Manufacturing Processes Multiple Choice Questions on “Quenching”.
1. Quenching is the process of _______
a) rapid cooling
b) slow cooling
c) rapid heating
d) slow heating
Answer: a
Clarification: Quenching is the process of rapidly cooling material from high temperature. This rapid cooling is achieved using quenching media. Quenching is done during the hardening process.
2. Quenching medium is decided on the basis of ______
a) weight of the specimen
b) material of the specimen
c) thickness of the specimen
d) application of the specimen
Answer: c
Clarification: The thickness of the material to be quenched along with the rate of cooling required helps to choose the quenching medium. The quenching medium has to be chosen carefully.
3. How many types of quenching are there?
a) 2
b) 3
c) 4
d) 5
Answer: b
Clarification: There are many different types of quenching:
• quenching in a fine vapour or mist is known as fog quenching
• if quenching is carried out directly from some other heat treatment operation (carburizing for example), it is known as direct quenching
• if only some portions of a workpiece are quenched, it is known as selective quenching.
4. An alloy quenched past the nose of the C-curve in the isothermal transformation diagram will undergo _______ transformation.
a) martensitic
b) perlitic
c) austentic
d) ferritic
Answer: a
Clarification: The most common example of quenching is what is used in steels; an alloy quenched past the nose of the C-curve in the isothermal transformation diagram will undergo a martensitic transformation, which will lead to high hardness in the material.
5. Quenching is can also be used for _____
a) fibres
b) polymers
c) metallic glasses
d) plastics
Answer: c
Clarification: Quenching can also be possible to rapidly quench molten metallic liquids to retain the liquid-like structure; such materials are commonly known as metallic glasses. Quenching is also a method used to determine hardenability of materials.
6. Quenching is generally carried out to _____
a) remove brittleness
b) remove rust
c) freeze the high temperature structure
d) oxidise the surface of the component for good reason
Answer: c
Clarification: Quenching is generally carried out to freeze the high temperature structure or phase in the material; however, it is not always possible for the structure to be retained.
7. The heat transfer during quenching is related to heat transfer during ______
a) annealing
b) boiling
c) martempering
d) hardening
Answer: b
Clarification: The heat transfer during quenching is very closely related to heat transfer during boiling; and, boiling is a very complicated phenomenon as far as the energy transport is considered.
8. If a quenching medium cools slower than the required rate, the final product will have different properties than desired.
a) True
b) False
Answer: a
Clarification: If a quenching medium that cools slower than the required rate is chosen, the quench is not effective in producing the required microstructures and hence properties.
9. If the quenching medium cools the specimen at a faster rate, cracks might occur in the specimen.
a) True
b) False
Answer: a
Clarification: If a quenching medium that cools faster than the required rate is used, then that can sometimes lead to defects such as warping and cracking. Therefore special care should be taken while selecting the quenching medium.
10. During quenching, there could be a mechanism like ______
a) vacancy diffusion
b) vacancy formation
c) grain diffusion
d) grain boundary distortion
Answer: a
Clarification: During quenching, there could be mechanisms such as vacancies diffusing to the grain boundaries leading to PFZs (Precipitate Free Zones) that become operative.