Transcript Chapter 11: Applications & Process. of Metal Alloys

Chapter 11: Applications and
Processing of Metal Alloys
ISSUES TO ADDRESS...
• How are metal alloys classified and what are their
common applications?
• What are some of the common fabrication techniques
for metals?
• What heat treatment procedures are used to improve the
mechanical properties of both ferrous and nonferrous alloys?
Chapter 11 - 1
Classification of Metal Alloys
Metal Alloys
Ferrous
Steels
Steels
<1.4wt%C
<1.4
wt% C
Nonferrous
Cast Irons
Cast
Irons
3-4.5
wt%C
3-4.5 wt% C
microstructure: ferrite,
graphite/cementite
T(ºC)
1600
d
L
1400
1200
g
austenite
g+L
a800
ferrite
600
0
(Fe)
L+Fe3C
1148ºC
4.30
1000
400
Adapted from Fig.
11.1, Callister &
Rethwisch 8e.
727ºC
Eutectoid:
0.76
1
2
Eutectic:
g+Fe3C
Fe3C
cementite
a+Fe3C
3
4
Adapted from Fig. 9.24, Callister &
Rethwisch 8e. (Fig. 9.24 adapted from
Binary Alloy Phase Diagrams, 2nd ed.,
Vol. 1, T.B. Massalski (Ed.-in-Chief),
ASM International, Materials Park, OH,
1990.)
5
6
Co , wt% C
6.7
Chapter 11 - 2
Steels
High Alloy
Low Alloy
low carbon Med carbon
<0.25 wt% C 0.25-0.6wt% C
high carbon
0.6-1.4wt% C
heat
plain
treatable
Cr,V
Cr, Ni
Additions none
none
none
Ni, Mo
Mo
Example 1010 4310
1040
4340 1095
Hardenability 0
+
+
++
++
TS
0
+
++
+
EL
+
+
0
Name
plain
Uses
auto
struc.
sheet
HSLA
bridges
towers
press.
vessels
plain
crank
shafts
bolts
hammers
blades
pistons
gears
wear
applic.
wear
applic.
tool
Cr, V,
Mo, W
4190
+++
++
-drills
saws
dies
increasing strength, cost, decreasing ductility
Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister & Rethwisch 8e.
stainless
Cr, Ni, Mo
304, 409
varies
varies
++
high T
applic.
turbines
furnaces
Very corros.
resistant
Chapter 11 - 3
Refinement of Steel from Ore
Coke
Iron Ore
gas
refractory
vessel
layers of coke
and iron ore
air
slag
Molten iron
Limestone
BLAST FURNACE
heat generation
C+O2 CO2
reduction of iron ore to metal
CO2 + C  2CO
3CO + Fe2O3 2Fe+3CO2
purification
CaCO3  CaO+CO2
CaO + SiO2 + Al2O3  slag
Chapter 11 - 4
Ferrous Alloys
Iron-based alloys
• Steels
• Cast Irons
Nomenclature for steels (AISI/SAE)
10xx Plain Carbon Steels
11xx Plain Carbon Steels (resulfurized for machinability)
15xx Mn (1.00 - 1.65%)
40xx Mo (0.20 ~ 0.30%)
43xx Ni (1.65 - 2.00%), Cr (0.40 - 0.90%), Mo (0.20 - 0.30%)
44xx Mo (0.5%)
where xx is wt% C x 100
example: 1060 steel – plain carbon steel with 0.60 wt% C
Stainless Steel >11% Cr
Chapter 11 - 5
Cast Irons
• Ferrous alloys with > 2.1 wt% C
– more commonly 3 - 4.5 wt% C
• Low melting – relatively easy to cast
• Generally brittle
• Cementite decomposes to ferrite + graphite
Fe3C  3 Fe (a) + C (graphite)
– generally a slow process
Chapter 11 - 6
Fe-C True Equilibrium Diagram
T(ºC)
1600
Graphite formation
promoted by
1400
• Si > 1 wt%
1200
• slow cooling
L
g
Austenite
Liquid +
Graphite
g +L
1153ºC
4.2 wt% C
1000
g + Graphite
a+g
800
0.65
740ºC
600
Adapted from Fig. 11.2,
Callister & Rethwisch 8e.
[Fig. 11.2 adapted from
Binary Alloy Phase
Diagrams, 2nd ed.,
Vol. 1, T.B. Massalski (Ed.in-Chief), ASM International,
Materials Park, OH, 1990.]
400
(Fe)
a + Graphite
0
1
2
3
4
90
C, wt% C
Chapter 11 - 7
100
Types of Cast Iron
Adapted from Fig.
11.3(a) & (b),
Callister &
Rethwisch 8e.
Gray iron
• graphite flakes
• weak & brittle in tension
• stronger in compression
• excellent vibrational dampening
• wear resistant
Ductile iron
• add Mg and/or Ce
• graphite as nodules not flakes
• matrix often pearlite – stronger
but less ductile
Chapter 11 - 8
Types of Cast Iron (cont.)
White iron
• < 1 wt% Si
• pearlite + cementite
• very hard and brittle
Adapted from Fig.
11.3(c) & (d),
Callister &
Rethwisch 8e.
Malleable iron
• heat treat white iron at 800-900ºC
• graphite in rosettes
• reasonably strong and ductile
Chapter 11 - 9
Types of Cast Iron (cont.)
Compacted graphite iron
• relatively high thermal conductivity
• good resistance to thermal shock
• lower oxidation at elevated
temperatures
Adapted from Fig. 11.3(e),
Callister & Rethwisch 8e.
Chapter 11 - 10
Chapter 11 - 11
Chapter 11 - 12
Chapter 11 - 13
Production of Cast Irons
Adapted from Fig.11.5,
Callister & Rethwisch 8e.
Chapter 11 - 14
Limitations of Ferrous Alloys
1) Relatively high densities
2) Relatively low electrical conductivities
3) Generally poor corrosion resistance
Chapter 11 - 15
Nonferrous Alloys
• Cu Alloys
• Al Alloys
-low r: 2.7 g/cm3
Brass: Zn is subst. impurity
(costume jewelry, coins,
-Cu, Mg, Si, Mn, Zn additions
corrosion resistant)
-solid sol. or precip.
Bronze : Sn, Al, Si, Ni are
strengthened (struct.
subst. impurities
aircraft parts
(bushings, landing
& packaging)
gear)
• Mg Alloys
NonFerrous
Cu-Be:
-very low r: 1.7g/cm3
Alloys
precip. hardened
-ignites easily
for strength
-aircraft, missiles
• Ti Alloys
• Refractory metals
-relatively low r: 4.5 g/cm3
-high melting T’s
vs 7.9 for steel
• Noble metals -Nb, Mo, W, Ta
-reactive at high T’s -Ag, Au, Pt
-oxid./corr. resistant
-space applic.
Based on discussion and data provided in Section 11.3, Callister & Rethwisch 3e.
Chapter 11 - 16
Metal Fabrication
• How do we fabricate metals?
– Blacksmith - hammer (forged)
– Cast molten metal into mold
• Forming Operations
– Rough stock formed to final shape
Hot working
vs.
• Deformation temperature
high enough for
recrystallization
• Large deformations
Cold working
• Deformation below
recrystallization
temperature
• Strain hardening occurs
• Small deformations
Chapter 11 - 17
Metal Fabrication Methods (i)
FORMING
CASTING
MISCELLANEOUS
• Forging (Hammering; Stamping) • Rolling (Hot or Cold Rolling)
(wrenches, crankshafts)
force
(I-beams, rails, sheet & plate)
roll
die
A o blank
A d often at
elev. T
• Drawing
force
Ao
Ad
roll
• Extrusion
(rods, wire, tubing)
die
Ao
(rods, tubing)
Ao
tensile
force
die
die must be well lubricated & clean
Ad
force
container
ram
billet
Adapted from
Fig. 11.8,
Callister &
Rethwisch 8e.
die holder
Ad
extrusion
die
ductile metals, e.g. Cu,
Al (hot)
Chapter 11 container
18
Metal Fabrication Methods (ii)
FORMING
CASTING
MISCELLANEOUS
• Casting- mold is filled with molten metal
– metal melted in furnace, perhaps alloying
elements added, then cast in a mold
– common and inexpensive
– gives good production of shapes
– weaker products, internal defects
– good option for brittle materials
Chapter 11 - 19
Metal Fabrication Methods (iii)
FORMING
CASTING
MISCELLANEOUS
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• What material will withstand T >1600ºC
and is inexpensive and easy to mold?
• Answer: sand!!!
Sand
Sand
molten metal
• To create mold, pack sand around form
(pattern) of desired shape
Chapter 11 - 20
Metal Fabrication Methods (iv)
FORMING
CASTING
MISCELLANEOUS
• Investment Casting
(low volume, complex shapes
e.g., jewelry, turbine blades)
• Stage I — Mold formed by pouring
plaster of paris around wax pattern.
Plaster allowed to harden.
wax
I
• Stage II — Wax is melted and then
poured from mold—hollow mold
cavity remains.
II
• Stage III — Molten metal is poured
into mold and allowed to solidify.
III
Chapter 11 - 21
Metal Fabrication Methods (v)
FORMING
CASTING
• Die Casting
-- high volume
-- for alloys having low melting
temperatures
MISCELLANEOUS
• Continuous Casting
-- simple shapes
(e.g., rectangular slabs,
cylinders)
molten
solidified
Chapter 11 - 22
Chapter 11 - 23
Chapter 11 - 24
Metal Fabrication Methods (vi)
FORMING
CASTING
• Powder Metallurgy
(metals w/low ductilities)
MISCELLANEOUS
• Welding
(when fabrication of one large
part is impractical)
pressure
filler metal (melted)
base metal (melted)
fused base metal
heat
area
contact
densify
unaffected
piece 1
heat-affected zone
unaffected
Adapted from Fig.
piece 2
11.9, Callister &
• Heat-affected zone:
point contact
at low T
densification
by diffusion at
higher T
(region in which the
microstructure has been
changed).
Rethwisch 8e.
(Fig. 11.9 from Iron
Castings
Handbook, C.F.
Walton and T.J.
Opar (Ed.), 1981.)
Chapter 11 - 25
Thermal Processing of Metals
Annealing: Heat to Tanneal, then cool slowly.
• Stress Relief: Reduce
• Spheroidize (steels):
stresses resulting from:
- plastic deformation
- nonuniform cooling
- phase transform.
Make very soft steels for
good machining. Heat just
below Teutectoid & hold for
15-25 h.
Types of
Annealing
• Process Anneal:
Negate effects of
cold working by
(recovery/
recrystallization)
Based on discussion in Section 11.7, Callister & Rethwisch 8e.
• Full Anneal (steels):
Make soft steels for
good forming. Heat
to get g, then furnace-cool
to obtain coarse pearlite.
• Normalize (steels): Deform
steel with large grains. Then heat
treat to allow recrystallization
and formation of smaller grains.
Chapter 11 - 26
Heat Treatment Temperature-Time Paths
a) Full Annealing
A
b) Quenching
c) Tempering
(Tempered
Martensite)
P
A
B
Fig. 10.25,
Callister &
Rethwisch 8e.
b)
a)
c)
Chapter 11 - 27
Hardenability -- Steels
• Hardenability – measure of the ability to form martensite
• Jominy end quench test used to measure hardenability.
specimen
(heated to g
phase field)
24ºC water
flat ground
Rockwell C
hardness tests
Adapted from Fig. 11.11,
Callister & Rethwisch 8e.
(Fig. 11.11 adapted from
A.G. Guy, Essentials of
Materials Science,
McGraw-Hill Book
Company, New York,
1978.)
Hardness, HRC
• Plot hardness versus distance from the quenched end.
Adapted from Fig. 11.12,
Callister & Rethwisch 8e.
Distance from quenched end
Chapter 11 - 28
Reason Why Hardness Changes with
Distance
Hardness, HRC
• The cooling rate decreases with distance from quenched end.
60
40
20
0
1
2
3
distance from quenched end (in)
T(ºC)
0%
100%
600
Adapted from Fig. 11.13, Callister &
Rethwisch 8e. (Fig. 11.13 adapted from H.
Boyer (Ed.) Atlas of Isothermal
Transformation and Cooling
Transformation Diagrams, American
Society for Metals, 1977, p. 376.)
400
200
M(start)
AM
0 M(finish)
0.1
1
10
100
1000
Time (s)
Chapter 11 - 29
Hardenability vs Alloy Composition
100
10
3
60
Hardness, HRC
• Hardenability curves for
five alloys each with,
C = 0.4 wt% C
100
• "Alloy Steels"
(4140, 4340, 5140, 8640)
-- contain Ni, Cr, Mo
(0.2 to 2 wt%)
-- these elements shift
the "nose" to longer times
(from A to B)
-- martensite is easier
to form
80 %M
4340
50
40
Adapted from Fig. 11.14, Callister &
Rethwisch 8e. (Fig. 11.14 adapted from
figure furnished courtesy Republic Steel
Corporation.)
2 Cooling rate (ºC/s)
4140
8640
20
5140
0 10 20 30 40 50
Distance from quenched end (mm)
800
T(ºC)
TE
600
A
B
400
200
0 -1
10
10
M(start)
M(90%)
103 105 Time (s)
Chapter 11 - 30
Influences of Quenching Medium &
Specimen Geometry
• Effect of quenching medium:
Medium
air
oil
water
Severity of Quench
low
moderate
high
Hardness
low
moderate
high
• Effect of specimen geometry:
When surface area-to-volume ratio increases:
-- cooling rate throughout interior increases
-- hardness throughout interior increases
Position
center
surface
Cooling rate
low
high
Hardness
low
high
Chapter 11 - 31
Precipitation Hardening
• Particles impede dislocation motion.
700
• Ex: Al-Cu system
T(ºC)
• Procedure:
600
a+L
-- Pt A: solution heat treat
(get a solid solution)
-- Pt B: quench to room temp.
(retain a solid solution)
-- Pt C: reheat to nucleate
small q particles within
a phase.
a
500
400
• Other alloys that precipitation
harden: Temp.
• Cu-Be
• Cu-Sn
• Mg-Al
Adapted from Fig.
11.22, Callister &
Rethwisch 8e.
Pt A (sol’n heat treat)
q+L
A
q
a+q
C
300
0 B 10
(Al)
CuAl2
L
20
30
40
50
wt% Cu
composition range
available for precipitation hardening
Adapted from Fig. 11.24, Callister & Rethwisch 8e.
(Fig. 11.24 adapted from J.L. Murray, International
Metals Review 30, p.5, 1985.)
Pt C (precipitate q)
Pt B
Time
Chapter 11 - 32
Influence of Precipitation Heat
Treatment on TS, %EL
• 2014 Al Alloy:
400
300
200
100
149ºC
204ºC
1min
1h 1day 1mo 1yr
precipitation heat treat time
• Minima on %EL curves.
%EL (2 in sample)
tensile strength (MPa)
• Maxima on TS curves.
• Increasing T accelerates
process.
30
20
10
204ºC
0
149ºC
1min
1h 1day 1mo 1yr
precipitation heat treat time
Adapted from Fig. 11.27, Callister & Rethwisch 8e. (Fig. 11.27 adapted from Metals Handbook:
Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing
Ed.), American Society for Metals, 1979. p. 41.)
Chapter 11 - 33
Summary
• Ferrous alloys: steels and cast irons
• Non-ferrous alloys:
-- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals.
• Metal fabrication techniques:
-- forming, casting, miscellaneous.
• Hardenability of metals
-- measure of ability of a steel to be heat treated.
-- increases with alloy content.
• Precipitation hardening
--hardening, strengthening due to formation of
precipitate particles.
--Al, Mg alloys precipitation hardenable.
Chapter 11 - 34
ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems:
Chapter 11 - 35