Interpretation of Phase Diagrams
Equilibrium phase diagrams are a convenient and concise way of representing
the most stable relationships between phases in alloy systems. This discussion be-
gan by considering the unary (or pressure–temperature) phase diagram for a one-
component system. Solid-, liquid-, and vapor-phase regions are found on this type
of phase diagram. For binary systems, temperature and composition are variables,
whereas external pressure is held constant. Areas, or phase regions, are defined on
these temperature-versus-composition plots within which either one or two phases
exist. For an alloy of specified composition and at a known temperature, the phases
present, their compositions, and relative amounts under equilibrium conditions may
be determined. Within two-phase regions, tie lines and the lever rule must be used
for phase composition and mass fraction computations, respectively.