1. Which heat treatment process involves heating a metal above its critical temperature, followed by rapid quenching to achieve high hardness and strength?
a) Annealing
b) Normalizing
c) Martensite transformation
d) Spheroidizing
Answer: c) Martensite transformation
Explanation: Martensite transformation involves rapid cooling of austenite to form a supersaturated solid solution, resulting in high hardness and strength in the metal.
2. What surface heat treatment method involves introducing carbon into the surface layer of a metal to increase its hardness?
a) Nitriding
b) Spheroidizing
c) Austenitizing
d) Tempering
Answer: a) Nitriding
Explanation: Nitriding involves the diffusion of nitrogen into the surface layer of a metal to form hard nitrides, increasing surface hardness and wear resistance.
3. Which type of annealing process involves heating a metal to a temperature below its critical range and then slowly cooling it in the furnace?
a) Full annealing
b) Isothermal annealing
c) Process annealing
d) Stress-relief annealing
Answer: a) Full annealing
Explanation: Full annealing involves heating the metal to a temperature slightly above its critical range and then slowly cooling it in the furnace, allowing for complete softening and homogenization of the metal structure.
4. In which phase transformation does austenite transform into a mixture of ferrite and cementite in the microstructure of steel?
a) Pearlite
b) Bainite
c) Martensite
d) Troostite
Answer: a) Pearlite
Explanation: Pearlite is a phase transformation in steel where austenite transforms into a lamellar structure consisting of alternate layers of ferrite and cementite.
5. Which heat treatment method involves heating a metal to a temperature below its critical range, holding it at that temperature for a period, and then cooling it in still air?
a) Normalizing
b) Annealing
c) Tempering
d) Martensite transformation
Answer: c) Tempering
Explanation: Tempering involves reheating hardened or normalized steel to a temperature below the critical range, holding it for a specific time, and then cooling it in still air to reduce brittleness and increase toughness.
6. What type of microscope is commonly used for metallographic studies to examine the microstructure of metals at high magnification?
a) Optical microscope
b) Electron microscope
c) X-ray microscope
d) Scanning probe microscope
Answer: b) Electron microscope
Explanation: Electron microscopes, such as scanning electron microscopes (SEM) and transmission electron microscopes (TEM), are commonly used for metallographic studies due to their high magnification and resolution capabilities.
7. Which heat treatment process involves heating a metal to a temperature above its critical range and then cooling it in still air to achieve a refined grain structure and improved mechanical properties?
a) Normalizing
b) Annealing
c) Quenching
d) Martensite transformation
Answer: a) Normalizing
Explanation: Normalizing involves heating a metal to a temperature above its critical range, holding it at that temperature for a period, and then cooling it in still air to refine the grain structure and improve mechanical properties.
8. Which surface hardening method involves heating a metal surface with a laser beam and then rapidly quenching it to achieve hardened surface layers?
a) Carburizing
b) Cyaniding
c) Laser hardening
d) Boriding
Answer: c) Laser hardening
Explanation: Laser hardening is a surface hardening method that involves heating the metal surface with a laser beam and then rapidly quenching it to achieve hardened surface layers with minimal distortion of the base material.
9. What is the purpose of spheroidizing heat treatment?
a) To increase hardness
b) To improve machinability
c) To reduce brittleness
d) To refine grain structure
Answer: b) To improve machinability
Explanation: Spheroidizing heat treatment is performed to improve the machinability of steels by converting cementite into spheroidized carbides, which reduces tool wear during machining.
10. Which phase transformation involves the decomposition of austenite into fine lamellae of ferrite and cementite in steel?
a) Bainite
b) Troostite
c) Martensite
d) Pearlite
Answer: a) Bainite
Explanation: Bainite is a phase transformation in steel where austenite decomposes into fine lamellae of ferrite and cementite, resulting in a microstructure that provides a balance of strength and ductility.
11. Which heat treatment method is used to relieve internal stresses in a metal without significantly affecting its microstructure?
a) Annealing
b) Tempering
c) Stress-relief annealing
d) Martensite transformation
Answer: c) Stress-relief annealing
Explanation: Stress-relief annealing involves heating a metal to a temperature below its critical range and holding it at that temperature to relieve internal stresses, without significantly altering its microstructure.
12. What is the purpose of boriding as a surface heat treatment method?
a) To increase electrical conductivity
b) To improve corrosion resistance
c) To enhance wear resistance
d) To reduce surface roughness
Answer: c) To enhance wear resistance
Explanation: Boriding is a surface heat treatment method that involves diffusing boron into the surface of a metal to form hard boride layers, increasing wear resistance and surface hardness.
13. Which heat treatment process involves heating a metal to a temperature above its upper critical temperature and then cooling it rapidly in a quenching medium such as water or oil?
a) Annealing
b) Normalizing
c) Tempering
d) Quenching
Answer: d) Quenching
Explanation: Quenching involves heating a metal to a temperature above its upper critical temperature and then rapidly cooling it in a quenching medium to achieve high hardness and strength.
14. What is the primary purpose of case carburizing as a surface heat treatment method?
a) To improve ductility
b) To increase hardness at the surface
c) To reduce surface roughness
d) To enhance thermal conductivity
Answer: b) To increase hardness at the surface
Explanation: Case carburizing involves introducing carbon into the surface layer of a metal to increase its hardness, wear resistance, and fatigue strength at the surface.
15. Which heat treatment process involves heating a metal to a temperature above its critical range and then slowly cooling it in the furnace to produce a refined grain structure and improve machinability?
a) Full annealing
b) Isothermal annealing
c) Process annealing
d) Spheroidizing
Answer: a) Full annealing
Explanation: Full annealing involves heating a metal to a temperature above its critical range and then slowly cooling it in the furnace, resulting in a refined grain structure and improved machinability.