Metallurgy Chapter 9: Lamellar Eutectic Structure and Microstructural Developments Quiz
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Questions and Answers

In the Pb-Sn system, which phase is present just below the eutectic temperature (TE)?

  • α phase particles
  • β phase
  • Primary α eutectic
  • α+β phases (correct)

    • For alloys with a composition of 97.8 wt% Sn, what is the microconstituent present just above TE?

  • Primary α eutectic
  • α+β phases
  • β phase (correct)
  • α phase particles

    • What weight percentage of Sn is required for hypoeutectic alloys in the Pb-Sn system?

  • 50% (correct)
  • 18.3%
  • 40%
  • 61.9%

    • What is the weight percentage of Sn for alloys that exhibit primary α eutectic in the Pb-Sn system?

    <p>18.3%</p> Signup and view all the answers

    In the microstructure of alloys with a composition of 97.8 wt% Sn, what is the weight percentage of the β phase?

    <p>0.27%</p> Signup and view all the answers

    At what temperature do α and β phases coexist in the Pb-Sn system?

    <p>$200 °C$</p> Signup and view all the answers

    What is the eutectoid temperature for the Fe-C system?

    <p>727°C</p> Signup and view all the answers

    Which phase is described as 'cementite-hard' in the Fe-C system?

    <p>Fe3C</p> Signup and view all the answers

    At what temperature does proeutectoid ferrite form in the Fe-C system?

    <p>1148°C</p> Signup and view all the answers

    Which phase is predominantly present in hypoeutectoid steel?

    <p>α</p> Signup and view all the answers

    What is the carbon content, in weight percent, of eutectic composition in the Fe-C system?

    <p>6.7%</p> Signup and view all the answers

    What is the amount of pearlite in 200 g?

    <p>105.6 g</p> Signup and view all the answers

    At what temperature does austenite transform into a mixture of austenite and ferrite?

    <p>727°C</p> Signup and view all the answers

    What is the weight percentage of carbon in cementite?

    <p>0.40 wt% C</p> Signup and view all the answers

    Which alloying element affects the eutectoid composition of steel?

    <p>Ti</p> Signup and view all the answers

    What is the eutectoid temperature dependence on alloy concentration shown for in Fig. 9.35?

    <p>Carbon (C)</p> Signup and view all the answers

    In steel, what composition results in the formation of a mixture of pearlite and Fe3C?

    <p>0.512 wt% C</p> Signup and view all the answers

    What is the main difference between eutectic, eutectoid, and peritectic transformations?

    <p>Number of solid phases involved</p> Signup and view all the answers

    In the Fe-C phase diagram, what transformation is represented by the curve labeled 'B'?

    <p>Eutectoid</p> Signup and view all the answers

    What is the composition of the eutectic phase in the Pb-Sn system?

    <p>61.9 wt% Sn</p> Signup and view all the answers

    Which type of transformation involves a liquid and one solid phase transforming to a second solid phase?

    <p>Peritectic</p> Signup and view all the answers

    What is the result of the transformation represented by the curve labeled 'B' in the Fe-C phase diagram?

    <p>Pearlite formation</p> Signup and view all the answers

    What does the eutectoid transformation involve in the Fe-C system?

    <p>One solid phase transforming into two other solid phases</p> Signup and view all the answers

    What is the phase present at 1600°C for hypoeutectoid steel?

    <p>γ</p> Signup and view all the answers

    In hypoeutectoid steel, what is the composition of proeutectoid ferrite?

    <p>1.0 wt% C</p> Signup and view all the answers

    What is the phase present at 1148°C for hypereutectoid steel?

    <p>Fe3C</p> Signup and view all the answers

    Which element is most abundant in the microstructure at 600 μm for hypereutectoid steel?

    <p>Fe</p> Signup and view all the answers

    For hypoeutectoid steel, what does Wpearlite stand for?

    <p>Weight percentage of pearlite</p> Signup and view all the answers

    At what temperature does austenite (γ) start to transform into pearlite for hypoeutectoid steel?

    <p>727°C</p> Signup and view all the answers

    Study Notes

    Lamellar Eutectic Structure

    • In eutectic systems, the microstructure consists of alternating layers of two phases (α and β)
    • For alloys with 18.3 wt% Sn < C0 < 61.9 wt% Sn, the microstructure develops as follows:
      • Primary α phase particles and a eutectic microconstituent
      • At TE (eutectic temperature), α + β phases are present
      • Just below TE, α + β phases are present
      • Just above TE, β phase is present

    Hypoeutectic and Hypereutectic Alloys

    • Hypoeutectic alloys have a composition of C0 < 61.9 wt% Sn
    • Hypereutectic alloys have a composition of C0 > 61.9 wt% Sn
    • In hypoeutectic alloys, primary α phase particles and a eutectic microconstituent are present
    • In hypereutectic alloys, primary β phase particles and a eutectic microconstituent are present

    Eutectic, Eutectoid, and Peritectic Transformations

    • Eutectic transformation: L → α + β
    • Eutectoid transformation: S2 → S1 + S3
    • Peritectic transformation: L + S1 → S2
    • Examples of each type of transformation are given for Pb-Sn, Fe-C, and Cu-Zn systems

    Iron-Carbon (Fe-C) Phase Diagram

    • The Fe-C phase diagram shows the phases present at different temperatures and compositions
    • Pearlite is a microstructure composed of alternating layers of α and Fe3C phases
    • The amount of pearlite in 100 g of alloy can be calculated using the weight fraction of α phase

    Alloying with Other Elements

    • The eutectoid composition and temperature can change with the addition of alloying elements
    • The dependence of eutectoid composition and temperature on alloy concentration is shown for several alloying elements in steel
    • Examples of alloying elements include Ti, Mo, Si, W, Cr, Ni, and Mn

    Hypoeutectoid and Hypereutectoid Steels

    • Hypoeutectoid steels have a composition of C0 < 0.76 wt% C
    • Hypereutectoid steels have a composition of C0 > 0.76 wt% C
    • The microstructure of hypoeutectoid and hypereutectoid steels is composed of proeutectoid ferrite or cementite and pearlite
    • The amount of pearlite in 100 g of alloy can be calculated using the weight fraction of α phase

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    Test your knowledge on lamellar eutectic structures and microstructural developments in eutectic systems. Questions are based on Chapter 9 from the Metals Handbook, 9th edition, and Callister & Rethwisch 10th edition.

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