Transcript REFINEMENT OF STEEL FROM ORE

CHAPTER 14:
SYNTHESIS, FABRICATION, AND
PROCESSING OF MATERIALS
ISSUES TO ADDRESS...
• What are the common fabrication techniques for metals?
• How do the properties vary throughout a piece of metal that
has been quenched?
• How can properties be modified by a post heat treatment?
• How is the processing of ceramics different than for metals?
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REFINEMENT OF STEEL FROM
ORE
Coke
Limestone
Iron Ore
gas
refractory
vessel
layers of coke
and iron ore
air
slag
Molten iron
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 +Al 2O3slag
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METAL FABRICATION METHODS-I
FORMING
• Forging
(wrenches, crankshafts)
force
die
Ao blank
• Rolling
(I-beams, rails)
Ad often at
elev. T
• Drawing
force
• Extrusion
(rods, wire, tubing)
die
Ao
die
Ad
Adapted from
Fig. 11.7,
Callister 6e.
(rods, tubing)
tensile
force
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FORMING TEMPERATURE
• Hot working
--recrystallization
• Cold working
--recrystallization
--less energy to deform
--oxidation: poor finish
--lower strength
--less energy to deform
--oxidation: poor finish
--lower strength
• Cold worked microstructures
--generally are very anisotropic!
--Forged
(a)
--Swaged
(b)
--Fracture resistant!
(c)
Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering
Materials", (4th ed.), John Wiley and Sons, Inc., 1996. (a) Fig. 10.5, p. 410 (micrograph courtesy of G.
Vander Voort, Car Tech Corp.); (b) Fig. 10.6(b), p. 411 (Orig. source: J.F. Peck and D.A. Thomas,
Trans. Metall. Soc. AIME, 1961, p. 1240); (c) Fig. 10.10, p. 415 (Orig. source: A.J. McEvily, Jr.
and R.H. Bush, Trans. ASM 55, 1962, p. 654.)
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METAL FABRICATION METHODSII
CASTING
• Sand Casting
(large parts, e.g.,
auto engine blocks)
• Investment Casting
• Die Casting
(high volume, low T alloys)
• Continuous Casting
(simple slab shapes)
(low volume, complex shapes
e.g., jewelry, turbine blades)
plaster
die formed
around wax
prototype
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METAL FABRICATION METHODSIII
FORMING
• Powder Processing
(materials w/low ductility)
CASTING
JOINING
• Welding
(when one large part is
impractical)
filler metal (melted)
base metal (melted)
fused base metal
unaffected
piece 1
heat affected zone
unaffected
Adapted from Fig.
piece 2
11.8, Callister 6e.
(Fig. 11.8 from
• Heat affected zone:
Iron Castings
Handbook, C.F.
Walton and T.J.
(region in which the
Opar (Ed.), 1981.)
microstructure has been
changed).
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THERMAL PROCESSING OF
Annealing: Heat to METALS
Tanneal, then cool slowly.
Based on discussion in Section 11.7, Callister 6e.
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HARDENABILITY--STEELS
• Ability to form martensite
• Jominy end quench test to measure hardenability.
1”
specimen
(heated to 
phase field)
24°C water
flat ground
4”
Adapted from Fig. 11.10,
Callister 6e. (Fig. 11.10
adapted from A.G. Guy,
Essentials of Materials
Science, McGraw-Hill
Book Company, New
York, 1978.)
• Hardness versus distance from the quenched end.
Adapted from Fig. 11.11,
Callister 6e.
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WHY HARDNESS CHANGES
W/POSITION
• The cooling rate varies with position.
Adapted from Fig. 11.12, Callister 6e.
(Fig. 11.12 adapted from H. Boyer (Ed.)
Atlas of Isothermal Transformation
and Cooling Transformation Diagrams,
American Society for Metals, 1977, p.
376.)
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HARDENABILITY VS ALLOY CONTENT
• Jominy end quench
results, C = 0.4wt%C
Adapted from Fig. 11.13, Callister 6e.
(Fig. 11.13 adapted from figure
furnished courtesy Republic Steel
Corporation.)
• "Alloy Steels"
(4140, 4340, 5140, 8640)
--contain Ni, Cr, Mo
(0.2 to 2wt%)
--these elements shift
the "nose".
--martensite is easier
to form.
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•
QUENCHING MEDIUM &
GEOMETRY
Effect of quenching medium:
Medium
air
oil
water
Severity of Quench
small
moderate
large
Hardness
small
moderate
large
• Effect of geometry:
When surface-to-volume ratio increases:
--cooling rate increases
--hardness increases
Position Cooling rate
center
small
surface
large
Hardness
small
large
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• Ex:
PREDICTING HARDNESS
PROFILES
Round bar, 1040
steel, water quenched, 2" diam.
Adapted from Fig. 11.18, Callister 6e.
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CERAMIC FABRICATION METHODS-I
GLASS
FORMING
• Pressing:
Gob
• Fiber drawing:
Pressing
operation
Parison
mold
• Blowing:
Adapted from Fig. 13.7, Callister, 6e. (Fig. 13.7 is adapted from C.J. Phillips,
Glass: The Miracle Maker, Pittman Publishing Ltd., London.)
wind up
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GLASS STRUCTURE
• Basic Unit:
4Si0 4 tetrahedron
Si4+
O2-
• Glass is amorphous
• Amorphous structure
occurs by adding impurities
(Na+,Mg2+,Ca2+, Al3+)
• Impurities:
interfere with formation of
crystalline structure.
• Quartz is crystalline
SiO2:
(soda glass)
Adapted from Fig. 12.11,
Callister, 6e.
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GLASS PROPERTIES
• Specific volume (1/r) vs Temperature (T):
• Crystalline materials:
--crystallize at melting temp, Tm
--have abrupt change in spec.
vol. at Tm
• Glasses:
Adapted from Fig. 13.5, Callister, 6e.
• Viscosity:
--relates shear stress &
velocity gradient:
--has units of (Pa-s)
--do not crystallize
--spec. vol. varies smoothly with T
--Glass transition temp, Tg
dv

dy
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GLASS VISCOSITY VS T AND
IMPURITIES
• Viscosity decreases with T
• Impurities lower Tdeform
Adapted from Fig. 13.6, Callister, 6e.
(Fig. 13.6 is from E.B. Shand, Engineering
Glass, Modern Materials, Vol. 6,
Academic Press, New York, 1968, p. 262.)
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HEAT TREATING GLASS
• Annealing:
--removes internal stress caused by uneven cooling.
• Tempering:
--puts surface of glass part into compression
--suppresses growth of cracks from surface scratches.
--sequence:
before cooling
hot
surface cooling
cooler
hot
cooler
further cooled
compression
tension
compression
--Result: surface crack growth is suppressed.
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CERAMIC FABRICATION METHODS-IIA
PARTICULATE
FORMING
• Milling and screening: desired particle size
• Mixing particles & water: produces a "slip"
• Form a "green" component
--Hydroplastic forming:
extrude the slip (e.g., into a pipe)
Adapted from
Fig. 11.7,
Callister 6e.
--Slip casting:
Adapted from Fig.
13.10, Callister 6e.
(Fig. 13.10 is from
W.D. Kingery,
Introduction to
Ceramics, John
solid component
hollow component
• Dry and Fire the component
Wiley and Sons,
Inc., 1960.)
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FEATURES OF A SLIP
• Clay is inexpensive
• Adding water to clay
--allows material to shear easily
along weak van der Waals bonds
--enables extrusion
--enables slip casting
• Structure of
Kaolinite Clay:
Adapted from Fig. 12.14, Callister 6e.
(Fig. 12.14 is adapted from W.E. Hauth,
"Crystal Chemistry of Ceramics",
American Ceramic Society Bulletin, Vol.
30 (4), 1951, p. 140.)
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DRYING AND FIRING
• Drying: layer size and spacing decrease.
Adapted from Fig.
13.11, Callister 6e.
(Fig. 13.11 is from
W.D. Kingery,
Introduction to
Ceramics, John
Wiley and Sons,
Inc., 1960.)
• Firing:
--T raised to (900-1400 C)
--vitrification: glass forms from clay and flows between
SiO2 particles.
Adapted from Fig. 13.12,
Callister 6e.
(Fig. 13.12 is courtesy
H.G. Brinkies, Swinburne
University of Technology,
Hawthorn Campus,
Hawthorn, Victoria,
Australia.)
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CERAMIC FABRICATION METHODS-IIB
PARTICULATE
FORMING
• Sintering: useful for both clay and non-clay compositions.
• Procedure:
--grind to produce ceramic and/or glass particles
--inject into mold
--press at elevated T to reduce pore size.
• Aluminum oxide powder:
--sintered at 1700C
for 6 minutes.
Adapted from Fig. 13.15, Callister 6e.
(Fig. 13.15 is from W.D. Kingery, H.K.
Bowen, and D.R. Uhlmann,
Introduction to Ceramics, 2nd ed.,
John Wiley and Sons, Inc., 1976, p.
483.)
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CERAMIC FABRICATION METHODS-III
CEMENTATION
• Produced in extremely large quantities.
• Portland cement:
--mix clay and lime bearing materials
--calcinate (heat to 1400C)
--primary constituents:
tri-calcium silicate
di-calcium silicate
• Adding water
--produces a paste which hardens
--hardening occurs due to hydration (chemical reactions
with the water).
• Forming: done usually minutes after hydration begins.
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SUMMARY
• Fabrication techniques for metals
- Forming, casting, joining
• Hardenability
- Increases with alloy content
• Fabrication techniques for ceramics
- Glass forming (impurities affect forming temp.)
- Particulate forming (needed if ductility is limited)
- Cementation (large volume, room T process)
• Heat treating: used to
- Alleviate residual stress from cooling
- Produce fracture-resistant components by putting
surface in compression
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ANNOUNCEMENTS
Reading:
Core Problems:
Self-help Problems:
0