11.

11 The principal difference between wrought and cast alloys is as follows: wrought alloys are ductile
enough so as to be hot- or cold-worked during fabrication, whereas cast alloys are brittle to the
degree that shaping by deformation is not possible and they must be fabricated by casting.

11.12 Both brasses and bronzes are copper-based alloys. For brasses, the principal alloying element is
zinc, whereas the bronzes are alloyed with other elements such as tin, aluminum, silicon, or nickel.

11.13 Rivets of a 2017 aluminum alloy must be refrigerated before they are used because, after being
solution heat treated, they precipitation harden at room temperature. Once precipitation hardened,
they are too strong and brittle to be driven.

11.14 Strengthening of a 3003 aluminum alloy is accomplished by cold working. Welding a structure of a
cold-worked 3003 alloy will cause it to experience recrystallization, and a resultant loss of strength.

11.15 The chief difference between heat-treatable and nonheat-treatable alloys is that heat-treatable
alloys may be strengthened by a heat treatment wherein a precipitate phase is formed (precipitation
hardening) or a martensitic transformation occurs. Nonheat-treatable alloys are not amenable to
strengthening by such treatments.

11.16 This question asks us for the distinctive features, limitations, and applications of several alloy
groups.
Titanium Alloys
Distinctive features: relatively low densities, high melting temperatures, and high strengths
are possible.
Limitation: because of chemical reactivity with other materials at elevated temperatures,
these alloys are expensive to refine.
Applications: aircraft structures, space vehicles, and in chemical and petroleum industries.
Refractory Metals
Distinctive features: extremely high melting temperatures; large elastic moduli, hardnesses,
and strengths.
Limitation: some experience rapid oxidation at elevated temperatures.
Applications: extrusion dies, structural parts in space vehicles, incandescent light filaments,
x-ray tubes, and welding electrodes.
Superalloys
Distinctive features: able to withstand high temperatures and oxidizing atmospheres for long
time periods.

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 Applications: aircraft turbines, nuclear reactors, and petrochemical equipment.
Noble Metals
Distinctive features: highly resistant to oxidation, especially at elevated temperatures; soft
and ductile.
Limitation: expensive.
Applications: jewelry, dental restoration materials, coins, catalysts, and thermocouples.

11.17 The advantages of cold working are:

1) A high quality surface finish.
2) The mechanical properties may be varied.
3) Close dimensional tolerances.
The disadvantages of cold working are:
1) High deformation energy requirements.
2) Large deformations must be accomplished in steps, which may be expensive.
3) A loss of ductility.
The advantages of hot working are:
1) Large deformations are possible, which may be repeated.
2) Deformation energy requirements are relatively low.
The disadvantages of hot working are:
1) A poor surface finish.
2) A variety of mechanical properties is not possible.

11.18 (a) The advantages of extrusion over rolling are as follows:

1) Pieces having more complicated cross-sectional geometries may be formed.
2) Seamless tubing may be produced.
(b) The disadvantages of extrusion over rolling are as follows:
1) Nonuniform deformation over the cross-section.
2) A variation in properties may result over the cross-section of an extruded piece.

11.19 Four situations in which casting is the preferred fabrication technique are:
1) For large pieces and/or complicated shapes.
2) When mechanical strength is not an important consideration.
3) For alloys having low ductilities.
4) When it is the most economical fabrication technique.

11.20 This question asks us to compare sand, die, investment, and continuous casting techniques.

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 For sand casting, sand is the mold material, a two-piece mold is used, ordinarily the surface
finish is not an important consideration, the sand may be reused (but the mold may not), casting
rates are low, and large pieces are usually cast.
For die casting, a permanent mold is used, casting rates are high, the molten metal is
forced into the mold under pressure, a two-piece mold is used, and small pieces are normally cast.
For investment casting, a single-piece mold is used, which is not reusable; it results in high
dimensional accuracy, good reproduction of detail, and a fine surface finish; and casting rates are
low.
For continuous casting, at the conclusion of the extraction process, the molten metal is
cast into a continuous strand having either a rectangular or circular cross-section; these shapes are
desirable for subsequent secondary metal-forming operations. The chemical composition and
mechanical properties are relatively uniform throughout the cross-section.

11.21 (a) Some of the advantages of powder metallurgy over casting are as follows:
1) It is used for alloys having high melting temperatures.
2) Better dimensional tolerances result.
3) Porosity may be introduced, the degree of which may be controlled (which is desirable in some
applications such as self-lubricating bearings).
(b) Some of the disadvantages of powder metallurgy over casting are as follows:
1) Production of the powder is expensive.
2) Heat treatment after compaction is necessary.

11.22 This question asks for the principal differences between welding, brazing, and soldering.
For welding, there is melting of the pieces to be joined in the vicinity of the bond; a filler
material may or may not be used.
For brazing, a filler material is used which has a melting temperature in excess of about
425°C (800°F); the filler material is melted, whereas the pieces to be joined are not melted.
For soldering, a filler material is used which has a melting temperature less than about
425°C (800°F); the filler material is melted, whereas the pieces to be joined are not.

11.23 This problem asks that we specify and compare the microstructures and mechanical properties in
the heat-affected weld zones for 1080 and 4340 alloys assuming that the average cooling rate is
10°C/s. Figure 10.18 shows the continuous cooling transformation diagram for an iron-carbon alloy
of eutectoid composition (1080), and, in addition, cooling curves that delineate changes in
microstructure. For a cooling rate of 10°C/s (which is less than 35°C/s) the resulting microstructure
will be totally pearlite--probably a reasonably fine pearlite. On the other hand, in Figure 10.19 is

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 shown the CCT diagram for a 4340 steel. From this diagram it may be noted that a cooling rate of
10°C/s produces a totally martensitic structure. Pearlite is softer and more ductile than martensite,
and, therefore, is most likely more desirable.

11.24 If a steel weld is cooled very rapidly, martensite may form, which is very brittle. In some situations,
cracks may form in the weld region as it cools.

11.25 Full annealing--Heat to between 15 and 40°C above the A line (if the concentration of carbon is
3
less than the eutectoid) or above the A line (if the concentration of carbon is greater than the
1
eutectoid) until the alloy comes to equilibrium; then furnace cool to room temperature. The final
microstructure is coarse pearlite.
Normalizing--Heat to between 55 and 85°C above the upper critical temperature until the specimen
has fully transformed to austenite, then cool in air. The final microstructure is fine pearlite.
Quenching--Heat to a temperature within the austenite phase region and allow the specimen to fully
austenitize, then quench to room temperature in oil or water. The final microstructure is martensite.
Tempering--Heat a quenched (martensitic) specimen, to a temperature between 450 and 650°C, for
the time necessary to achieve the desired hardness. The final microstructure is tempered
martensite.

11.26 Three sources of residual stresses in metal components are plastic deformation processes,
nonuniform cooling of a piece that was cooled from an elevated temperature, and a phase
transformation in which parent and product phases have different densities.
Two adverse consequences of these stresses are distortion (or warpage) and fracture.

11.27 This question asks that we cite the temperature range over which it is desirable to austenitize
several iron-carbon alloys during a normalizing heat treatment.
(a) For 0.20 wt% C, heat to between 890 and 920°C (1635 and 1690°F) since the A temperature is
3
835°C (1535°F).
(b) For 0.76 wt% C, heat to between 782 and 812°C (1440 and 1494°F) since the A temperature is
3
727°C (1340°F).
(c) For 0.95 wt% C, heat to between 840 and 870°C (1545 and 1600°F) since A is 785°C
cm
(1445°F).

11.28 We are asked for the temperature range over which several iron-carbon alloys should be
austenitized during a full-anneal heat treatment.

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 (a) For 0.25 wt% C, heat to between 845 and 870°C (1555 and 1600°F) since the A temperature is
3
830°C (1525°F).
(b) For 0.45 wt% C, heat to between 790 and 815°C (1450 and 1500°F) since the A temperature is
3
775°C (1425°F).
(c) For 0.85 wt% C, heat to between 742 and 767°C (1368 and 1413°F) since the A temperature is
1
727°C (1340°F).
(d) For 1.10 wt% C, heat to between 742 and 767°C (1368 and 1413°F) since the A temperature is
1
727°C (1340°F).

11.29 The purpose of a spheroidizing heat treatment is to produce a very soft and ductile steel alloy
having a spheroiditic microstructure. It is normally used on medium- and high-carbon steels, which,
by virtue of carbon content, are relatively hard and strong.

11.30 Hardness is a measure of a material's resistance to localized surface deformation, whereas

hardenability is a measure of the depth to which a ferrous alloy may be hardened by the formation of
martensite. Hardenability is determined from hardness tests.

11.31 The presence of alloying elements (other than carbon) causes a much more gradual decrease in
hardness with position from the quenched end for a hardenability curve. The reason for this effect is
that alloying elements retard the formation of pearlitic and bainitic structures which are not as hard
as martensite.

11.32 A decrease of austenite grain size will decrease the hardenability. Pearlite normally nucleates at
grain boundaries, and the smaller the grain size, the greater the grain boundary area, and,
consequently, the easier it is for pearlite to form.

11.33 The three factors that influence the degree to which martensite is formed are as follows:
1) Alloying elements; adding alloying elements increases the extent to which martensite forms.
2) Specimen size and shape; the extent of martensite formation increases as the specimen
cross-section decreases and as the degree of shape irregularity increases.
3) Quenching medium; the more severe the quench, the more martensite is formed. Water
provides a more severe quench than does oil, which is followed by air. Agitating the medium also
enhances the severity of quench.

11.34 The two thermal properties of a liquid medium that influence its quenching effectiveness are
thermal conductivity and heat capacity.

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11.35 (a) This part of the problem calls for us to construct a radial hardness profile for a 50 mm (2 in.)
diameter cylindrical specimen of an 8640 steel that has been quenched in moderately agitated oil. In
the manner of Example Problem 11.1, the equivalent distances and hardnesses tabulated below
were determined from Figures 11.13 and 11.16(b).

Radial Equivalent HRC

Position Distance, mm (in.) Hardness
Surface 7 (5/16) 54
3/4 R 11 (7/16) 50
Midradius 14 (9/16) 45
Center 16 (10/16) 44

The resulting profile is plotted here.

(b) The radial hardness profile for a 75 mm (3 in.) diameter specimen of a 5140 steel that has been
quenched in moderately agitated oil is desired. The equivalent distances and hardnesses for the
various radial positions, as determined using Figures 11.13 and 11.16(b), are tabulated below.

Radial Equivalent HRC

Position Distance, mm (in.) Hardness
Surface 13 (1/2) 41
3/4 R 19 (3/4) 35
Midradius 22 (14/16) 33
Center 25 (1) 31

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 The resulting profile is plotted here.

(c) The radial hardness profile for a 90 mm (3-1/2 in.) diameter specimen of an 8630 steel that has
been quenched in moderately agitated water is desired. The equivalent distances and hardnesses
for the various radial positions, as determined using Figures 11.14 and 11.16(a) are tabulated below.

Radial Equivalent HRC

Position Distance, in. (mm) Hardness
Surface 3 (1/8) 50
3/4 R 10 (3/8) 38
Midradius 17 (11/16) 30
Center 20 (13/16) 28

The resulting profile is plotted here.

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 (d) The radial hardness profile for a 100 mm (4 in.) diameter specimen of a 8660 steel that has been
quenched in moderately agitated water is desired. The equivalent distances and hardnesses for the
various radial positions, as determined using Figures 11.14 and 11.16(a), are tabulated below.

Radial Equivalent HRC

Position Distance, in. (mm) Hardness
Surface 3 (1/8) 63
3/4 R 11 (7/16) 61
Midradius 20 (13/16) 57
Center 27 (1-1/16) 53

The resulting profile is plotted here.

11.36 We are asked to compare the effectiveness of quenching in moderately agitated water and oil by
graphing, on a single plot, the hardness profiles for 75 mm (3 in.) diameter cylindrical specimens of
an 8640 steel that had been quenched in both media.
For moderately agitated water, the equivalent distances and hardnesses for the several
radial positions [Figures 11.16(a) and 11.13] are tabulated below.

Radial Equivalent HRC

Position Distance, mm Hardness
Surface 3 56
3/4 R 9 53
Midradius 13.5 47
Center 16.5 43

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 While for moderately agitated oil, the equivalent distances and hardnesses for the several radial
positions [Figures 11.16(b) and 11.13] are tabulated below.

Radial Equivalent HRC

Position Distance, mm Hardness
Surface 13 48
3/4 R 19 41
Midradius 22 38
Center 25 37

These data are plotted here.

11.37 This problem asks us to compare various aspects of precipitation hardening, and the quenching
and tempering of steel.
(a) With regard to the total heat treatment procedure, the steps for the hardening of steel are as
follows:
1) Austenitize above the upper critical temperature.
2) Quench to a relatively low temperature.
3) Temper at a temperature below the eutectoid.
4) Cool to room temperature.
With regard to precipitation hardening, the steps are as follows:
1) Solution heat treat by heating into the solid solution phase region.
2) Quench to a relatively low temperature.
3) Precipitation harden by heating to a temperature that is within the solid two-phase region.

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