4931_Grace College of Engineering_Thoothukudi
DEPARTMENT OF MECHANICAL ENGINEERING
BE- Mechanical Engineering
Anna University Regulation: 2021
ME3392 Engineering Materials and Metallurgy
II Year/III Semester
Question Bank
Unit- II Heat Treatment
Prepared By,
Dr M D Mohan Gift, Prof/MECH
ME3392_EMM
4931_Grace College of Engineering_Thoothukudi
Department of Mechanical Engineering
ME3392 EMM Question Bank
Unit 2: Heat Treatment
Part A – Two Mark Questions (20)
1. What is full annealing?
Full annealing is a heat treatment process that softens steel by heating it above its
critical temperature, holding it there, and then cooling it slowly in the furnace. This
treatment improves ductility and machinability while relieving internal stresses. It is
commonly used for preparing steel for machining and forming operations.
2. Define stress relief annealing.
Stress relief annealing reduces residual stresses in materials caused by welding,
casting, or machining. The material is heated below its recrystallization temperature
(500-650°C for steel) and cooled slowly to improve dimensional stability. This process
minimizes risks like warping and cracking during subsequent operations.
3. What is recrystallization annealing?
Recrystallization annealing restores the original grain structure of cold-worked
metals. The metal is heated above its recrystallization temperature (400-600°C for steel),
allowing new grains to form and reducing hardness. This process is used after cold
forming to regain ductility for further processing.
4. Explain spheroidizing.
Spheroidizing is a heat treatment for high-carbon steels that creates globular
carbides to improve machinability and ductility. The steel is heated just below its critical
temperature (~700°C) for an extended time, then cooled slowly. This process reduces
hardness and prepares steel for further shaping.
5. What is normalizing?
Normalizing refines the grain structure of steel by heating it above its critical
temperature, holding it, and cooling it in air. This process improves mechanical
properties like strength and toughness while relieving internal stresses. Normalizing is
often done after forging or casting.
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4931_Grace College of Engineering_Thoothukudi
6. What is the purpose of hardening?
Hardening increases the hardness and strength of steel by forming martensite, a
very hard microstructure. The steel is heated above its critical temperature, held, and then
rapidly quenched in water, oil, or air. This process is used for tools and machine parts
requiring wear resistance.
7. Define tempering.
Tempering reduces the brittleness of hardened steel while retaining its strength.
The steel is reheated below its critical temperature (150-650°C) and cooled slowly,
relieving internal stresses. This treatment improves toughness, making steel suitable for
tools and automotive parts.
8. Differentiate annealing and normalizing.
Annealing involves slow cooling in a furnace, producing a soft and ductile
structure, while normalizing cools steel in air, yielding higher strength and hardness.
Annealed steel is used for machining, while normalized steel is suitable for structural
components requiring toughness.
9. What is a TTT diagram?
A Time-Temperature-Transformation (TTT) diagram shows how the phases in
steel change with time at constant temperatures. It helps predict the formation of pearlite,
bainite, or martensite during heat treatment. TTT diagrams are essential for designing
precise heat treatment processes.
10. What is bainite?
Bainite is a microstructure formed when steel is cooled to an intermediate
temperature (250-550°C) and held. It consists of fine ferrite and cementite, offering a
combination of strength and toughness. Bainite is tougher than pearlite and used in
applications requiring durability.
11. What is martensite?
Martensite is a hard and brittle microstructure formed by rapidly quenching
austenite below 250°C. It provides high hardness and wear resistance but requires
tempering to improve toughness. Martensite is used in cutting tools and wear-resistant
machine parts.
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4931_Grace College of Engineering_Thoothukudi
12. Define austempering.
Austempering is a heat treatment process where steel is quenched to a
temperature just above where martensite forms and held until bainite develops. This
produces a tough and strong structure without brittleness. It is commonly used for gears
and springs.
13. What is martempering?
Martempering reduces the risk of cracking in steel by cooling it to a temperature
just above martensite formation, holding it briefly, and then cooling to room temperature.
This treatment forms martensite with less internal stress. It is used for tools and knives.
14. What is hardenability?
Hardenability is the ability of steel to harden deeply beneath its surface during
quenching. It depends on the chemical composition and cooling rate. Steels with high
hardenability are suitable for large components like gears and shafts.
15. Explain the Jominy end-quench test.
The Jominy test measures the hardenability of steel by quenching one end of a
heated steel sample with water and measuring hardness along its length. The hardness
profile indicates how deeply the steel can harden. This test helps engineers select suitable
steels for specific applications.
16. What is carburizing?
Carburizing hardens the surface of steel by heating it in a carbon-rich
environment and quenching. Carbon diffuses into the surface, making it wear-resistant
while keeping the core tough. This process is used for gears and shafts.
17. Define nitriding.
Nitriding involves heating steel in a nitrogen-rich environment to form a hard
surface layer. It occurs at lower temperatures than carburizing and does not require
quenching. Nitriding is used for engine parts like crankshafts and cams.
18. What is the purpose of flame hardening?
Flame hardening uses a high-temperature flame to heat the surface of steel,
followed by rapid cooling to form a hard layer. The core remains soft and tough. This
method is used for large gears and rails.
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4931_Grace College of Engineering_Thoothukudi
19. What is sintering?
Sintering is a process where powdered materials are pressed into a shape and
heated below the melting point to bond particles together. It produces high-strength and
precise components like gears and bearings. This method is efficient and reduces material
waste.
20. Explain thermo-mechanical treatment.
Thermo-mechanical treatment combines heating and mechanical deformation to
improve strength and ductility in metals. It includes forging, rolling, or pressing at
elevated temperatures. This treatment is used for structural components requiring
enhanced toughness.
Part B – 13 Mark Questions (15)
1. Explain the process and applications of full annealing.
2. Discuss the purpose and method of stress relief annealing.
3. Explain recrystallization annealing with its industrial applications.
4. Describe spheroidizing and its role in machining high-carbon steels.
5. Compare annealing, normalizing, and hardening processes.
6. Explain the formation of martensite, bainite, and pearlite using a TTT diagram.
7. Discuss austempering and martempering, highlighting their differences.
8. Explain the Jominy end-quench test and its significance in evaluating steel hardenability.
9. What are carburizing and nitriding? Explain their processes and applications.
10. Discuss the differences between flame hardening and induction hardening.
11. Explain the significance of CCT diagrams in designing heat treatment processes.
12. Describe thermo-mechanical treatments and their effects on material properties.
13. Explain the process of sintering and its advantages over traditional manufacturing.
14. Discuss vacuum and plasma hardening, highlighting their advantages and applications.
15. Compare case hardening techniques like carburizing, nitriding, and cyaniding.
ME3392_EMM