Page 383 - Materials Science and Engineering An Introduction

Questions and Problems • 355

(a) How many kilograms of proeutectoid ferrite (a) What is the eutectoid temperature of this alloy?
form? (b) What is the eutectoid composition?
(b) How many kilograms of eutectoid ferrite form? (c) What is the proeutectoid phase?
(c) How many kilograms of cementite form? Assume that there are no changes in the positions
9.71 Compute the maximum mass fraction of proeu- of other phase boundaries with the addition of W.
tectoid cementite possible for a hypereutectoid 9.81 A steel alloy is known to contain 93.65 wt% Fe,
iron–carbon alloy. 6.0 wt% Mn, and 0.35 wt% C.
9.72 Is it possible to have an iron–carbon alloy for (a) What is the approximate eutectoid tempera-
which the mass fractions of total cementite and ture of this alloy?
proeutectoid ferrite are 0.057 and 0.36, respec-
tively? Why or why not? (b) What is the proeutectoid phase when this
alloy is cooled to a temperature just below the
9.73 Is it possible to have an iron–carbon alloy for eutectoid?
which the mass fractions of total ferrite and pearlite
are 0.860 and 0.969, respectively? Why or why not? (c) Compute the relative amounts of the proeu-
tectoid phase and pearlite. Assume that there
9.74 Compute the mass fraction of eutectoid cementite are no alterations in the positions of other phase
in an iron–carbon alloy that contains 1.00 wt% C. boundaries with the addition of Mn.
9.75 Compute the mass fraction of eutectoid cementite
in an iron–carbon alloy that contains 0.87 wt% C.
FUNDAMENTALS OF ENGINEERING
9.76 The mass fraction of eutectoid cementite in an QUESTIONS AND PROBLEMS
iron–carbon alloy is 0.109. On the basis of this in-
formation, is it possible to determine the composi- 9.1FE Once a system is at a state of equilibrium, a
tion of the alloy? If so, what is its composition? If shift from equilibrium may result by alteration of
this is not possible, explain why. which of the following?
9.77 The mass fraction of eutectoid ferrite in an iron– (A) Pressure (C) Temperature
carbon alloy is 0.71. On the basis of this informa- (B) Composition (D) All of the above
tion, is it possible to determine the composition of 9.2FE A binary composition–temperature phase dia-
the alloy? If so, what is its composition? If this is gram for an isomorphous system is composed of
not possible, explain why.
regions that contain which of the following phases
9.78 For an iron–carbon alloy of composition 3 wt% and/or combinations of phases?
C–97 wt% Fe, make schematic sketches of the (A) Liquid
microstructure that would be observed for condi- (C) a
tions of very slow cooling at the following tem- (B) Liquid a (D) a, liquid, and liquid a
peratures: 1250 C (2280 F), 1145 C (2095 F), and 9.3FE From the lead–tin phase diagram (Figure 9.8),
700 C (1290 F). Label the phases and indicate which of the following phases/phase combinations
their compositions (approximate). is present for an alloy of composition 46 wt%
9.79 Often, the properties of multiphase alloys may Sn–54 wt% Pb that is at equilibrium at 44 C?
be approximated by the relationship (A) a (C) b liquid
E (alloy) = E a V a + E b V b (9.24) (B) a b (D) a b liquid
where E represents a specific property (modulus 9.4FE For a lead–tin alloy of composition 25 wt%
of elasticity, hardness, etc.), and V is the volume Sn–75 wt% Pb, select from the following list the
fraction. The subscripts a and b denote the exist- phase(s) present and their composition(s) at 200 C.
ing phases or microconstituents. Use this relation- (The Pb–Sn phase diagram appears in Figure 9.8.)
ship to determine the approximate Brinell hard- (A) a 17 wt% Sn–83 wt% Pb; L 55.7 wt%
ness of a 99.75 wt% Fe–0.25 wt% C alloy. Assume Sn–44.3 wt% Pb
Brinell hardnesses of 80 and 280 for ferrite and
pearlite, respectively, and that volume fractions (B) a 25 wt% Sn–75 wt% Pb; L 25 wt%
may be approximated by mass fractions. Sn–75 wt% Pb
(C) a 17 wt% Sn–83 wt% Pb; b 55.7 wt%
The Influence of Other Alloying Elements Sn–44.3 wt% Pb
9.80 A steel alloy contains 95.7 wt% Fe, 4.0 wt% W, (D) a 18.3 wt% Sn–81.7 wt% Pb; b 97.8 wt%
and 0.3 wt% C. Sn–2.2 wt% Pb