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    Alloys and Their Phase Diagram

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    abskumar
    This document discusses phase diagrams and alloys. It begins by introducing Gibbs phase rule and using water as a simple example. It then discusses binary alloy systems, including isomorphous and eutectic systems. Key concepts explained include lever rule, cooling curves, and eutectic microstructures. The focus is then on the iron-iron carbide system and steel alloys. Plain carbon steels are discussed and the concepts of hypoeutectoid and hypereutectoid compositions. Microstructures resulting from slow cooling are illustrated. Sample problems are provided to calculate phase amounts.

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    Alloys and Their Phase Diagram

    Uploaded by

    abskumar
    2K views45 pages
    This document discusses phase diagrams and alloys. It begins by introducing Gibbs phase rule and using water as a simple example. It then discusses binary alloy systems, including isomorphous and eutectic systems. Key concepts explained include lever rule, cooling curves, and eutectic microstructures. The focus is then on the iron-iron carbide system and steel alloys. Plain carbon steels are discussed and the concepts of hypoeutectoid and hypereutectoid compositions. Microstructures resulting from slow cooling are illustrated. Sample problems are provided to calculate phase amounts.

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    This document discusses phase diagrams and alloys. It begins by introducing Gibbs phase rule and using water as a simple example. It then discusses binary alloy systems, including isomorphous and eutectic systems. Key concepts explained include lever rule, cooling curves, and eutectic microstructures. The focus is then on the iron-iron carbide system and steel alloys. Plain carbon steels are discussed and the concepts of hypoeutectoid and hypereutectoid compositions. Microstructures resulting from slow cooling are illustrated. Sample problems are provided to calculate phase amounts.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    2K views45 pages

    Alloys and Their Phase Diagram

    Uploaded by

    abskumar
    This document discusses phase diagrams and alloys. It begins by introducing Gibbs phase rule and using water as a simple example. It then discusses binary alloy systems, including isomorphous and eutectic systems. Key concepts explained include lever rule, cooling curves, and eutectic microstructures. The focus is then on the iron-iron carbide system and steel alloys. Plain carbon steels are discussed and the concepts of hypoeutectoid and hypereutectoid compositions. Microstructures resulting from slow cooling are illustrated. Sample problems are provided to calculate phase amounts.

    Copyright:

    Attribution Non-Commercial (BY-NC)
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 45
    At a glance
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    The document discusses phase diagrams and alloy systems. It covers concepts like the Gibbs phase rule, types of solubility, binary eutectic alloys, and phase diagrams of steel.

    The Gibbs phase rule relates the number of phases, components, and degrees of freedom in a system. It is used to determine the number of variables that can be independently varied in a system at equilibrium.

    There are four main types of solubility discussed: unlimited solubility, limited solubility, no solubility, and intermediate phases.

    Alloys & Their

    Phase Diagrams
    Objectives of the class

    Gibbs phase rule


    Introduction to phase diagram
    Practice phase diagram
    Lever rule
    Important Observation: One question in the
    midterm
    Gibbs phase rule

    P + F = C +2

    P: number of phases (ie, solid, liquid, or gas)


    C: number of components
    F: Degree of freedom
    Simple
    p Example
    p
    Water:
    a)) At the
    th ttriple
    i l point:
    i t
    P = 3 (solid, liquid, and gas)
    C= 1 (water)
    P+F=C+2
    F = 0 (no degree of freedom)

    b) liquid-solid curve
    P=2
    2+F = 1 + 2
    F= 1
    One variable ((T or P)) can be changed
    g

    c) Liquid
    P =1
    So F =2
    Two variables (T and P) can be varied independently
    and the system will remains a single phase
    Unlimited Solutibity
    Limited solubility
    No Solubility
    Binary Isomorphous Alloy Systems

    A mixture of two metals is called a


    binary alloy and constitutes a
    two-component
    two component system.
    Each metallic element in an alloy is
    called
    ll d a separate
    t component. t
    Isomorphous
    p systems
    y contain
    metals which are completely
    soluble in each other and have a
    single type of crystal structure.
    C -Ni:
    Cu
    Cu- Ni A Substitutional
    S b tit ti l Solid
    S lid
    Solution
    Cu--Ni: Binary Isomorphous Alloy Example
    Cu

    Liquidus line

    S lid line
    Solidus li

    Tie line
    Cu--Ni: Cooling Curves
    Cu
    Cooling curve
    The Lever Rule
    To compute the amount of solid phase:

    Fraction of the solid phase = (Wo – Wl)/(Ws-Wl)


    Some examples
    Binary Eutectic Alloy Systems
    Eutectic composition:

    Phases: alpha and beta

    Composition of the phases:


    Alpha: 19.2% Sn
    Beta: 97.5% Sn

    Amount of phases:
    45.5% of alpha: (97.5-61.9)/(97.5-19.2)
    (97.5 61.9)/(97.5 19.2)
    54.5% of beta phase
    Example: Point D

    Ph
    Phases: li id and
    liquid d alpha
    l h

    Composition of the phases:


    Alpha: 19.2% Sn
    Liquid: 61.9% Sn

    Amount of phases:
    51% of alpha phase: (61.9-40)/(61.9-19.2)
    (61.9 40)/(61.9 19.2)
    49% of liquid phase
    Example: Point E

    Ph
    Phases: alpha
    l h and
    d beta
    b t

    Composition of the phases:


    Alpha: 19.2% Sn
    beta: 97.5% Sn

    Amount of phases:
    73% of alpha phase: (97.5-40)/(97.5-19.2)
    (97.5 40)/(97.5 19.2)
    27% of beta phase
    So what?
    High-melting
    Plumbers’ solder: pasty used in joints (Romans) and car body filling

    solder
    ld

    Soft: eutectic (free flowing): electronic assemby


    E
    Eutetic:
    i from
    f the
    h Greek
    G k
    easy melting
    A Eutectic Cooling
    g Curve

    Temperature-time cooling curve


    for 60% Pb – 40% Sn alloy
    Eutectic Microstructures

    There are a number of different


    morphologies#” for the two phases in a
    “morphologies
    binary eutectic alloy.
    Of prime
    i importance
    i t is
    i the
    th minimization
    i i i ti off
    the interfacial area between the phases.
    The rate of cooling can also have an
    important effect.
    effect
    Eutectic Microstructures
    Schematic illustration of the
    various eutectic
    microstructures: (a)
    lamellar, (b) rodlike,
    lamellar rodlike (c)
    globular, and (d) acicular
    (or needlelike).
    Morphology means the
    “form”,, “shape”
    p or
    “outward microstructure”
    of a phase.
    Microstructure evolution
    Equilibrium Microstructure
    of Steel Alloys
    The Iron-Iron Carbide Phase Diagram

    Austenite
    FCC crystal

    α ferrite
    BCC iron crystal lattice
    Cementite
    Hard and brittle
    Steels and Irons
    Forging
    Forging
    Plain-Carbon Steel
    Steel can be defined as an Iron alloy which transforms to
    Austenite on heating.
    A plain-carbon steels has no other major alloying element beside
    carbon.
    b
    When a plain-carbon steel is slowly cooled from the Austenitic
    range it undergoes the eutectoid transformation.
    Construction steel alloys used for concrete reinforcing bars and
    structural shapes have been traditionally been 0.1-0.2% C plain-
    carbon steels with only minor additional elements, (this is now
    changing as the steel industry becomes more sophisticated). In
    general these alloys
    g y are called Low
    Low--alloyy Steel and for most
    purposes they can be considered plain-carbon steel.
    The Iron-Iron Carbide Eutectoid System

    Note: pearlite is not a phase, but a combination of ferrite and cementite


    Eutectoid
    Eutectoid Microstructures
    Just like the eutectic systems there are a number of different
    “morphologies#” for the two phases in a binary eutectic
    alloy.
    The most common morphology for eutectoid areas in the Fe-
    Fe3C system is lamellar
    lamellar. (This is because most steel is
    relatively slowly cooled through the eutectoid phase
    transformation.)
    Evolution of Eutectoid Steel Microstructure

    Hypo
    Hyp oeutectoid Hyp
    Hyper
    ereutectoid
    eutectoid
    Slow Cooling
    g of Plain-Carbon Steels
    Transformation of a 0.4% C hypoeutectoid plain-carbon
    steel with slow cooling.
    cooling
    Hypoeutectoid
    Slow Cooling of Plain-Carbon Steels
    Transformation of a 1.2% C hypereutectoid plain-carbon steel
    with slow cooling.
    g
    Hypereutectoid
    Carbon Steel (90% of the steel production)

    Low alloy steel (up to 6% of


    chromium, nickel, etc)
    St i l
    Stainless steel
    t l (18% chromium
    h i and
    d
    8% nickel)
    Tool steels ( heavy alloyed with
    chromium, molybdenum, tungsten,
    vanadium, and cobalt).
    Problem
    A 0.45%C hypoeutectoid plain-carbon steel is slowly
    cooled from 950 C to a temperature just slightly
    above 723 C. Calculate the weight percent austenite
    and weight percent proeutectoid ferrite in this steel.

    0.45 Austenite = (0.45-0.02)/(0.80-0.02


    P
    Proeutectoid
    t t id Ferrite
    F it =(0.80-0.45)
    (0 80 0 45)
    = 44.
    0.80
    0.02
    A 0.45%C hypoeutectoid plain-carbon steel is slowly
    cooled from 950 C to a temperature just slightly
    below 723 C C.
    (a)Calculate the weight percent proeutectoid ferrite in
    this steel.
    (b) Calculate the weight percent eutectoid ferrite and
    the weight percent eutectoid cementite in this steel.
    0.45 Proeutectoid Ferrite =(0.80-0.45)/(0.8-0.02)
    =44.9%
    Cementite = (0.45-0.02)/(6.67-0.02)
    (0 45-0 02)/(6 67-0 02) = 6
    6.5%
    5%

    0.02 0.80 Total ferrite = ((6.67-0.45)/(6.67-0.02)


    )( ) = 93.5%
    Eutectoid ferrite =
    total ferrite – proeutectoid ferrite
    = 93.5 – 44.9 = 48.6%
    Problem
    A hypoeutectoid steel contains 22.5%
    eutectoid ferrite. What is the average
    carbon content?
    Total ferrite= proeutectoid ferrite + eutectoid ferrite
    (6.67-x)/(6.67-0.02) = (0.80 –x)/(0.8-0.02) + 0.225

    X =0.2
    Jominy Hardenability Test
    Intermediate Phases - Cu-Zn Example
    Hypoeutectoid Phase Diagram
    If a steel with a composition x% carbon is cooled from the
    Austenite region
    g at about 770 °C ferrite beginsg to form. This is
    called pro
    proeutectoid (or pre
    pre--eutectoid) ferrite since it forms
    before the eutectoid temperature.

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