Freezing begins ends Temperature & Density for Castings B · Manufacturing Processes for Engineering Materials, ... Temperature & Density for Castings ... Manufacturing Processes

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian • Schmid© 2008, Pearson EducationISBN No. 0-13-227271-7

Temperature & Density for Castings


FIGURE 5.1 (a) Temperature as a function of time for the solidification of pure metals. Note that freezing takes place at a constant temperature. (b) Density as a function of time.

Tem

pera

ture

Time

Cooling of liquid

Cooling ofsolid

BA

LiquidLiquid

+solid

Solid

Freezing begins

Freezingends

Freezingtemperature

Specific

density

Time

Shrinkage of liquid

Shrinkage of solid

Solidificationshrinkage

(a) (b)


Two-Phased Alloys

FIGURE 5.2 (a) Schematic illustration of grains, grain boundaries, and particles dispersed throughout the structure of a two-phase system, such as lead-copper alloy. The grains represent lead in solid solution of copper, and the particles are lead as a second phase. (b) Schematic illustration of a two-phase system, consisting of two sets of grains: dark and light. Dark and light grains have their own compositions and properties.

(b)(a)


Phase Diagram for Nickel-Copper

FIGURE 5.3 Phase diagram for nickel-copper alloy system obtained by a low rate of solidification. Note that pure nickel and pure copper each have one freezing or melting temperature. The top circle on the right depicts the nucleation of crystals; the second circle shows the formation of dendrites; and the bottom circle shows the solidified alloy with grain boundaries.

Solid(42% Cu-58% Ni)

Liquid(50% Cu-50% Ni)

First solid(36% Cu-64% Ni)

Liquid(58% Cu-42% Ni)

0 36 42 50 58 67 100

Solidsolution

Alloy composition

Liquid solution

Fraction liquid

0 1

Solidus

LiquidusL + S

Solid solution(50% Cu-50% Ni)

1981

CS CO CL

1082 1980

2280

23502395

26511455

1249

12881313

Te

mp

era

ture

(°F

)

°C

Composition (% by weight)

Copper (Cu)

100 64 58 50 42 33 0 Nickel (Ni)


Irn-Iron Carbide Phase Diagram

FIGURE 5.4 (a) The iron-iron carbide phase diagram. (b) Detailed view of the microstructures above and below the eutectoid temperature of 727°C (1341°F). Because of the importance of steel as an engineering material, this diagram is one of the most important phase diagrams.

400

500

600

700

800

900

1000

1100

0 0.5 1.0 1.5 2.0 2.5

1000

1500

2000

727°C °F

Te

mp

era

ture

(°C

)

Carbon (% by weight)

! + Fe3C

"

" + Fe3C

Fe3C

Ferrite

!!

! !

!

" + !

Te

mp

era

ture

(°C

)

Carbon (% by weight)

1000

1200

1400

800

600

400

1600

0 1 2 3 4 5 6 6.67

1000

1500

2500

2000

Cementite (Fe3C)

Liquid

727°C

1495°C1538°C

1394°C

912°C °F

0.77%0.022%

4.30%2.11%

1148°C

" (ferrite)

" + cementite

! + cementite

! + liquid

# (Ferrite)

Detail view

(a) (b)

! (austenite)

"+!


Texture in Castings

FIGURE 5.5 Schematic illustration of three cast structures of metals solidified in a square mold: (a) pure metals, with preferred texture at the cool mold wall. Note in the middle of the figure that only favorable oriented grains grow away from the mold surface; (b) solid-solution alloys; and (c) structure obtained by heterogeneous nucleation of grains.

(a)

Chill zone

Equiaxed structureEquiaxed zone

(b) (c)

Columnar zone


Alloy Solidification & Temperature

FIGURE 5.6 Schematic illustration of alloy solidification and temperature distribution in the solidifying metal. Note the formation of dendrites in the semi-solid (mushy) zone.

L + STS

TL

Liquid

Solid

Solid

Solid

Mushy zone

Dendrites

Moldwall

Liquid

Liquid

Te

mp

era

ture

Alloying element (%)

S

L

Liquidus

Solidus

Pure metal


Solidification Patterns for Gray Cast Iron

FIGURE 5.7 Schematic illustration of three basic types of cast structures: (a) columnar dendritic; (b) equiaxed dendritic; and (c) equiaxed nondendritic. Source: After D. Apelian.

(a)

(b)

0.05–0.10% CSteel

0.25–0.30% CSteel

Minutes after pouring

Minutes after pouring

0.55–0.60% CSteel

8 11 40 60 90 102

5 2 15 2 16 2

Sandmold

Chillmold

Sandmold

Chillmold

Sandmold

Chillmold


Cast Structures

FIGURE 5.9 Schematic illustration of cast structures in (a) plane front, single phase, and (b) plane front, two phase. Source: After D. Apelian.

(a) (b) (c)

SolidSolidSolid Liquid Liquid LiquidMoldwall

(a)

Solid LiquidMoldwall Liquid

(b)

FIGURE 5.8 Schematic illustration of three basic types of cast structures: (a) columnar dendritic; (b) equiaxed dendritic; and (c) equiaxed nondendritic. Source: After D. Apelian.


Mold Features

FIGURE 5.10 Schematic illustration of a typical sand mold showing various features.

Open riser

Vent

Pouring basin (cup)

Drag

Cope

Sand

Sprue

Sand

Flask

PartinglineMold

cavity WellGate

Core(sand)

Blindriser

Runner


Temperature Distribution

FIGURE 5.11 Temperature distribution at the mold wall and liquid-metal interface during solidification of metals in casting.

Roomtemperature

Distance

at mold–airinterface

at metal–moldinterface

Meltingpoint

Te

mp

era

ture

Air Solid Liquid

!T

!T

Mold


Skin on Casting

FIGURE 5.12 Solidified skin on a steel casting; the remaining molten metal is poured out at the times indicated in the figure. Hollow ornamental and decorative objects are made by a process called slush casting, which is based on this principle. Source: After H.F. Taylor, J. Wulff, and M.C. Flemings.

5 s 1 min 2 min 6 min

A

B

Chvorinov’s Rule:

Solidification time=C!

VolumeSurface area

"n


Shrinkage

Contraction (%) Expansion (%)Aluminum 7.1 Bismuth 3.3Zinc 6.5 Silicon 2.9Al - 4.5% Cu 6.3 Gray iron 2.5Gold 5.5White iron 4-5.5Copper 4.9Brass (70-30) 4.5Magnesium 4.290% Cu - 10% Al 4Carbon steels 2.5-4Al - 12% Si 3.8Lead 3.2

TABLE 5.1 Volumetric solidification contraction or expansion for various cast metals.


Cast Material Properties

FIGURE 5.13 Mechanical properties for various groups of cast alloys. Compare with various tables of properties in Chapter 3. Source: Courtesy of Steel Founders' Society of America.

Ste

el

Nodula

r iron

Gra

y iro

n

Malle

able

iro

n

Alu

min

um

based

Copper

based

Magnesiu

m b

ased

Nic

kel based

Zin

c b

ased

Ultim

ate

tensile

str

ength

(psi x 1

03)

300

280

260

240

220

200

180

160

140

120

100

80

60

40

20

0

2000

1800

2000

1800

1600

1400

1200

1000

800

600

400

200

MP

a

(a)

300

280

260

240

220

200

180

160

140

120

100

80

60

40

20

0

1600

1400

1200

1000

800

600

400

200

Ste

el

Nodula

r iron

Gra

y iro

n

Malle

able

iro

n

Alu

min

um

based

Copper

based

Magnesiu

m b

ased

Nic

kel based

Zin

c b

ased

Yie

ld s

trength

(psi x 1

03)

MP

a

(b)

Nodula

r iron

Gra

y iro

n Malle

able

iron

Alu

min

um

based

Copper

based

Magnesiu

m b

ased

Nic

kel based

Zin

c b

ased

Titaniu

m m

eta

l

Titaniu

m a

lloys

Cast ste

el

0

5

10

20

25

30

15

0

50

100

200

150

GP

a

Modulu

s o

f ela

sticity (

psi x 1

06)

0

10

12

8

6

4

2

Wrought

Cast

Ste

el

Nodula

r iron

Gra

y iro

n

Malle

able

iro

n

Alu

min

um

based

Magnesiu

m b

ased

Titaniu

m m

eta

l Titaniu

mallo

y

Tensile

str

ength

/density r

atio (

in x

10

5)

(d)(c)

Nodula

r iron

Gra

y iro

n

Alu

min

um

based

Copper

based

Magnesiu

m b

ased

Nic

kel based

Zin

c b

ased

Ste

el

Malle

able

iro

n

800

700

600

500

400

300

200

100

0

Brinell

harb

ness (

HB

)

(e)

Malle

able

iro

n

70

60

50

40

30

20

10

0

90

80

70

60

50

40

30

20

10

0

Ste

el

Nodula

r iron

Gra

y iro

n

J

Impact energ

y (

ft-lb, C

harp

y V

-notc

h)

(f)

70

60

50

40

30

20

10

0

Nodula

r iron

Malle

able

iro

n

Copper

based

Nic

kel based

Ste

el

Gra

y iro

n

Copper

based

Nic

kel based

Reduction o

f are

a (

%)

(h)

Nodula

r iron

Gra

y iro

n

Alu

min

um

based C

opper

based

Magnesiu

m b

ased N

ickel based

Zin

c b

ased

Ste

el

Malle

able

iro

n

70

60

50

40

30

20

10

0

Elo

ngation (

%)

(g)


General Characteristics of Casting

TABLE 5.2 General characteristics of casting processes.

Evaporative PermanentSand Shell pattern Plaster Investment mold Die Centrifugal

Typical materials cast All All All Nonferrous All All Nonferrous All(Al, Mg, (Al, Mg,Zn, Cu) Zn, Cu)

Weight (kg):minimum 0.01 0.01 0.01 0.01 0.001 0.1 < 0.01 0.01maximum No limit 100+ 100+ 50+ 100+ 300 50 5000+

Typ. surface finish (µm Ra) 5-25 1-3 5-25 1-2 0.3-2 2-6 1-2 2-10Porosity1 3-5 4-5 3-5 4-5 5 2-3 1-3 1-2Shape complexity1 1-2 2-3 1-2 1-2 1 2-3 3-4 3-4Dimensional accuracy1 3 2 3 2 1 1 1 3Section thickness (mm):

minimum: 3 2 2 1 1 2 0.5 2maximum: No limit — — — 75 50 12 100

Typ. dimensional tolerance 1.6-4 ±0.003 ±0.005! ±0.005 ±0.015 ±0.001! ±0.015(0.25 for 0.010 0.005small)

Cost1,2

Equipment 3-5 3 2-3 3-5 3-5 2 1 1Pattern/die 3-5 2-3 2-3 3-5 2-3 2 1 1Labor 1-3 3 3 1-2 1-2 3 5 5

Typical lead time2,3 Days Weeks weeks Days Weeks Weeks Weeks- Monthsmonths

Typical production rate2,3 1-20 5-50 1-20 1-10 1-1000 5-50 2-200 1-1000Minimum quantity2,3 1 100 500 10 10 1000 10,000 10-10,000Notes:1. Relative rating, 1 best, 5 worst. For example, die casting has relatively low porosity, mid- to low shape complexity, high dimensionalaccuracy, high equipment and die costs and low labor costs. These ratings are only general; significant variations can occur dependingon the manufacturing methods used.2. Data taken from Schey, J.A., Introduction to Manufacturing Processes, 3rd ed, 2000.3. Approximate values without the use of rapid prototyping technologies.


Typical Applications & Characteristics

TABLE 5.3 Typical applications for castings and casting characteristics.

Type of Alloy Application Castability! Weldability! Machinability!Aluminum Pistons, clutch housings, intake mani-

folds, engine blocks, heads, cross mem-bers, valve bodies, oil pans, suspensioncomponents

G-E F* G-E

Copper Pumps, valves, gear blanks, marine pro-pellers

F-G F G-E

Gray Iron Engine blocks, gears, brake disks anddrums, machine bases

E D G

Magnesium Crankcase, transmission housings,portable computer housings, toys

G-E G E

Malleable iron Farm and construction machinery, heavy-duty bearings, railroad rolling stock

G D G

Nickel Gas turbine blades, pump and valve com-ponents for chemical plants

F F F

Nodular iron Crankshafts, heavy-duty gears G D GSteel (carbonand low alloy)

Die blocks, heavy-duty gear blanks, air-craft undercarriage members, railroadwheels

F E F-G

Steel (high al-loy)

Gas turbine housings, pump and valvecomponents, rock crusher jaws

F E F

White iron(Fe3C)

Mill liners, shot blasting nozzles, railroadbrake shoes, crushers and pulverizers

G VP VP

Zinc Door handles, radiator grills E D E! E, excellent; G, good; F, fair; VP, very poor; D, di!cult.


Properties & Applications of Cast Iron

TABLE 5.4 Properties and typical applications of cast irons.

UltimateTensile Yield Elonga-

Cast Strength Strength tion inIron Type (MPa) (MPa) 50 mm (%) Typical ApplicationsGray Ferritic 170 140 0.4 Pipe, sanitary ware

Pearlitic 275 240 0.4 Engine blocks, machine toolsMartensitic 550 550 0 Wear surfaces

Ductile Ferritic 415 275 18 Pipe, general service(Nodular) Pearlitic 550 380 6 Crankshafts, highly stressed parts

Tempered 825 620 2 High-strength machine parts, wearMartensite resistance

Malleable Ferritic 365 240 18 Hardware, pipe fittings, generalengineering service

Pearlitic 450 310 10 CouplingsTempered 700 550 2 Gears, connecting rods

White Pearlitic 275 275 0 Wear resistance, mill rolls


Nonferrous Alloys

TABLE 5.5 Typical properties of nonferrous casting alloys.

Casting UTS Yield Strength Elongation HardnessAlloy Condition Method! (MPa) (MPa) in 50 mm (%) (HB)Aluminum

357 T6 S 345 296 2.0 90380 F D 331 165 3.0 80390 F D 279 241 1.0 120

MagnesiumAZ63A T4 S, P 275 95 12 —AZ91A F D 230 150 3 —QE22A T6 S 275 205 4 —

CopperBrass C83600 — S 255 177 30 60Bronze C86500 — S 490 193 30 98Bronze C93700 — P 240 124 20 60

ZincNo. 3 — D 283 — 10 82No. 5 — D 331 — 7 91ZA27 — P 425 365 1 115

! S, sand; D, die; P, permanent mold.


Microstructure for Cast Irons

FIGURE 5.14 Microstructure for cast irons. (a) ferritic gray iron with graphite flakes; (b) ferritic nodular iron, (ductile iron) with graphite in nodular form; and (c) ferritic malleable iron. This cast iron solidified as white cast iron, with the carbon present as cementite (Fe3C), and was heat treated to graphitize the carbon.

(a) (b) (c)


Continuous-Casting

FIGURE 5.15 (a) The continuous-casting process for steel. Note that the platform is about 20 m (65 ft) above ground level. Source: American Foundrymen's Society. (b) Continuous strip casting of nonferrous metal strip. Source: Courtesy of Hazelett Strip-Casting Corp.

Electric furnace

Tundish

Argon

X-ray receiver(controls pouring rate)

X-ray transmitter

Molten metal

Solidified metal

Oil

Cooling water

Platform; 20 m (701 ft)above ground level

Air gap

Catch basin

Pinch rolls

Oxygen lance(for cutting)

Starting dummy

Tundish

Top belt (carbon steel)

High-velocitycooling water jetsBack-up rolls

Bottombelt Water gutters

Nip pulley Synchronizedpinch rolls

Tensionpulley

Edge dam blocks

Water nozzle

(a) (b)


Sand Casting

FIGURE 5.16 Schematic illustration of the sequence of operations in sand casting. (a) A mechanical drawing of the part, used to create patterns. (b-c) Patterns mounted on plates equipped with pins for alignment. Note the presence of core prints designed to hold the core in place. (d-e) Core boxes produce core halves, which are pasted together. The cores will be used to produce the hollow area of the part shown in (a). (f) The cope half of the mold is assembled by securing the cope pattern plate to the flask with aligning pins, and attaching inserts to form the sprue and risers. (g) The flask is rammed with sand and the plate and inserts are removed. (h) The drag half is produced in a similar manner. (j) The core is set in place within the drag cavity. (k) The mold is closed by placing the cope on top of the drag and securing the assembly with pins. (l) After the metal solidifies, the casting is removed from the mold. (m) The sprue and risers are cut off and recycled, and the casting is cleaned, inspected, and heat treated (when necessary). Source: Courtesy of Steel Founders' Society of America.

Cope ready for sand

Cope after rammingwith sand and

removing pattern,sprue, and risers

Drag readyfor sand

Drag afterremoving pattern

Core halvespasted together

(e) (f) (g) (h) (i)

Sprue

Risers

Flask

Drag with coreset in place

(j)

Cope and drag assembledand ready for pouring

(k)

Cope

Drag

Closingpins

Casting as removedfrom mold; heat treated

(l)

Casting readyfor shipment

(m)

(a)

Mechanical drawing of part Core boxesCope pattern plate Drag pattern plate

(d)(b) (c)

Core prints Gate

Core prints


Shell-Molding Process

FIGURE 5.17 Schematic illustration of the shell-molding process, also called the dump-box technique.

Pattern

Coatedsand

Dump box

1. Pattern rotatedand clamped to dump box

Shell

Excesscoated sand

4. Pattern and shellremoved from dump box

Coatedsand

3. Pattern and dump boxin position for the investment

Investment

Pattern

Coated sand

2. Pattern and dumpbox rotated

Adhesive Clamps

5. Mold halves joined together

Flask

Sand ormetal beads

Shells

6. Mold placed in flaskand metal poured


Caramic Mold Manufacture

FIGURE 5.18 Sequence of operations in making a ceramic mold.

3. Burn-off2. Stripping green mold1. Pouring slurry

Flask

Greenmold

Pattern

Plate

Ceramic slurry

Pattern

Transfer bowl

Flask

Torch

Mold


Vacuum-Casting Process

FIGURE 5.19 Schematic illustration of the vacuum-casting process. Note that the mold has a bottom gate. (a) before and (b) after immersion of the mold into the molten metal. Source: After R. Blackburn.

Mold

(a) (b)

Induction furnace

Vacuum

Casting

Molten metal

Gate


Evaporative Pattern Casting

FIGURE 5.20 Schematic illustration of the expendable-pattern casting process, also known as lost-foam or evaporative-pattern casting.

1. Pattern molding

4. Compacted in sand 5. Casting

6. Shakeout

2. Cluster assembly3. Coating

Cluster

Parts


Investment Casting

FIGURE 5.21 Schematic illustration of investment casting (lost wax process). Castings by this method can be made with very fine detail and from a variety of metals. Source: Steel Founders' Society of America.

9. Shakeout8. Pouring7. Pattern meltout6. Completed mold

Casting

10. Pattern

Moltenmetal

Autoclaved

Molten waxor plastic

Heat Heat

1. Injection wax orplastic pattern

4. Slurry coating2. Ejectingpattern

5. Stucco coating3. Patternassembly (tree)

Waxpattern

Mold to make pattern


Rotor Microstructure

FIGURE 5.22 Microstructure of a rotor that has been investment cast (top) and conventionally cast (bottom). Source: Advanced Materials and Processes, October 1990, p. 25. ASM International.


Pressure & Hot-Chamber Die Casting

FIGURE 5.23 The pressure casting process, utilizing graphite molds for the production of steel railroad wheels. Source: Griffin Wheel Division of Amsted Industries Incorporated.

Airtightchamber

Ladle Refractory tube

Molten metal

Air pressure

Railroad wheelGraphite mold

FIGURE 5.24 Schematic illustration of the hot-chamber die-casting process.

Gooseneck

Nozzle

Die cavity

Hydraulic shotcylinder

Plunger rod

Plunger

Molten metal

Pot

Ejector die

Cover die

Furnace


Cold-Chamber Die Casting

FIGURE 5.25 Schematic illustration of the cold-chamber die-casting process. These machines are large compared to the size of the casting, because high forces are required to keep the two halves of the die closed under pressure.

Shotcylinder

Metalsleeve

Coverdisc

Closingcylinder

Ejectorbox

Ejector platen(Moves)

Ejectordie half

Hydrauliccylinder

Shotsleeve

Ejector box

Ladle

Stationarydie half

Plungerrod

Stationary platenCavity

Pouring hole

Plunger

Plunger rod


Properties of Die-Casting AlloysUltimate Elonga-Tensile Yield tion

Strength Strength in 50 mmAlloy (MPa) (MPa) (%) ApplicationsAluminum 380 320 160 2.5 Appliances, automotive

(3.5 Cu-8.5 Si) components, electrical motorframes and housings, engineblocks.

Aluminum 13 300 150 2.5 Complex shapes with thin(12 Si) walls, parts requiring strength at

elevated temperaturesBrass 858 (60 Cu) 380 200 15 Plumbing fixtures, lock hard-

ware, bushings, ornamental cast-ings

Magnesium 230 160 3 Power tools, automotiveAZ91B (9 Al - 0.7 Zn) parts, sporting goods

Zinc No. 3 (4 Al) 280 — 10 Automotive parts, o!ce equip-ment, household utensils, build-ing hardware, toys

Zinc No. 5 (4 Al - 1 Cu) 320 — 7 Appliances, automotive parts,building hardware, businessequipment

Source: The North American Die Casting Association

TABLE 5.6 Properties and typical applications of common die-casting alloys.


Centrifugal Casting

FIGURE 5.26 Schematic illustration of the centrifugal casting process. Pipes, cylinder liners, and similarly shaped hollow parts can be cast by this process.

Free rollerDrive roller

Mold

(a) (b)

Drive shaft

Spout

Rollers

Ladle

Molten metalMold


Semicentrifugal Casting

FIGURE 5.27 (a) Schematic illustration of the semicentrifugal casting process. Wheels with spokes can be cast by this process. (b) Schematic illustration of casting by centrifuging. The molds are placed at the periphery of the machine, and the molten metal is forced into the molds by centrifugal forces.

(a) (b)

Mold

Molten metal

CastingFlasks

Holdingfixture

Drag

Revolvingtable

CastingPouring basinand gate

Cope


Squeeze-Casting

FIGURE 5.28 Sequence of operations in the squeeze-casting process. This process combines the advantages of casting and forging.

1. Melt metal 2. Pour molten

metal into die

3. Close die and

apply pressure

4. Eject squeeze casting,

charge melt stock,

repeat cycle

Die

Ejector

pin

Finished

casting

Cavity


Turbine Blade Casting

FIGURE 5.29 Methods of casting turbine blades: (a) directional solidification; (b) method to produce a single-crystal blade; and (c) a single-crystal blade with the constriction portion still attached. Source: (a) and (b) After B.H. Kear, (c) Courtesy of ASM International.

(c)(a) (b)

Radiantheat

Columnarcrystals

Constriction

Chill plate

Columnarcrystals

Heatbaffles

Radiantheat

Chill plate


Crystal Growing

FIGURE 5.30 Two methods of crystal growing: (a) crystal pulling (Czochralski process) and (b) floating-zone method. Crystal growing is especially important in the semiconductor industry. (c) A single-crystal silicon ingot produced by the Czochralski process. Source: Courtesy of Intel Corp.

(c)(a) (b)

~1 rev/s

10 µ

m/s

Liquid

Seed

20 µ

m/s

Inductioncoil

Sin

gle

cry

sta

lP

oly

cry

sta

lline

feed


Melt-Spinning Process

FIGURE 5.31 (a) Schematic illustration of the melt-spinning process to produce thin strips of amorphous metal. (b) Photograph of nickel-alloy production through melt-spinning. Source: Courtesy of Siemens AG.

(b)(a)

Crucible

Induction coil

Melt

Strip

Gas

Copper disk


Austenite-Pearlite Transformation

FIGURE 5.32 (a) Austenite to pearlite transformation of iron-carbon alloys as a function of time and temperature. (b) Isothermal transformation diagram obtained from (a) for a transformation temperature of 675°C (1247°F). (c) Microstructures obtained for a eutectoid iron-carbon alloy as a function of cooling rate. Source: Courtest of ASM International.

(a)

25

75

50

0

100

75

25

50

100

0

Au

ste

nite

(%

)

Pe

arlite

(%

)

Time (s)

600°C 650° 675°

1 10 102 103

(b) (c)

50

0

100

Pe

rce

nt

of

au

ste

nite

tr

an

sfo

rme

d t

o p

ea

rlite

Te

mp

era

ture

(° C

)

Au

ste

nite

(%

) ° F

50

100

0

600

400

500

700

800

1000

1200

1400

Time (s)

50% Completion curve

Pearlite

Completion curve (~100% pearlite)

Eutectoid temperature

Austenite (unstable)

Begin curve (~0% pearlite)

Transformationtemperature675°C

Transformation begins

1 10 103 104 105

Transformation ends

1 10 102 103 104 105

Austenite (stable)

102

Time (s)

Te

mp

era

ture

(° C

)

200

100

0

200

400

600

800

1000

1200

1400

300

400

500

35°C

/s

140 °C

/s

600

700

800

Eutectoid temperature

M (start)

Critical cooling

rate

Time (s)

1 10 102 10-1 103 104 105

°F

Pearlite Martensite

Martensite+ pearlite

Austenite pearlite


Phase Diagram for Aluminum-Copper

FIGURE 5.33 (a) Phase diagram for the aluminum-copper alloy system. (b) Various microstructures obtained during the age-hardening process.

X

Te

mp

era

ture

X—solid solution

XA—quenched, solid solution retained

AB—age-hardened, precipitation starts

(submicroscopic)

AC—over-aging, precipitate agglomerates

100 95 90 Aluminum (Al)

0 5 10 Copper (Cu)

70

400

900

1100

Liquid

+ liquid

20

200

500

600

700

(b) (a)

1300

Composition (% by weight)

Te

mp

era

ture

(°C

)

°F

A B C

Time

+ !


Outline of Heat Treating

TABLE 5.7 Outline of heat treatment processes for surface hardening.

ElementMetals added to General Typical

Process hardened surface Procedure characteristics applicationsCarburizing Low-carbon

steel (0.2%C), alloy steels(0.08-0.2% C)

C Heat steel at 870-950!(1600-1750!F) in an at-mosphere of carboaceousgases (gas carburizing) orcarbon-containing solids(pack carburizing). Thenquench.

A hard, high-carbon surfaceis produced. Hardness 55-65 HRC. Case depth <0.5-1.5 mm (<0.020 to 0.060 in.).Some distortion of part dur-ing heat treatment.

Gears, cams,shafts, bearings,piston pins,sprockets, clutchplates

Carbonitriding Low-carbonsteel

C and N Heat steel at 700-800!C(1300-1600!F) in an atmo-sphere of carbonaceous gasand ammonia. Then quenchin oil.

Surface hardness 55-62 HRC.Case depth 0.07-0.5 mm(0.003-0.020 in.). Less distor-tion than in carburizing.

Bolts, nuts,gears.

Cyaniding Low-carbonsteel (0.2%C), alloy steels(0.08-0.2% C)

C and N Heat steel at 760-845!C(1400-1550!F) in a moltenbath of solutions of cyanide(e.g., 30% sodium cyanide)and other salts.

Surface hardness up to 65HRC. Case depth 0.025-0.25mm (0.001-0.010 in.). Somedistortion.

Bolts, nuts,screws, smallgears.

Nitriding Steels (1% Al,1.5% Cr, 0.3%Mo), alloy steels(Cr, Mo), stain-less steels, high-speed steels

N Heat steel at 500-600!C (925-1100!F) in an atmosphere ofammonia gas or mixtures ofmolten cyanide salts. No fur-ther treatment.

Surface hardness up to 1100HV. Case depth 0.1-0.6 mm(0.005-0.030 in.) and 0.02-0.07 mm (0.001-0.003 in.) forhigh speed steel.

Geards, shafts,sprockets,valves, cutters,boring bars

Boronizing Steels B Part is heated using boron-containing gas or solid in con-tact with part.

Extremely hard and wear-resistance surface. Casedepth 0.025-0.075 mm(0.001-0.003 in.).

Tool and diesteels.

Flamehardening

Medium-carbonsteels, cast irons

None Surface is heated with anoxyacetylene torch, thenquenched with water sprayor other quenching methods.

Surface hardness 50-60 HRC.Case depth 0.7-6 mm (0.030-0.25 in.). Little distortion.

Axles,crankshafts,piston rods,lathe beds, andcenters.

Inductionhardening

Same as above None Metal part is placed in cop-per induction coils and isheated by high frequency cur-rent, then quenched

Same as above Same as above


Heat Treatment Temperature Ranges

FIGURE 5.34 Temperature ranges for heat treating plain-carbon steels, as indicated on the iron-iron carbide phase diagram.

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

Te

mp

era

ture

(°C

)

600

700

800

900

1000

1200

1400

1600

1800

Normalizing

Full annealing

Acm

Spheroidizing

738°C

A3

A1

Composition (% C)

°F


Casting Processes Comparison

TABLE 5.8 Casting Processes, and their Advantages and Limitations.

Process Advantages LimitationsSand Almost any metal is cast; no limit to

size, shape or weight; low tooling cost.Some finishing required; somewhatcoarse finish; wide tolerances.

Shell mold Good dimensional accuracy and sur-face finish; high production rate.

Part size limited; expensive patternsand equipment required.

Expendable pattern Most metals cast with no limit to size;complex shapes

Patterns have low strength and canbe costly for low quantities.

Plaster mold Intricate shapes; good dimensionalaccuracy and finish; low porosity.

Limited to nonferrous metals; limitedsize and volume of production; moldmaking time relatively long.

Ceramic mold Intricate shapes; close toleranceparts; good surface finish.

Limited size.

Investment Intricate shapes; excellent surface fin-ish and accuracy; almost any metalcast.

Part size limited; expensive patterns,molds, and labor.

Permanent mold Good surface finish and dimensionalaccuracy; low porosity; high produc-tion rate.

High mold cost; limited shape and in-tricacy; not suitable for high-melting-point metals.

Die Excellent dimensional accuracy andsurface finish; high production rate.

Die cost is high; part size limited; usu-ally limited to nonferrous metals; longlead time.

Centrifugal Large cylindrical parts with goodquality; high production rate.

Equipment is expensive; part shapelimited.


Chills

FIGURE 5.35 Various types of (a) internal and (b) external chills (dark areas at corners), used in castings to eliminate porosity caused by shrinkage. Chills are placed in regions where there is a larger volume of metal, as shown in (c).

(a)

(b)

(c)

PorosityChill

Casting

Boss

Chill

Sand

Casting Chill

Sand


Hydrogen Solubility in Aluminum

FIGURE 5.36 Solubility of hydrogen in aluminum. Note the sharp decrease in solubility as the molten metal begins to solidify.

Hydro

gen s

olu

bili

ty

Fusion

Solid

Liquid

Melting point


Elimination of Porosity in Castings

FIGURE 5.37 (a) Suggested design modifications to avoid defects in castings. Note that sharp corners are avoided to reduce stress concentrations; (b, c, d) examples of designs showing the importance of maintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities.

(a)

Poor

Good

(b) (c) (d)

Shrinkagecavity

Poor Poor

Good Good


Design Modifications

FIGURE 5.38 Suggested design modifications to avoid defects in castings. Source: Courtesy of The North American Die Cast ing Association.

Use radii or fillets to avoid cornersand provide uniform cross-section.

Wall sections should be uniform.

Sloping bosses can be designed forstraight die parting to simplify die design.

Ribs and/or fillets improve bosses.

Side cores can be eliminatedwith this hole design.

Deep cavities should be on oneside of the casting where possible.

Poor Good

Poor Good

Poor GoodPoor Good

Poor Good

Poor Good

Core incover half

Core inejector half


Economics of Casting

FIGURE 5.39 Economic comparison of making a part by two different casting processes. Note that because of the high cost of equipment, die casting is economical mainly for large production runs. Source: The North American Die Casting Association.

Co

st

pe

r p

iece

(re

lative

)

8

7

6

5

4

3

2

1

0100 101 102 103 104 105 106

Number of pieces

Die cast

Sand cast

Permanent-moldcasting

Plaster cast


Lost-Foam Casting of Engine Blocks

FIGURE 5.40 (a) An engine block for a 60-hp 3-cylinder marine engine, produced by the lost-foam casting process; (b) a robot pouring molten aluminum into a flask containing a polystyrene pattern. In the pressurized lost-foam process, the flask is then pressurized to 150 psi (1000 kPa). Source: Courtesy of Mercury Marine

(a) (b)

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