Phase Transformation of Metals - Manufacturing .2017-03-21  Phase Transformation of Metals...

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  • Su-Jin Kim, GNU

    Phase transformMaterial Science

    Phase Transformation ofMetals

    ()& Heat Treatment

    () 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

    http://www.kocw.net/home/cview.do?lid=c4172fa523eac7a5

    http://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

    (C

    )

    200

    300

    400

    500

    600

    700

    800

    727

    Pearlite

    Bainite

    105

    Martensite

    Temperedmaternsite

    Spheroidite

    ductile

    strong

    isothermal

    continuous cooling

    Fe3C spheres + Fe3C +

    layers

    elongated Fe3C +

    ext. small Fe3C +

    BCT needle +

  • Su-Jin Kim, GNU

    Phase transformMaterial Science

    Phase Transformation of Fe-C Pearlite: slow cool cementite, Fe3C + ferrite, layers (ductile)

    Bainite : moderate cool elongated Fe3C particles + ferrite,

    Martensite: rapid quench BCT(body centered tetragonal) needles + austenite, BCT few slip planes (hard, brittle)

    Tempering: reheat M extremely small Fe3C + (strength, dudtility)

    Spheroidite: Reheat just below eutectoid for long times Fe3C particles + (very ductile)

    5

    .

    .

    xx x

    xx

    x

    CFe

  • Su-Jin Kim, GNU

    Phase transformMaterial Science

    Heat Treatment() of Steel

    1. Annealing ()

    2. Normalizing ()

    3. Quenching ()

    4. Tempering ()

    Time (s)0.1 1 10 100 1000 104

    100

    Tem

    pera

    ture

    (C

    )

    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() 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 200~600C, improve

    thoughness

    Heat Treat. Cooling MicrostructureAnnealing cool slow soft perlite Normalizing open air uniform grain sizeQuenching oil water hard martensiteTempering 200~600C 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 phase

    Water

  • Su-Jin Kim, GNU

    Phase transformMaterial Science

    Time (s)0.1

    1 10

    100 1000

    104100

    Tem

    pera

    ture

    (C

    )

    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 ()

    Al, Pb or Cu based alloy

    11

  • Su-Jin Kim, GNU

    Phase transformMaterial Science

    Aging Hardening Aging Hardening = Precipitation Hardening ():

    2nd phase particles increase strength1. Solution(): get single phase 2. Rapid quench : super saturated 3. Age(): reheat to nucleate small particles within

    phase

    +

    CuAl2,

    Liquid, L

    +

    +L

    0 10 20 30 40 50300

    Composition (wt% Cu)

    Tem

    pera

    ture

    (C

    )

    400

    500

    600

    700

    +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

    y

    Looping200

    400200C > 150C

    1min 1h 1day 1mo