M2794.001800 M A T E R I A L A N D M A N U F A C T U R I N G P R O C E S S E S
Chapter 5. Metal-Casting
Processes and Equipment;
Heat Treatment
Prof. Ahn Sung-Hoon ( )
School of Mechanical and Aerospace Engineering
Seoul National University
© Prof. Ahn, Sung-Hoon
Historical casting parts
Korean bronze dagger( ( ))
& molds( )
Bronze bell( )
2
© Prof. Ahn, Sung-Hoon
Casting
Casting is a manufacturing process by which a molten material such as metal or
plastic is introduced into a mold made of sand or metal, allowed to solidify within
the mold, and then ejected or broken out to make a fabricated part.
Advantages
Making parts of complex shape in a single piece.
Producing large number of identical castings within specified tolerances.
Good bearing qualities and jointless product.
Disadvantages
Limitations of mechanical properties because of the polycrystalline grain structure.
Poor dimensional accuracy due to shrinkage of metal during solidification.
If the number of parts cast is relatively small, the cost per casting increases rapidly.
Fundamental aspects in casting operations
Solidification of the metal from its molten state.
Flow of the molten metal into the mold cavity.
Heat transfer during solidification and cooling of the metal in the mold.
Mold material and its influence on the casting process.
3
© Prof. Ahn, Sung-Hoon
Solidification of Metals4
© Prof. Ahn, Sung-Hoon
Solid solution Solute( )
Solvent( )
When the particular crystal structure of the solvent is maintained during alloying,
the alloy is called solid solution. Substitutional solid solution( )
Interstitial solid solution( )
5.2.2 Intermetallic compound( ) Complex structures in which solute atoms are present among solvent atoms in certain specific
proportions.
5.2.3 Two-phase system( ) Phase: a homogeneous portion of a system that has uniform physical and chemical characteristics
5
© Prof. Ahn, Sung-Hoon
Polycrystalline alpha brass 6
© Prof. Ahn, Sung-Hoon
Phase diagram ( )
Graphically illustrates the relationships among temperature, composition,
and the phase present in a particular alloy system.
LS
OS
LS
LO
CC
CC
LS
L
CC
CC
LS
S
RuleLever
7
© Prof. Ahn, Sung-Hoon
Lever-Rule ( )8
© Prof. Ahn, Sung-Hoon
Eutectic system, Pb-Sn9
© Prof. Ahn, Sung-Hoon
Types of 3-phase invariant reactions10
© Prof. Ahn, Sung-Hoon
Iron-carbon system (1)
Pure iron( ) : 0.008% C
Steels( ) : 2.11% C
Cast irons( ) : ~6.67% C
a-ferrite( ): BCC, soft and ductile
d-ferrite: BCC, stable only at very high temperatures
Austenite( ) : FCC, ductile
Cementite( ): Fe3C, C 6.67%, iron carbide( ), brittle
11
© Prof. Ahn, Sung-Hoon
a-ferrite & austenite
a-ferrite (x 90) Austenite (x325)
12
© Prof. Ahn, Sung-Hoon
Iron-carbon system (2)13
© Prof. Ahn, Sung-Hoon
Eutectoid steel
a- ferrite: white
Fe3C: dark
Lamellar structure
(pearlite)
(x 500)
14
© Prof. Ahn, Sung-Hoon
1% carbon (hypereutectoid) pearlite steel
a- ferrite - white
eutectoid - cementite -
blue
proeutectoid -
cementite - violet
(x 500)
15
© Prof. Ahn, Sung-Hoon
Classification of ferrous alloys16
© Prof. Ahn, Sung-Hoon
Composition and naming steels17
© Prof. Ahn, Sung-Hoon
Amount of phases in carbon steel
Casting 1040 steel 10kg, calculate a phase and g phase at (a) 900 C,
(b) 728 C and (c) 726 C
(a) Austenite:100% g
(b)
(c) kg
kgCC
CC
kgCC
CC
o
o
4.9 is that %,94100022.067.6
40.067.6
,5 is that %,50100022.077.0
022.040.0100(%)
,5 is that %,50100022.077.0
40.077.0100(%)
a
g
a
ag
a
ag
g
18
© Prof. Ahn, Sung-Hoon
Cast irons
Fe, C 2.11~4.5%, Si ~3.5%
According to solidification
morphology :
Gray cast iron( ) Flake graphite( )
Gray fracture surface( )
Damping( )
Ductile(nodular) iron( ) Ductile
White cast iron( ) Large amount of Fe3C
Brittle White fracture surface( )
Malleable cast iron( ) Obtained by annealing white cast iron
Compact graphite iron( )
19
© Prof. Ahn, Sung-Hoon
Cast irons20
© Prof. Ahn, Sung-Hoon
Cast irons21
© Prof. Ahn, Sung-Hoon
Ternary phase diagram
Fe-Cr-Ni
22
© Prof. Ahn, Sung-Hoon
Cast structures
Pure metal vs. alloys
23
© Prof. Ahn, Sung-Hoon
Dendrites ( )24
© Prof. Ahn, Sung-Hoon
Dendrites25
© Prof. Ahn, Sung-Hoon
Fluid flow
vD
h
h
A
A
vAvAQ
fg
v
g
ph
g
v
g
ph
g
v
g
ph
ghcv
Re
22
constant2
2
1
2
2
1
2211
2
222
2
111
2
26
© Prof. Ahn, Sung-Hoon
Solidification time & shrinkage
Chvonrinov’s rule
Solidification time
= C(volume/surface area)2
Shrinkage occurs at
Molten metal
Phase change
Solid metal
Cast iron expands
Graphite has high volume/mass
Net expansion during
precipitation
Similarly Bi-Sn alloys expand
27
© Prof. Ahn, Sung-Hoon
Defects/DFM28
© Prof. Ahn, Sung-Hoon
Casting alloys29
© Prof. Ahn, Sung-Hoon
Applications30
© Prof. Ahn, Sung-Hoon
Properties31
© Prof. Ahn, Sung-Hoon
Casting processes
Expendable mold,
permanent pattern
Sand casting
Shell-mold casting
Plaster mold casting
Ceramic mold casting
Vacuum casting
32
© Prof. Ahn, Sung-Hoon
Casting processes (2)
Expendable mold, expendable pattern
Evaporative-pattern casting (lost foam)
Investment casting (lost wax)
33
© Prof. Ahn, Sung-Hoon
Investment casting34
© Prof. Ahn, Sung-Hoon
Casting processes (3)
Permanent mold
Slush casting
Pressure casting
Die casting
Centrifugal casting
Squeeze casting
Semisolid metal forming
Casting for single crystal
Rapid solidification
In permanent-mold casting, a mold are
made from materials such as steel,
bronze, refractory metal alloys, or
graphite. Because metal molds are better
heat conductors than expendable molds,
the solidifying casting is subjected to a
higher rate of cooling, which turn affects
the microstructure and grain size within
the casting.
Cooling methods : water, air-cooled fin
Used for aluminum, magnesium, and
copper alloys due to their lower melting
points
Pros : good surface finishing, close
dimensional tolerances, and uniform and
good mechanical properties
Cons : not economical for small
production runs, not good for intricate
shapes
35
© Prof. Ahn, Sung-Hoon
Pressure casting/centrifugal casting36
© Prof. Ahn, Sung-Hoon
Die casting
Hot-chamber process
Cold-chamber process
37
© Prof. Ahn, Sung-Hoon
Squeeze casting/single crystal38
© Prof. Ahn, Sung-Hoon
Casting for single crystal
floating-zone
method
Crystal-pulling method(Czochralski process)
39
© Prof. Ahn, Sung-Hoon
Heat treatment-ferrous alloys
Pearlite
Spheroidite
Bainite
Martensite
Quenching( )
Body Centered Tetragonal(BCT)
Retained austenite
Tempered martensite
40
© Prof. Ahn, Sung-Hoon
Transformation-ferrous alloys
Austenite
Pearlite
(a+Fe3C)
(+proeutectic a) Bainite
(a+Fe3C)
Martensite
Tempered
martensite
reheat
Quenching
Moderate
cooling
Slow cooling
41
© Prof. Ahn, Sung-Hoon
Ferrous alloys42
© Prof. Ahn, Sung-Hoon
Shape memory alloy (SMA)43
© Prof. Ahn, Sung-Hoon
Quenched AISI 9310 steel
The white strikes are
excess proeutectoid
cemetite
Cream color is
retained austenite
Gray area is bainite
Blue/brown regions
are martensite
(x 320)
44
© Prof. Ahn, Sung-Hoon
Nonferrous alloys/stainless steel (1)
Precipitation hardening
( ), Al-Cu alloy
Age hardening( )
45
© Prof. Ahn, Sung-Hoon
Nonferrous alloys/stainless steel (2)
Solution treatment
Precipitation hardening
Aging
Maraging(martensite + aging)
46
© Prof. Ahn, Sung-Hoon
Case hardening
Surface hardening
Carburizing ( )
Carbonitriding ( )
Cyaniding ( )
Nitriding ( )
Boronizing ( )
Flame hardening ( )
Induction hardening ( )
47
© Prof. Ahn, Sung-Hoon
Annealing ( )/ tempering ( )
Normalizing( )
48
© Prof. Ahn, Sung-Hoon
Design consideration (1)49
© Prof. Ahn, Sung-Hoon
Design consideration (2)50
© Prof. Ahn, Sung-Hoon
Design consideration (3)51
© Prof. Ahn, Sung-Hoon
Economics of casting52
© Prof. Ahn, Sung-Hoon
Case study53
© Prof. Ahn, Sung-Hoon
Bridge design54
© Prof. Ahn, Sung-Hoon
Material of the bridge
Another bridge
55
Top Related