This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Annealing – 1”.
1. Which of the following factors does not influence the variety and quality of metal?
a) Rate of heating and cooling
b) Quenching medium
d) Grain size
Explanation: The variety of metal and various metallurgical processes depend upon the method and rate of heating and cooling, furnaces used, and quenching medium. Grain size is one of the effects of heat treatment, not a cause for any change.
2. How does the rate of cooling affect the hardness of the metal?
a) Slow cooling, hard material
b) Slow cooking, soft material
c) Rapid cooling, soft material
d) No effective change
Explanation: The rate of cooling is the controlling factor in developing either a hard or soft structure. Rapid cooling from critical range results in a hard structure, whereas very slow cooling gives a soft structure.
3. Which of the following is not a stage of annealing?
Explanation: Annealing is defined as the softening process which involves heating the material at an elevated temperature and then slowly cooling it. The annealing cycle consists of three stages of heating to the desired temperature, holding at that temperature (soaking), and then slowly cooling (quenching).
4. Full annealing is applied to which kind of materials?
a) Steel castings
b) Steel wires
c) High carbon steels
d) Sheet products
Explanation: When we refer to annealing, usually we only talk about full annealing. This method is used to soften the material, to refine crystalline structure, and relieve stresses. This method is applied to steel castings and steel ingots.
5. For full annealing of hypoeutectoid steels, they are heated in a range above __________
Explanation: Hypoeutectoid steels contain carbon content which is less than 0.77%. For full annealing of this steel, it is heated 30-60oC above the A3 line. It is held at this temperature for a period of time, and then slowly cooled to room temperature.
6. Cooling of hypoeutectoid steels in done is furnace by decreasing the temperature to at least ________ below the A1 line.
Explanation: For full annealing of this steel, it is heated 30-60oC above the A3 line. Then it is cooled within the furnace by decreasing the temperature 10-30oC per hour, to at least 30oC below A1 line.
7. What is the result of full annealing of hypoeutectoid steels?
a) Coarse pearlite
Explanation: Hypoeutectoid steels are heated above the A3 line and then cooled in the furnace. Then it removed from the furnace and then cooled at room temperature. This results in coarse pearlite with excess ferrite.
8. How does heating for hypereutectoid steels differ from hypoeutectoid steels?
a) Heated 30-60oC above A1 line
b) Heated 30-60oC below A1 line
c) Heated 30-60oC below A2 line
d) Heated 30-60oC below A3 line
Explanation: Hypoeutectoid steels are heated above the A3 line and then cooled in the furnace. On the other hand, hypereutectoid steels are heated 30-60oC above the A1 line and then cooled similar to hypoeutectoid steels.
9. Heating of hypereutectoid steels results in formation of coarse pearlite with excess __________
Explanation: Similar to hypoeutectoid steels, hypereutectoid steels are heated 30-60oC above the A1 line. This results in coarse pearlite with excess cementite in a dispersed spheroidal form. This improves mechanical properties, ductility, and toughness.
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