phase transformation of metals - manufacturing...
TRANSCRIPT
© Su-Jin Kim, GNU
Phase transformMaterial Science
Phase Transformation ofMetals
(금속의상변태)& Heat Treatment
(열처리) Associate Professor Su-Jin Kim
School of Mechanical EngineeringGyeongsang National University
© Su-Jin Kim, GNU
Phase transformMaterial Science
OCWSteel hammering heat treat(Quenching)https://youtu.be/98lh5Q0M0cg
Steel Heat Treatment (Tempering, Normalizing, Annealing)https://youtu.be/3_BH6HqpPtk
Aluminum crystal grain dislocation forming heat treatment (recrystallization grain-growth CuAl2 aging)https://youtu.be/BBFBJ1zJlmA
© Su-Jin Kim, GNU
Phase transformMaterial Science
KOCW
열처리http://www.kocw.net/home/cview.do?lid=c4172fa523eac7a5
상변태http://www.kocw.net/home/cview.do?lid=a8608b01a05f49f4http://www.kocw.net/home/cview.do?lid=9019eb45020e5c92http://www.kocw.net/home/cview.do?lid=d4551cd63a1a63ad
© Su-Jin Kim, GNU
Phase transformMaterial Science
Phase Transformation of Fe-C• Time & Temperature Microstructure Properties
0.1 1 10 100 1000 104100
Time (s)
Tem
pera
ture
(ºC
)
200
300
400
500
600
700
800
727
Pearlite
Bainite
105
Martensite
Temperedmaternsite
Spheroidite
ductile
strong
isothermal
continuous cooling
Fe3C spheres + αFe3C + α
layers
elongated Fe3C + α
ext. small Fe3C + α
BCT needle + γ
© Su-Jin Kim, GNU
Phase transformMaterial Science
Phase Transformation of Fe-C• Pearlite: slow cool cementite, Fe3C + ferrite, α layers (ductile)
• Bainite : moderate cool elongated Fe3C particles + ferrite, α
• Martensite: rapid quench BCT(body centered tetragonal) needles + austenite, γBCT few slip planes (hard, brittle)
• Tempering: reheat M extremely small Fe3C + α (strength↓, dudtility↑)
• Spheroidite: Reheat just below eutectoid for long times Fe3C particles + α (very ductile)
5
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CFe
© Su-Jin Kim, GNU
Phase transformMaterial Science
Heat Treatment(열처리) of Steel
1. Annealing (풀림)
2. Normalizing (불림)
3. Quenching (담금질)
4. Tempering (뜨임)
Time (s)0.1 1 10 100 1000 104100
Tem
pera
ture
(ºC
)
200
300
400
500
600
700
800
727
1. Annealing
105
3. Quenching 4. Tempering
2. Normalizing
Oil, water Air Heater
© Su-Jin Kim, GNU
Phase transformMaterial Science
Heat Treatment(열처리) of Steel
1. Annealing : refine microstructure (for cold working)2. Normalizing: open air, uniform grain size3. Quenching: oil water, hard martensite, non-ferrous
alloys become soft4. Tempering: reheat martensite 200~600ºC, improve
thoughness
Heat Treat. Cooling MicrostructureAnnealing cool slow soft perlite Normalizing open air uniform grain sizeQuenching oil water hard martensiteTempering 200~600ºC ductile martensite
© Su-Jin Kim, GNU
Phase transformMaterial Science
Hardenability of Steels• Hardenability : measure of the ability to form martensite• Jominy end quench test used to measure hardenability• End quench by water & measure Rc harness• Plot hardness versus distance from the quenched end
Har
dnes
s, H
RC
Distance from quenched end
Steel heated to austenite γphase
Water
© Su-Jin Kim, GNU
Phase transformMaterial Science
Time (s)0.1
1 10
100 1000
104100
Tem
pera
ture
(ºC
)
200
300
400
500
600
700
800
20
105
1 5
Distance from quench end
Har
dnes
s (H
RC
)
S40C SM40C
Hardness with Dist. & Alloy
• The cooling rate decreases with distance from quenched end.
• Alloy steel shift phase transition diagram to longer times martensite is easier to form
Alloy
© Su-Jin Kim, GNU
Phase transformMaterial Science
Heat treatment Furnace
PIT Furnace
Gas
Induction hardeningVacuum
© Su-Jin Kim, GNU
Phase transformMaterial Science
Aging Hardening (시효경화)
Al, Pb or Cu based alloy
11
© Su-Jin Kim, GNU
Phase transformMaterial Science
Aging Hardening• Aging Hardening = Precipitation Hardening (석출경화):
2nd phase particles increase strength1. Solution(용체화): get single phase α2. Rapid quench : super saturated α3. Age(시효): reheat to nucleate small θ particles within α
phaseα
α
α+θ
CuAl2, θ
Liquid, L
α
α+θ
α+L
0 10 20 30 40 50300
Composition (wt% Cu)
Tem
pera
ture
(ºC
)
400
500
600
700
θ+L
(Al) (CuAl2)
1.so
lutio
n2.
quen
ch
3.ag
e
© Su-Jin Kim, GNU
Phase transformMaterial Science
Aging time & Yield strength• Aging time increase particle size maximize strength• Increasing temperature accelerates aging treatment• Al2014 alloy Shear of
particle
Time, Particle size (log)
Yiel
d st
reng
th σ
y
Looping200
400200ºC > 150ºC
1min 1h 1day 1mo