This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Tempering”.
1. Which of the following is not a result of tempering?
a) Increased ductility
b) Improved toughness
c) Increased electrical conductivity
d) Internal stresses are relieved
View Answer
Explanation: Martensite formed during the hardening process is too brittle and lacks toughness and ductility. This makes it unusable for many applications. Therefore, a heat treatment process called tempering is done to bring about these changes.
2. Tempering of martensite steel is done _________
a) Below eutectic temperature
b) Below eutectoid transformation temperature
c) At room temperature
d) At 1000oC
View Answer
Explanation: Tempering is a process of heating martensite steel below the eutectoid transformation temperature (250-650oC). It is held there for some time and slowly cooled to room temperature.
3. Internal stresses in martensite steel are relieved by heating at __________
a) 200oC
b) 500oC
c) 800oC
d) 1000oC
View Answer
Explanation: Tempering usually involves heating the martensite steel below the eutectoid transformation temperature (250-650oC). When this martensite steel is heated at temperatures as low as 200oC, internal stresses are relieved.
4. What kind of transformation occurs during tempering of martensite steel?
a) BCC to FCC
b) BCT to HCP
c) FCC to BCT
d) BCT to α+Fe3C
View Answer
Explanation: Tempering is a process of heating martensite steel below the eutectoid transformation temperature. This heat treatment process transforms martensite (BCT, single phase) into tempered martensite (α+Fe3C) by the diffusional process.
5. How is the tensile strength of the material affected due to tempering?
a) Increases with an increase in temperature
b) Decreases with an increase in temperature
c) Increases constantly
d) Does not change
View Answer
Explanation: We know that hardness of the material decreases with an increase in tempering time. Similarly, the tensile and yield strengths of the material also decrease with increase in tempering temperature.
6. How is the ductility of the material affected due to tempering?
a) Increases with an increase in temperature
b) Decreases with an increase in temperature
c) Increases constantly
d) Does not change
View Answer
Explanation: The hardness and tensile and yield strengths of the material decrease with increasing tempering temperature. On the other hand, however, it is noted that the ductility of the material increases with an increase in tempering temperature.
7. Low temperature tempering occurs at __________
a) 50-150oC
b) 150-250oC
c) 350-450oC
d) 500-650oC
View Answer
Explanation: Tempering temperature is classified into three classes. Low temperature tempering occurs at 150-250oC. Medium and high temperature tempering occur at 350-450oC and 500-650oC correspondingly.
8. Medium temperature tempering develops a ________ structure.
a) Non-lamellar
b) Sorbite
c) Tempered-troostite
d) Bainite
View Answer
Explanation: Medium temperature tempering is usually carried out in a temperature range between 350oC and 450oC. This process develops a tempered-troostite structure.
9. Tempering that results in a reduction of toughness is known as __________
a) Caustic embrittlement
b) Temper embrittlement
c) End-temper
d) Quench-temper embrittlement
View Answer
Explanation: Tempering of some steels and alloys may result in the reduction of toughness. This phenomenon is known as temper embrittlement.
10. High temperature tempering develops a ________ structure.
a) Non-lamellar
b) Sorbite
c) Tempered-troostite
d) Pearlite
View Answer
Explanation: High-temperature tempering is usually carried out in a temperature range between 500oC and 650oC. This process develops a sorbite structure. This is used to completely eliminate internal stresses in the material.
11. Temper embrittlement occurs at a temperature __________
a) Below 0oC
b) Above 250oC
c) Above 575oC
d) Above 1000oC
View Answer
Explanation: Tempering of some steels and alloys may result in the reduction of toughness. This phenomenon is known as temper embrittlement. Temper embrittlement occurs when the steel is tempered above 575oC which is followed by slow cooling to room temperature.
12. Which tempering process is used to increase the endurance and elastic limit of the material?
a) Low-temperature tempering
b) Medium temperature tempering
c) High-temperature tempering
d) Endurance limit cannot be increased
View Answer
Explanation: Medium temperature tempering is performed between 350oC and 450oC. This process develops a tempered-troostite structure and increases the endurance and elastic limits of the material.
13. What are the applications of medium temperature tempering?
a) Spring and die steels
b) Structural steels
c) Low alloy steels
d) Surface hardened regions
View Answer
Explanation: Medium temperature tempering is applied on materials like spring steels and die steels. Likewise, high-temperature tempering is used on structural steels. Low-temperature tempering is applied to cutting and measuring tools of carbon and low alloy steels, as well as for surface-hardened and case-carburized parts.
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