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Callister - An introduction - 8th edition

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334 • Chapter 9 / Phase Diagrams<br />

9.20<br />

W r C¿ 0 0.022<br />

0.74<br />

For a hypoeutectoid Fe–C alloy, the mass fraction<br />

of pearlite (per Figure 9.31)<br />

326<br />

9.21<br />

W a¿ 0.76 C¿ 0<br />

0.74<br />

For a hypoeutectoid Fe–C alloy, the mass fraction<br />

of proeutectoid ferrite phase (per Figure 9.31)<br />

326<br />

9.22<br />

W p 6.70 C¿ 1<br />

5.94<br />

For a hypereutectoid Fe–C alloy, the mass fraction<br />

of pearlite (per Figure 9.31)<br />

328<br />

9.23<br />

W Fe3 C' C¿ 1 0.76<br />

5.94<br />

For a hypereutectoid Fe–C alloy, the mass fraction<br />

of proeutectoid Fe 3 C (per Figure 9.31)<br />

328<br />

List of Symbols<br />

Symbol<br />

Meaning<br />

C (Gibbs phase rule) Number of components in a system<br />

C 0<br />

Composition of alloy (in terms of one of the components)<br />

Composition of a hypoeutectoid alloy (in weight<br />

percent carbon)<br />

C¿ 1<br />

Composition of a hypereutectoid alloy (in weight<br />

percent carbon)<br />

F<br />

Number of externally controlled variables that must be<br />

specified to completely define the state of a system<br />

N<br />

Number of noncompositional variables for a system<br />

P, Q, R Lengths of tie–line segments<br />

P (Gibbs phase rule) Number of phases present in a given system<br />

v a , v b<br />

Volumes of and phases<br />

r a , r b<br />

Densities of and phases<br />

C¿ 0<br />

Processing Structure<br />

Processing/Structure/Properties/Performance Summary<br />

For iron–carbon alloys (i.e., steels), an understanding of microstructures that develop<br />

during relatively slow rates of cooling (i.e., pearlite and a proeutectoid phase)<br />

is facilitated by the iron–iron carbide phase diagram. Other concepts in this chapter<br />

were presented as a prelude to the <strong>introduction</strong> of this diagram—the concepts<br />

of a phase, phase equilibrium, metastability, and the eutectoid reaction. In Chapter<br />

10 we explore yet other microstructures that form when iron–carbon alloys are<br />

cooled from elevated temperatures at more rapid rates. These concepts are summarized<br />

in the following diagram:<br />

Eutectoid<br />

reaction<br />

(Chapter 9)<br />

Phase Metastable vs. Iron–iron carbide<br />

equilibria equilibrium phase diagram<br />

(Chapter 9) states (Chapter 9)<br />

(Chapter 9)<br />

Development of microstructure<br />

(pearlite and a proeutectoid<br />

phase)<br />

(Chapter 9)<br />

Development of other<br />

microstructures<br />

(Chapter 10)

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