This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Normalising, Quenching”.
1. How is cooling of the material done is normalising process?
b) Cooling tower
c) Still air
d) Liquid chamber
Explanation: Normalising is a process similar to annealing, which helps to refine grain structure, increase strength, and relieve stresses and other properties. Cooling for annealing is done in a furnace, whereas it is done in still air for normalising.
2. Normalising is best used for is which kind of materials?
a) Steel castings
b) Steel wires
c) High carbon steels
d) Low and medium carbon steels
Explanation: Normalising is a process similar to annealing, where the material is subjected to temperature changes to alter their properties. This process is particularly employed for low and medium carbon steels, as well as alloy steels.
3. For normalising, the steel is heated ___________ its upper critical temperature.
a) 30-40oC above
b) 30-40oC C below
c) 50-60oC C above
d) 50-60oC C below
Explanation: For hypoeutectoid steels, normalising is done by heating the steel 50-60oC C above its upper critical temperature (A3 line). For hypereutectoid steels, it is heated above the Acm line. The steel is held at that temperature for some time and then allowed to cool in still air.
4. Which of the following is not applicable for normalising process?
c) Fine grain structure
d) Variable properties
Explanation: Normalising is carried out by heating of the steel at higher temperatures (compared to annealing) and then cooling it in still air. Since cooling is different at different locations, their properties will also vary. It also provides a fine grain structure and is less time-consuming.
5. The structure obtained by normalising depends on __________
a) Stresses induced
b) Toughness of material
c) Thickness of cross section
d) Strength of weld
Explanation: The type of structure obtained by normalising largely depends on the thickness of the cross-section of the material, as this also affects the rate of cooling. Thin sections tend to give a finer grain structure than thick sections.
6. Microstructure containing ferrite is termed as _________
a) Dark area
b) White network
c) Red area
d) Blue zone
Explanation: Normalising produces microstructure containing ferrite (white network) and pearlite (dark area) for hypoeutectoid steels. For eutectoid steels, the microstructure is only pearlite. Meanwhile, for hypereutectoid steels, it is a pearlite and cementite microstructure.
7. Which among the following media of quenching the slowest?
a) Caustic soda
b) Sodium chloride
c) Mineral oil
Explanation: The rate of cooling heavily depends on the quenching medium used. 5-10% caustic soda and 5-20% NaCl are the two most popular media in terms of severity, followed by cold and warm water. This is followed by mineral, animal, and vegetable oils. Finally, air has the lowest severity of the preferred media.
8. Which of the following is not a preferred vegetable oil for quenching medium?
Explanation: Oils are generally more effective as quenching media as compared to air. In decreasing order, mineral oil, animal oil, and vegetable oil are widely used. The commonly used vegetable oils are linseed, cottonseed, and rapeseed.
9. Mineral oils are used in the hardening process of ____________
c) Alloy steel
d) Heavy forging
Explanation: Mineral oils are obtained during the refining of crude petroleum. These are widely used as quenching media due to their severity of quench. Mineral oils are used in hardening alloy steels.
10. Which quenching medium is used for quenching of carbon and low alloy steels?
a) Vegetable oil
d) Animal oil
Explanation: Water produces the most severe quench followed by oils and air. For the quenching of carbon and low alloy steels, water or an aqueous solution of NaOH or NaCl is used.
11. Which stage of quenching is the slowest?
b) Vapour-Transport cooling
d) They are all equally slow
Explanation: In general, both vapor-jacket and liquid-cooling are slow cooking stages. However, liquid-cooling is the slowest as all the heat transfer occurs through conduction across the solid-liquid interface.
12. Vapour-jacket cooling stage of quenching process occurs _________
a) Below boiling point
b) Above boiling point
c) Below melting point
d) At recrystallization temperature
Explanation: The vapor-jacket stage of quenching is a slow cooling stage since all the heat is transported through a gas by conduction and radiation. This stage occurs when the metal is above the boiling point of the quenchant.
Sanfoundry Global Education & Learning Series – Engineering Materials & Metallurgy.
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