Download - Phase Transformation of Metals - Manufacturing Laboratoryma.gnu.ac.kr/course/ms/08_Phase_Transformations.pdf · 2017-03-21 · Phase Transformation of Metals (금속의상변태)

© 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


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


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 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 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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현재 이이미지를 표시할 수없습니다 .

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CFe

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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


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


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


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

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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

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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