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?

18.3% (D) 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?

0.27% (A) Signup and view all the answers

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

$200 °C$ (B) Signup and view all the answers

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

727°C (C) Signup and view all the answers

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

Fe3C (B) Signup and view all the answers

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

1148°C (D) Signup and view all the answers

Which phase is predominantly present in hypoeutectoid steel?

α (C) Signup and view all the answers

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

6.7% (C) Signup and view all the answers

What is the amount of pearlite in 200 g?

105.6 g (D) Signup and view all the answers

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

727°C (D) Signup and view all the answers

What is the weight percentage of carbon in cementite?

0.40 wt% C (D) Signup and view all the answers

Which alloying element affects the eutectoid composition of steel?

Ti (B) Signup and view all the answers

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

Carbon (C) (B) Signup and view all the answers

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

0.512 wt% C (C) Signup and view all the answers

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

Number of solid phases involved (A) Signup and view all the answers

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

Eutectoid (D) Signup and view all the answers

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

61.9 wt% Sn (C) Signup and view all the answers

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

Peritectic (C) 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?

Pearlite formation (C) Signup and view all the answers

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

One solid phase transforming into two other solid phases (D) Signup and view all the answers

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

γ (D) Signup and view all the answers

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

1.0 wt% C (A) Signup and view all the answers

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

Fe3C (D) Signup and view all the answers

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

Fe (B) Signup and view all the answers

For hypoeutectoid steel, what does Wpearlite stand for?

Weight percentage of pearlite (D) Signup and view all the answers

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

727°C (A) Signup and view all the answers

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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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