Manufacturing Processes Questions and Answers – Annealing – 3

This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Annealing – 3”.

1. The rate of recrystallization can be enhanced by ______
a) increasing the temperature
b) increasing the percentage of cold work
c) increasing the rate of cooling
d) applying pressure

Answer: b
Explanation: Increasing the percentage of cold work enhances the rate of recrystallization, with the result that the recrystallization temperature is lowered, and approaches a constant or limiting value at high deformations.

2. The critical degree of cold work lies between _____ of cold work.
a) 2% and 20%
b) 5% and 10%
c) 7% and 15%
d) 20% and 30%

Answer: a
Explanation: There exists some critical degree of cold work below which recrystallization cannot be made to occur; normally, this is between 2% and 20% cold work.

3. The recrystallization in pure metal is faster than in _____
a) non-metals
b) alloys
c) polymers
d) d-block metals

Answer: b
Explanation: Recrystallization proceeds more rapidly in pure metals than in alloys. It is believed that impurity atoms preferentially segregate at and interact with these recrystallized grain boundaries so as to diminish their mobilities; this results in a decrease of the recrystallization rate and raises the recrystallization temperatures.

4. For pure metals, the recrystallization temperature is normally _____
a) equal to Tm
b) 0.5 Tm
c) 0.8 Tm
d) 0.3 Tm

Answer: d
Explanation: For pure metals, the recrystallization temperature is normally 0.3 Tm, where Tm is the absolute temperature; for some commercial alloys it may run as high as 0.7 Tm.

5. In hot working, plastic deformation operations are often carried out at temperatures above the ______ temperature.
a) melting
b) recrystallization
c) room
d) cold working

Answer: b
Explanation: Plastic deformation operations are often carried out at temperatures above the recrystallization temperature in a process termed hot working. The material remains relatively soft and ductile during deformation because it does not strain harden, and thus large deformations are possible.

6. Which of the following metals has recrystallization temperature below 0⁰C?
a) Pb
b) Zn
c) Al
d) Cu

Answer: a
Explanation: Recrystallization temperatures of these metals are as follows,
• Pb: -4⁰C
• Zn: 10⁰C
• Al: 80⁰C
• Cu: 120⁰C.

7. Which of the following metals has recrystallization temperature above 1000⁰C?
a) Cu- Zn alloy
b) Ni
c) Fe
d) W

Answer: d
Explanation: Recrystallization temperatures of these metals are as follows,
• Cu- Zn alloy: 475⁰C
• Ni: 370⁰C
• Fe: 450⁰C
• W: 1200⁰C.

8. Cold working increases ______ of the metal.
a) hardness
b) ductility
c) melting point
d) conductivity

Answer: a
Explanation: Cold working increases strength, hardness, and electrical resistance, and it decreases ductility. In the recovery stage of annealing, the physical and mechanical properties that suffered changes as a result of cold working tend to recover their original values.

9. Yield strength is the stress corresponding to point of intersection of stress-strain curve and strain offset line.
a) True
b) False

Answer: a
Explanation: A convention has been established wherein a straight line is constructed parallel to the elastic portion of the stress-strain curve at some specified strain offset, usually 0.002. The stress corresponding to the intersection of this line and the stress-strain curve as it bends over in the plastic region is defined as the yield strength.

10. The stress level at which plastic deformation begins is known as the proportional limit point.
a) True
b) False

Answer: b
Explanation: The stress level at which plastic deformation begins is known as yield point. For metals that experience this gradual elastic-plastic transition, the point of yielding may be determined as the initial departure from linearity of the stress-strain curve, as indicated by point P on the stress-strain curve and it is known as proportional limit.

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