This set of Heat Treatment of Metals and Alloys Multiple Choice Questions & Answers (MCQs) focuses on “Steels – Pearlitic Transformation”.
1. Which one of the following statements is correct regarding pearlitic transformation?
a) At large undercooling, site saturation takes place along grain boundaries
b) At low undercooling, site saturation takes place along grain boundaries
c) At large undercooling, small number of nuclei are formed
d) Number of nuclei formed is independent of undercooling
View Answer
Explanation: At large undercooling, site saturation takes place along grain boundaries due to high nucleation rate. At small undercooling small number of nuclei are formed. The nuclei formed grow without any interference.
2. The microstructure of pearlite consists of alternate layers of ferrite and cementite.
a) True
b) False
View Answer
Explanation: Pearlite consists of alternate layers of ferrite and cementite. It has a lamellar structure. Pearlite is a very important constituent in steel.
3. Which one of the following statements is correct regarding formation of pearlite?
a) Pearlite is formed by cooling austenite of eutectoid composition just below upper critical temperature
b) Pearlite is formed by cooling austenite of eutectoid composition just below lower critical temperature
c) Pearlite is formed by cooling austenite of eutectic composition just below lower critical temperature
d) Pearlite is formed by cooling austenite of eutectic composition just below upper critical temperature
View Answer
Explanation: Pearlite is formed when austenite is cooled just below lower critical temperature. It is very important that the composition will be that of eutectoid i.e. 0.76% carbon in iron.
4. Pearlite formed at just below lower critical temperature has which one of the following composition?
a) 80% ferrite and 20% cementite
b) 88% ferrite and 12% cementite
c) 85% ferrite and 15% cementite
d) 90% ferrite and 10% cementite
View Answer
Explanation: The pearlite formed by cooling austenite at a temperature below lower critical temperature contains 88% ferrite and 12% cementite. Ferrite is a continuous phase in this case.
5. Which one of the following statements is correct regarding ferrite?
a) It is pure iron
b) It has very low carbon content
c) It has very high carbon content
d) The carbon content vary a lot
View Answer
Explanation: Sometimes it is said that ferrite is pure iron but it is not true. Ferrite contains very low carbon content. The carbon content is so low that we assume it to be pure iron for simpler calculations.
6. Pearlite transformation is a diffusion controlled process.
a) True
b) False
View Answer
Explanation: Pearlite transformation is diffusion controlled process. Martensitic transformation is a diffusionless process. The speed of martensite formation is so fast and it occurs at such a low temperature that diffusion is very tough to take place.
7. What are the active nuclei for austenite to bainite transformation?
a) Cementite crystals
b) Ferrite crystals
c) Austenite crystals
d) Epsilon carbide crystals
View Answer
Explanation: For any transformation, the nucleus which is first formed is referred to as active nuclei. In case of austenite to bainite transformation, they are ferrite crystals.
8. What are the active nuclei for pearlitic transformation?
a) Cementite platelets
b) Ferrite platelets
c) Austenite platelets
d) Epsilon carbide platelets
View Answer
Explanation: For any transformation, the nucleus which is first formed is referred to as active nuclei. In case of pearlitic transformation, they are cementite platelets.
Sanfoundry Global Education & Learning Series – Heat Treatment of Metals and Alloys.
To practice all areas of Heat Treatment of Metals and Alloys, here is complete set of Multiple Choice Questions and Answers.
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