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Questions and Answers
In the Pb-Sn system, which phase is present just below the eutectic temperature (TE)?
For alloys with a composition of 97.8 wt% Sn, what is the microconstituent present just above TE?
What weight percentage of Sn is required for hypoeutectic alloys in the Pb-Sn system?
What is the weight percentage of Sn for alloys that exhibit primary α eutectic in the Pb-Sn system?
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In the microstructure of alloys with a composition of 97.8 wt% Sn, what is the weight percentage of the β phase?
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At what temperature do α and β phases coexist in the Pb-Sn system?
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What is the eutectoid temperature for the Fe-C system?
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Which phase is described as 'cementite-hard' in the Fe-C system?
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At what temperature does proeutectoid ferrite form in the Fe-C system?
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Which phase is predominantly present in hypoeutectoid steel?
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What is the carbon content, in weight percent, of eutectic composition in the Fe-C system?
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What is the amount of pearlite in 200 g?
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At what temperature does austenite transform into a mixture of austenite and ferrite?
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What is the weight percentage of carbon in cementite?
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Which alloying element affects the eutectoid composition of steel?
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What is the eutectoid temperature dependence on alloy concentration shown for in Fig. 9.35?
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In steel, what composition results in the formation of a mixture of pearlite and Fe3C?
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What is the main difference between eutectic, eutectoid, and peritectic transformations?
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In the Fe-C phase diagram, what transformation is represented by the curve labeled 'B'?
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What is the composition of the eutectic phase in the Pb-Sn system?
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Which type of transformation involves a liquid and one solid phase transforming to a second solid phase?
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What is the result of the transformation represented by the curve labeled 'B' in the Fe-C phase diagram?
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What does the eutectoid transformation involve in the Fe-C system?
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What is the phase present at 1600°C for hypoeutectoid steel?
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In hypoeutectoid steel, what is the composition of proeutectoid ferrite?
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What is the phase present at 1148°C for hypereutectoid steel?
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Which element is most abundant in the microstructure at 600 μm for hypereutectoid steel?
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For hypoeutectoid steel, what does Wpearlite stand for?
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At what temperature does austenite (γ) start to transform into pearlite for hypoeutectoid steel?
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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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Description
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.
