Processes and Equipment;

(1)

Chapter 5. Metal-Casting Processes and Equipment;

Heat Treatment

Prof. Ahn Sung-Hoon ( )

School of Mechanical and Aerospace Engineering

Seoul National University

(2)

Historical casting parts

Korean bronze dagger( ( )) Bronze bell( )

(3)

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.

(4)

Solidification of Metals

(5)

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

(6)

Polycrystalline alpha brass

(7)

Phase diagram ( )

Graphically illustrates the relationships among temperature, composition, and the phase present in a particular alloy system.

L S

O S

L S

L O

C C

C C L S

L

C C

C C L S

S



 





 



Rule

Lever

(8)

Lever-Rule ( )

(9)

Eutectic system, Pb-Sn

(10)

Types of 3-phase invariant reactions

(11)

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( ): Fe ₃ C, C 6.67%, iron carbide( ), brittle

(12)

a-ferrite & austenite

a-ferrite (x 90) Austenite (x325)

(13)

Iron-carbon system (2)

(14)

Eutectoid steel

 a- ferrite: white

 Fe ₃ C: dark

 Lamellar structure (pearlite)

 (x 500)

(15)

1% carbon (hypereutectoid) pearlite steel

 a- ferrite - white

 eutectoid - cementite - blue

 proeutectoid - cementite - violet

 (x 500)

(16)

Classification of ferrous alloys

(17)

Composition and naming steels

(18)

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

C kg C

C C

C kg C

C C

o

4 . 9 is that

%, 94 022 100

. 0 67 . 6

40 . 0 67 . 6

, 5 is that

%, 50 022 100

. 0 77 . 0

022 . 0 40 . 100 0

(%)

, 5 is that

%, 50 022 100

. 0 77 . 0

40 . 0 77 . 100 0

(%)

 



 







 

 



 







 

 





 







 

 



 







 

 





 







 

a g a

a g

a a g

g

(19)

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 Fe

3

C

 Brittle

 White fracture surface( )

Malleable cast iron( )

 Obtained by annealing white cast iron

Compact graphite iron( )

(20)

Cast irons

(21)

Cast irons

(22)

Ternary phase diagram

 Fe-Cr-Ni

(23)

Cast structures

 Pure metal vs. alloys

(24)

Dendrites ( )

(25)

Dendrites

(26)

Fluid flow





vD h h A

A

v A v

A Q

g f v g h p

g v g h p

gh c

v















Re

2 2

constant 2

2

1 2 2

1

2 2 1

1

2 2 2

2 2

1 1

1

2

(27)

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

(28)

Defects/DFM

(29)

Casting alloys

(30)

Applications

(31)

Properties

(32)

Casting processes

 Expendable mold, permanent pattern

 Sand casting

 Shell-mold casting

 Plaster mold casting

 Ceramic mold casting

 Vacuum casting

(33)

Casting processes (2)

 Expendable mold, expendable pattern

 Evaporative-pattern casting (lost foam)

 Investment casting (lost wax)

(34)

Investment casting

(35)

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

(36)

Pressure casting/centrifugal casting

(37)

Die casting

 Hot-chamber process

 Cold-chamber process

(38)

Squeeze casting/single crystal

(39)

Casting for single crystal

floating-zone method Crystal-pulling method

(Czochralski process)

(40)

Heat treatment-ferrous alloys

 Pearlite

 Spheroidite

 Bainite

 Martensite

 Quenching( )

 Body Centered Tetragonal(BCT)

 Retained austenite

 Tempered martensite

(41)

Transformation-ferrous alloys

Austenite

Pearlite (a+Fe

3

C)

(+proeutectic a) Bainite (a+Fe

³

C)

Martensite

Tempered martensite

reheat Quenching Moderate

cooling Slow cooling

(42)

Ferrous alloys

(43)

Shape memory alloy (SMA)

(44)

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)

(45)

Nonferrous alloys/stainless steel (1)

Precipitation hardening ( ), Al-Cu alloy

Age hardening( )

(46)

Nonferrous alloys/stainless steel (2)

 Solution treatment

 Precipitation hardening

 Aging

 Maraging(martensite + aging)

(47)

Case hardening

 Surface hardening

 Carburizing ( )

 Carbonitriding ( )

 Cyaniding ( )

 Nitriding ( )

 Boronizing ( )

 Flame hardening ( )

 Induction hardening ( )

(48)

Annealing ( )/ tempering ( )

 Normalizing( )

(49)

Design consideration (1)

(50)

Design consideration (2)

(51)

Design consideration (3)

(52)

Economics of casting

(53)

Case study

(54)

Bridge design

(55)

Processes and Equipment;

Chapter 5. Metal-Casting Processes and Equipment;

Heat Treatment

Prof. Ahn Sung-Hoon ( )

School of Mechanical and Aerospace Engineering

Seoul National University

Historical casting parts

Korean bronze dagger( ( )) Bronze bell( )

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.

Solidification of Metals

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

Polycrystalline alpha brass

Phase diagram ( )

Graphically illustrates the relationships among temperature, composition, and the phase present in a particular alloy system.

C C

C C L S

L

C C

C C L S

S



 





 



Rule

Lever

Lever-Rule ( )

Eutectic system, Pb-Sn

Types of 3-phase invariant reactions

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( ): Fe 3 C, C 6.67%, iron carbide( ), brittle

a-ferrite & austenite

a-ferrite (x 90) Austenite (x325)

Iron-carbon system (2)

Eutectoid steel

 a- ferrite: white

 Fe 3 C: dark

 Lamellar structure (pearlite)

 (x 500)

1% carbon (hypereutectoid) pearlite steel

 a- ferrite - white

 eutectoid - cementite - blue

 proeutectoid - cementite - violet

 (x 500)

Classification of ferrous alloys

Composition and naming steels

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)

 Cementite( ): Fe ₃ C, C 6.67%, iron carbide( ), brittle

 Fe ₃ C: dark