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Chapter 11 - 1
Steel and cast iron
Chapter 11 - 2
2
Chapter 11 - 3
Adapted from Fig. 11.1, Callister 7e.
Taxonomy of Metals
Metal Alloys
Steels
Ferrous Nonferrous
Cast Irons Cu Al Mg Ti<1.4wt%C 3-4.5wt%CSteels
<1.4wt%CCast Irons3-4.5wt%C
Fe3C cementite
1600
1400
1200
1000
800
600
4000 1 2 3 4 5 6 6.7
L
gaustenite
g+L
g+Fe3Ca
ferritea+Fe3C
a+g
L+Fe3C
d
(Fe) Co , wt% C
Eutectic:
Eutectoid:0.76
4.30
727°C
1148°C
T(°C) microstructure:ferrite, graphite cementite
Chapter 11 - 4
1. Other terms: plain steel, mild steel, low-carbon steel
2. Available in almost all product forms: e.g. sheet, strip, bar, plate, tube, pipe etc.
3. Designation: e.g. 1040 steel - 0.40 wt% C4. Up to 2 wt% C5. Limitation for other alloying elements:
Si up to 0.6 %,Cu up to 0.6 %Mn up to 1.65 %
Carbon steel
3
Chapter 11 - 5
Chapter 11 - 6
t11_01b_pg361
Hot-rolled steels and typical applications
4
Chapter 11 - 7
AISI: the American Iron and Steel Institute
SAE: the Sociaty of Automotive and Engineering
ASTM: the American Society for Testing and Materials
UNS: the Uniform Numbering System
Chapter 11 - 8
High alloys:
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Chapter 11 - 9
Chapter 11 -10
Designations, compositions and applications for six tool steels
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Chapter 11 -11
Chapter 11 -12
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Chapter 11 -13
Chapter 11 -14
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Chapter 11 -15
Stainless steels
1. More resistant to rusting and staining than carbon- and low-alloy steels
2. Chromium addition, usually above 10 wt% (4-30%)
Chapter 11 -16
Stainless steels
9
Chapter 11 -17
Chapter 11 -18
10
Chapter 11 -19Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e.
Steels
Low Alloy High Alloy
low carbon <0.25wt%C
Med carbon0.25-0.6wt%C
high carbon 0.6-1.4wt%C
Uses auto struc. sheet
bridges towers press. vessels
crank shafts bolts hammers blades
pistons gears wear applic.
wear applic.
drills saws dies
high T applic. turbines furnaces V. corros. resistant
Example 1010 4310 1040 4340 1095 4190 304
Additions noneCr,VNi, Mo
noneCr, Ni Mo
noneCr, V, Mo, W
Cr, Ni, Mo
plain HSLA plainheat
treatableplain tool
austenitic stainless
Name
Hardenability 0 + + ++ ++ +++ 0TS - 0 + ++ + ++ 0EL + + 0 - - -- ++
increasing strength, cost, decreasing ductility
Chapter 11 -20
Ferrous Alloys
Iron containing – Steels - cast irons
Nomenclature AISI & SAE
10xx Plain Carbon Steels11xx Plain Carbon Steels (resulfurized for machinability)
15xx Mn (10 ~ 20%)
40xx Mo (0.20 ~ 0.30%)
43xx Ni (1.65 - 2.00%), Cr (0.4 - 0.90%), Mo (0.2 - 0.3%)
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
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Chapter 11 -21
Cast Iron
• Ferrous alloys with > 2.1 wt% C– more commonly 3 - 4.5 wt%C
• low melting (also brittle) so easiest to cast
• Cementite decomposes to ferrite + graphiteFe3C 3 Fe (a) + C (graphite)
– cementite (Fe3C) a metastable phase– graphite formation promoted by
• Si > 1 wt%• slow cooling
Chapter 11 -22
Fe-C True Equilibrium DiagramGraphite formation promoted by
• Si > 1 wt%
• slow cooling
1600
1400
1200
1000
800
600
4000 1 2 3 4 90
L
g+L
a + Graphite
Liquid +Graphite
(Fe) Co, wt% C
0.65
740°C
T(°C)
g+ Graphite
100
1153°CgAustenite 4.2 wt% C
a + g
Cast iron1. Gray iron2. Nodular (ductile) iron3. White iron4. Malleable iron5. Compacted graphite iron
(CGI)
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Chapter 11 -23
Types of Cast IronGray iron
– 1 - 3 % Si, 2.5 – 4% C– graphite flakes plus ferrite/pearlite– brittleness due to the flake-like graphite
• weak & brittle under tension• stronger under compression• excellent vibrational dampening• wear resistant
Ductile (nodular) iron
– a small amount (0.05 wt%) of Mg or Ce– spheroidal graphite precipitates (nodules)
rather than flakes– matrix often pearlite or ferrite– Ductility increased by a factor of 20, strength
is doubled
Chapter 11 -24
Optical micrograph of a grey iron (Fe-3.3C-2.1Si-0.5Cr-0.5Mo-1.0Cu)
Microstructure of pearlite in the grey iron (Fe-3.3C-2.1Si-0.5Cr-0.5Mo-1.0Cu). TEM.
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Chapter 11 -25
(a) steel; (b) grey cast iron
Chapter 11 -26
Types of Cast IronWhite iron
– <1wt% Si, harder but brittle– eutectic carbide plus pearlite– large amount of Fe3C formed during
casting
Malleable iron
– the result of annealing white iron castings, 800º-900º C
– cementite→ graphite precipitates, clusters or rosettes
– more ductile
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Chapter 11 -27
Types of Cast Iron
Compacted graphite iron (CGI)
1. C: 3.1-4.0%, Si: 1.7-3.0%2. Lower content of Mg or Ce3. Worm-like (vermicular)
graphite particles
• higher thermal conductivity• better resistance to thermal shock• lower oxidation at elevated
temperature
Chapter 11 -28
Production of Cast Iron
Adapted from Fig.11.5, Callister 7e.
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Chapter 11 -29
Cast iron
Chapter 11 -30
Which type of cast iron is in the pictures illustrated below ?
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Chapter 11 -31
Limitations of Ferrous Alloys
1) Relatively high density2) Relatively low conductivity3) Poor corrosion resistance
Chapter 11 -32
Metal Fabrication
• How do we fabricate metals?– Blacksmith - hammer (forged)– Molding - cast
• Forming Operations – Rough stock formed to final shape
Hot working vs. Cold working• T high enough for • well below Tm
recrystallization • work hardening
• Larger deformations • smaller deformations
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Chapter 11 -33
FORMING
roll
AoAd
roll
• Rolling (Hot or Cold Rolling)(I-beams, rails, sheet & plate)
Ao Ad
force
dieblank
force
• Forging (Hammering; Stamping)(wrenches, crankshafts)
often atelev. T
Adapted from Fig. 11.8, Callister 7e.
Metal Fabrication Methods - I
ram billet
container
containerforce
die holder
die
Ao
Adextrusion
• Extrusion(rods, tubing)
ductile metals, e.g. Cu, Al (hot)
tensile force
AoAddie
die
• Drawing(rods, wire, tubing)
die must be well lubricated & clean
CASTING JOINING
Chapter 11 -34
FORMING CASTING JOINING
Metal Fabrication Methods - II
• Casting- mold is filled with metal– metal melted in furnace, perhaps alloying
elements added. Then cast in a mold – most common, cheapest method– gives good production of shapes– weaker products, internal defects– good option for brittle materials
18
Chapter 11 -35
• Sand Casting(large parts, e.g.,auto engine blocks)
Metal Fabrication Methods - II
• trying to hold something that is hot
• what will withstand >1600ºC?
• cheap - easy to mold => sand!!!
• pack sand around form (pattern) of desired shape
Sand Sand
molten metal
FORMING CASTING JOINING
Chapter 11 -36
plasterdie formedaround waxprototype
• Sand Casting(large parts, e.g.,auto engine blocks)
• Investment Casting(low volume, complex shapese.g., jewelry, turbine blades)
Metal Fabrication Methods - II
Investment Casting
• pattern is made from paraffin.
• mold made by encasing in plaster of paris
• melt the wax & the hollow mold is left
• pour in metal
wax
FORMING CASTING JOINING
Sand Sand
molten metal
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Chapter 11 -37
plasterdie formedaround waxprototype
• Sand Casting(large parts, e.g.,auto engine blocks)
• Investment Casting(low volume, complex shapese.g., jewelry, turbine blades)
Metal Fabrication Methods - II
wax
• Die Casting(high volume, low T alloys)
• Continuous Casting(simple slab shapes)
molten
solidified
FORMING CASTING JOINING
Sand Sand
molten metal
Chapter 11 -38
CASTING JOINING
Metal Fabrication Methods - III
• Powder Metallurgy(materials w/low ductility)
pressure
heat
point contact at low T
densificationby diffusion at higher T
area contact
densify
• Welding(when one large part isimpractical)
• Heat affected zone:(region in which themicrostructure has beenchanged).
Adapted from Fig. 11.9, Callister 7e.(Fig. 11.9 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.)
piece 1 piece 2
fused base metal
filler metal (melted)base metal (melted)
unaffectedunaffectedheat affected zone
FORMING
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Chapter 11 -39
Annealing: Heat to Tanneal, then cool slowly.
Based on discussion in Section 11.7, Callister 7e.
Thermal Processing of Metals
Types of Annealing
• Process Anneal:Negate effect of cold working by (recovery/ recrystallization)
• Stress Relief: Reducestress caused by:
-plastic deformation -nonuniform cooling -phase transform.
• Normalize (steels): Deform steel with largegrains, then normalizeto make grains small.
• Full Anneal (steels): Make soft steels for good forming by heating to get g, then cool in furnace to get coarse P.
• Spheroidize (steels): Make very soft steels for good machining. Heat just
below TE & hold for15-25 h.
Chapter 11 -40
a) Annealing
b) Quenching
Heat Treatments
c)
c) Tempered Martensite
Adapted from Fig. 10.22, Callister 7e.
time (s)10 10 3 10 510 -1
400
600
800
T(°C)
Austenite (stable)
200
P
B
TE
0%
100%50%
A
A
M + A
M + A
0%
50%
90%
a)b)
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Chapter 11 -41f11_10_pg389
Chapter 11 -42
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Chapter 11 -43
Hardenability--Steels
• Ability to form martensite• Jominy end quench test to measure hardenability.
• Hardness versus distance from the quenched end.
Adapted from Fig. 11.11, Callister 7e. (Fig. 11.11 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.)
Adapted from Fig. 11.12, Callister 7e.
24°C water
specimen (heated to gphase field)
flat ground
Rockwell Chardness tests
Har
dnes
s, H
RC
Distance from quenched end
Chapter 11 -44
• The cooling rate varies with position.
Adapted from Fig. 11.13, Callister 7e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)
Why Hardness Changes With Position
distance from quenched end (in)Har
dnes
s, H
RC
20
40
60
0 1 2 3
600
400
200A fi M
A fiP
0.1 1 10 100 1000
T(°C)
M(start)
Time (s)
0
0%100%
M(finish) Martensite
Martensite + Pearlite
Fine Pearlite
Pearlite
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Chapter 11 -45
Hardenability vs Alloy Composition• Jominy end quench
results, C = 0.4 wt% C(table 11.2a p363)
• "Alloy Steels"(4140, 4340, 5140, 8640)--contain Ni, Cr, Mo
(0.2 to 2wt%)--these elements shift
the "nose".--martensite is easier
to form.
Adapted from Fig. 11.14, Callister 7e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.)
Cooling rate (°C/s)
Har
dnes
s, H
RC
20
40
60
100 20 30 40 50Distance from quenched end (mm)
210100 3
4140
8640
5140
1040
50
80
100
%M4340
T(°C)
10-1 10 103 1050
200
400
600
800
Time (s)
M(start)M(90%)
shift from A to B due to alloying
BA
TE
Chapter 11 -46
• Effect of quenching medium:
Mediumairoil
water
Severity of Quenchlow
moderatehigh
Hardnesslow
moderatehigh
• Effect of geometry:When surface-to-volume ratio increases:
--cooling rate increases--hardness increases
Positioncentersurface
Cooling ratelowhigh
Hardnesslowhigh
Quenching Medium & Geometry
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Chapter 11 -47
• Steels: increase TS, Hardness (and cost) by adding--C (low alloy steels)--Cr, V, Ni, Mo, W (high alloy steels)--ductility usually decreases with additions.
• Non-ferrous:--Cu, Al, Ti, Mg, Refractory, and noble metals.
• Fabrication techniques:--forming, casting, joining.
• Hardenability--increases with alloy content.
• Precipitation hardening--effective means to increase strength in
Al, Cu, and Mg alloys.
Summary
