unit-2 2marks questions

8/13/2019 UNIT-2 2marks Questions

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UNIT -II

HEAT TREATMENT

2 marks Question and Answers

1. Define the heat treatment?Heat treatment may be defined as an operation (or) Combination of operations involving heating

and cooling of a metal / alloy in solid state to obtain desirable properties.

2. What is the purposes of the processing heat treatments?a. To relieve internal stresses b. to refine the grain size c. to soften the metal,

d. To improve machinability. e. To improve hardness of the metal surface.

f. To improve mechanical properties like tensile strength, hardness, ductility, shock resistance etc

3. What is meant by annealing?Annealing is defined as a softening process consisting of heating the steel to a temperature at (or)

near the critical point, holding there for a proper time and then allowing it to cool slowly in

furnace.

4. What are the purposes of annealing?a. To relieve internal stresses. b. To induce softness. c. To refine grain structure.

d. To remove gases. e. To produce a definite microstructure.

f. To alter (or) improve properties like ductility, toughness, electrical, mechanical (or) other.

5. List the various stages of a heat treatment process.Stage 1: Heating a metal / alloy beyond the critical temperature.

Stage 2: Holding at that temperature for sufficient time period to allow necessary changes to

occur.

Stage 3:Cooling the metal / alloy (Quenching) at a rate necessary to obtain the desired propertie

6. List some of the heat treatment operations widely used.1. Annealing 2. Normalizing 3. Hardening 4. Tempering

5. Martempering 6. Austempering 7. Case Hardening.

7. List the different types of annealing?1. Full annealing. 2. Process annealing. 3. Stress relief annealing.

4. Spheroidizing annealing. 5. Recrystallisation annealing.

8. What is Quenching? List some of the quenching medium generally used in industries.Quenching means Rapid (or) fast cooling.

In industries 5 10% caustic soda, 5 20% brine (Nacl), cold water, warm water, animal o

mineral oil (obtained during the refining of crude petroleum), vegetable oil (cottonseed, linseed).


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9. What is meant by normalizing?It is similar to full annealing, but cooling is done in air instead of in the furnace.

10.Differentiate between normalizing and full annealing?S. No Normalizing Full Annealing

1 Normalizing is more economical than full

annealing (no furnace is required to control the

cooling rate)

Full annealing is Costly

2 Normalizing is less time consuming process Full annealing is more time

consuming process.

3 Normalizing temperature is higher than full

annealing.

Annealing temperature is lower

than that of normalizing

temperature.

4 It provides a fine grain structure. It provides coarse grain structure.

11.What are the factors should be considered while selecting a quenching medium.1. Desired rate of heat removal. 5. Stability under repeated use.

2. Required temperature interval. 6. Boiling point.

3. Flash point (If combustible). 7. Viscosity.

4. Possible reactions with the material being quenched. 8. Cost.

12.What are the three stages for quenching?Stage 1:Vapour-Jacket stage.

Stage 2:Vapour-transport cooling rate.

Stage 3:Liquid cooling rate.

13.What does the term hardening refer? What are the factors affecting the hardness .Hardening: It refers to the heat treatment of steel which increases its hardness by quenching.

Hardness obtained from the hardening process depends upon the following factors:

i. Carbon content ii. Quenching medium iii. Specimen size. iv. Other factors

14.Rate the order, effectiveness of the following quench media: oil, brine, water and molten saltMolten salt, Brine, water, and oil.

15.What is the benefit of Jominy end-quench test?For determining the hardenability of a given material.

16.What do you mean by embrittlement?The tempering of some steels / steel alloys may result in a reduction of toughness (increase in

brittleness). This phenomenon is referred as temper embrittlement.


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17.Distinguish the work hardening with the age hardening process.Work Hardening

1. It is also called as strain hardening,

2. It is the process of hardening a metal, whileworking on it (under cold working conditions)

Age Hardening

1. It is also called as Precipitation hardening.

2. It is the process of hardening a metal whenallowed to remain or age after heat treatment.

18.List some of the surface hardening techniques employed for altering surface chemistry.Diffusion methods

1.Carburizing

2. Nitriding

3. Cyaniding

4. Carbonitriding

Thermal methods

1. Flame hardening

2. Induction hardening

19.What are the differences between surface hardening by diffusion hardening methods andthermal methods?

Diffusion surface hardening process Thermal method of surface hardening

The hardness of the surface is improved by

diffusing interstitial elements like carbon,

Nitrogen, (or) both into the surface of steel

components.

Here only the surface of the steel components a

heated to above upper critical temperature an

suddenly quenched to get martensite formation o

the surface which gives higher hardness of th

surface.

20.What do you mean by the term case hardening?The term case hardening refers to the component or specimen surface should have high hardness.

In many applications, it (case hardening) is desirable.

While inside (or) core will be soft. This treatment is given to steel to achieve this

(hardness) are called as surface heat treatment or Case hardening.

21.What is Austempering and Martempering?Austempering

It is also called as Marquenching, Its an

interrupted cooling procedure used for steels to

minimize the stresses, distortion and cracking of

steels that may develop during rapid (or) fast

quenching.

Martempering

It is an isothermal heat treatment proces

usually used to reduce quenching distortio

and to make tough and strong steels.

22.What are some selective heating techniques employed for surface hardening?1. Flame hardening and 2. Induction hardening.

23.What is meant by selective hardening technique?It is a technique by which different properties are obtained simply by varying the thermal historieof the various regions.


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24.What are hardenability curves? What are the uses of them?The hardness curves are obtained from the data of Rockwell C hardness readings taken along the

length and the distance from the quenched end.

The practical use of end-quench hardenability curves are as follows:

1. If the quench rate (or) cooling rate for a given part is known, the Jominy hardenability curvescan predict the hardness of the part.

2. If the hardness at any point can be measured, the cooling rate at that point may be obtained fro

the hardenability curve for the material.

25.What is the difference between hardness and hardenability?Hardness is the property of a material by virtue of which it is able to resist abrasio

indentation and scratching. It is the mechanical property related to strength and is a strong functio

of carbon content of a metal.

Hardenability is the susceptibility of a material to get hardened. It is affected by the

alloying elements in the material and grain size.

26.What is meant by hardenability? What are the factors affecting it?Hardenability is a measure of ease of forming martensite.

Factors affecting the hardenability are:

(i) Composition of the steel.

(ii) Structure of the steel before quenching.

(iii) Austenite grain size.

(iv) Quenching medium and the method of quenching.

27.Why the tempering process usually follows hardening process justify.The martensite which is formed during the hardening process is too brittle and lacks good ductili

and toughness. Hence, it cannot be used for most applications.

The internal residual stresses that are introduced during hardening have a weakenin

effect. The ductility and toughness of martensite can be enhanced and those internal stresses ar

relieved by a heat treatment process known as tempering.

28.What is a TTT diagram?The TTT diagram is a plot of temperature versus the logarithm of time for a steel alloy of definite

composition. It is a tool used by heat treaters to predict quenching reactions in steels.

29.What is the significance of TTT diagram in the heat treatment of steel?TTTdiagram is most useful in giving an overall picture of the transformation behaviour of

austenite. This gives metallurgist to interpret the response of a steel to any specified heat

treatment.


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30.Why are TTT diagrams usually not applicable to industrial engineering practices?The data for the construction of TTT diagrams are obtained from the isothermal transformation o

austenite at differing temperatures. But most industrial heat treatments involve continuous coolin

from the austenitic temperature to room temperature. Thus a TTT diagram may not give a full

accurate representation of the temperatures and times of the transformations occurring.31.What is a CCT diagram?

The CCT diagram is a plot of temperature versus the logarithm of time for a steel alloy of definit

composition. It is used to indicate when transformations occur as the initially austenitised materi

is continuously cooled at a specific rate. In addition, it is also used to predict the fin

microstructure and mechanical characteristics.

32.Define the term Critical cooling rate (CCR). What are the factors affecting it?The slowest cooling rate of austenite that will result in 100% martensite formation is called

CCR. Factors affecting the critical cooling rate are:

(i) Chemical composition (ii) Hardening temperature (iii) Metallurgical nature (Purity) of steel.

33.What is the significance of Critical cooling rate (CCR)?It is the most important in hardening. In order to obtain a 100% martensitic structure on hardenin

the cooling must be much bigger than the critical cooling rate.

34.What is the effect of (a) tempering temperature, (b) tempering time on the hardness of steels(a) The Hardness gradually decreases as the temperature increases.

(b) The Hardness decreases with the increase in tempering time.

35.Differentiate between pack carburizing and gas carburizing?In Pack Carburizing, the components to be treated are packed into steel boxes, along with the

carburizing mixture, so that a space of roughly 50mm exists between them.

Gas carburizing, overcomes the drawbacks / difficulties of pack carburizing by replacing the

solid carburizing mixture with a carbon-providing gas.

36.In what way flame hardening differs from induction hardening?The mechanism and the purpose of induction hardening are the same as for flame hardening. Th

main difference is that in induction hardening the source of heat input is an induced electr

current instead of using flame.


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UNIT - II

ESSAY QUESTIONS

1 a What is meant by heat treatment? And mention it importance in manufacturing process.

b Explain the various stages of heat treatment procedure

2 a Describe the normalizing process of heat treatment.

b Differentiate between normalizing and annealing.

3 a What do you understand by hardening of steel & discuss reason why martensite is very ha

b Discuss the various characteristics of martensite transformation.

4 a Explain briefly the theory of tempering of alloy steels in the heat treatment process.

b What properties can be acquired by steel after tempering?

c Briefly explain various tempering process.

d What are the effects of tempering temperature on mechanical properties of steel?

5 a Differentiate between hardness and hardenability.

b Explain the Jominy end-quench method of determining hardenability.

c List he factors of affecting hardenability and also discuss the uses of hardenability curves.

6 a What do you understand by isothermal transformation?

b What are TTT diagrams? And how a TTT diagram has drawn?

c Draw a neat sketch of the TTT diagram for eutectoid steel and label the regions. Make the

different products formed on this diagram.

7 a What is a CCT diagram? And also write short notes on critical cooling rate?

b Describe various cooling curves on TTT diagrams. How such curves are drawn?

8 Write a short notes on the following surface heat treatment process:

(i) Carburizing (ii) Nitriding (iii) Cyaniding (iv) Carbonitriding.

9 a Explain the flame hardening process with the aid of neat sketch.

b List its advantages, disadvantages, and applications of flame hardening.

10 Compare the induction hardening and flame hardening.11 What is meant by carburizing of steels? Briefly explain the various types of carburizing?

12 Compare and contrast various surface heat treatment techniques.

13 Explain the process of Nitriding? List and discuss advantages of Nitriding over carburizin

14 Explain the process of Martempering. Compare and constrast it with Austempering proces

15 Compare and contrast the process of full annealing, process annealing, stress re

annealing, spheroidise annealing and recrystallization annealing.

16 What is Annealing? Discuss the different types of annealing & compare with normalizing

unit-2 2marks questions

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