production Engineering

2. Heat Treatment
 Heating a metal or alloy to various definite
temperatures, holding these for various time durations
and cooling at various rates.
 Combination of controlled heating and cooling
determine not only the nature and distribution of
micro-constituents (which determine the properties of
a metal or alloy), but also the grain size.
Contd...

3.  Purpose of heat treatment:
1.To remove or relieve strains or stresses induced by cold
working or non- uniform cooling (for example welding):
Annealing
2. To increase strength or hardness of the material for
improved wear resistance: Hardening
3.To improve machinability: Annealing
4.To soften the material: Annealing
5. To decrease hardness and increase ductility and toughness.
(Tempering)
Contd...

4. Main Processes Include
 Annealing
 Stress Relieving
 Quench Hardening
 Tempering
 Carburizing
 Carbon Nitriding
 Age Hardening
 Ion Nitriding
Contd...

5. 6. To improve the cutting properties of tools.
7. To change or modify the physical properties of the
material such as electrical properties, magnetic
properties, corrosion resistance and heat resistance
etc.
8. Elimination of H2 gas dissolved during pickling or
electro-plating which causes brittleness.

6. IES-1992
Which of the following generally decreases in the
steel after quench-hardening?
1. Brittleness
2. Percentage elongation
3. Impact strength
(a) 1 and 2 only (b) 2 and 3 only
(c) 1 and 3 only (d) 1, 2 and 3

7. Fig. TTT diagram for eutectoid transformation in Fe-C

8. Fig. Transformations involving austenite for Fe-C system

10.  Critical Rate of Cooling: The minimum rate of cooling at
which the austenite is transformed into martensite alone.
 Spheroidite: If pearlite is heated just below the eutectoid
temperature (say 700°C) and held at this temperature for a
day or so, the cementite lamelle in pearlite get
transformed to spherical shape. The structure is called
"spheroidite".
 This structure is less conducive to stress concentration
because of spherical grains, as compared to cementite
(lamelle structure).
 This, spheroidite is more tough but less hard as compared
to pearlite.

11. GATE-2003
During heat treatment of steel, the hardness of
various structures in increasing order is
(a) Martensite, fine pearlite, coarse pearlite,
spherodite
(b) Fine pearlite, coarse pearlite, spherodite,
martensite
(c) Martensite, coarse pearlite, fine pearlite,
spherodite
(d) Spherodite, coarse pearlite, fine pearlite,
martensite

12. GATE-1996
The iron-carbon diagram and the TTT curves are
determined under
(a) Equilibrium and non-equilibrium conditions
respectively
(b) Non-equilibrium and equilibrium conditions
respectively
(c) Equilibrium conditions for both
(d) Non-equilibrium conditions for both

13. IES-2002
TTT diagram indicates time and temperature
transformation of
(a) Cementite (b) Pearlite
(c) Ferrite (d) Austenite

14. IES-1998
Two cooling curves A and B for a eutectoid iron-
carbon alloy are superimposed on a continuous
cooling transformation diagram as shown in the
given figure. Fine pearlite microstruc-ture is
represented by the points labelled
(a) I and III
(b) II
(c) IV
(d) I

15. IAS-2002
Two plain carbon steel specimens having 0·8%
carbon content are welded. If we observe the
weldment under Metallurgical Microscope from
centre towards either side, the following
structures are observed at different zones:
1. Fine Pearlite
2. Coarse Pearlite
3. Martensite
Select the correct sequence using the codes given
below:
Codes:
(a) 1, 2, 3 (b) 1, 3, 2
(c) 2, 1, 3 (d) 3, 1, 2

16. GATE-1997
On completion of heat treatment, the resulting
structure will have retained Austenite if
(a) Rate of cooling is greater than the critical cooling
rate
(b) Rate of cooling is less than the critical cooling rate
(c) Martensite formation starting temperature is
above the room temperature
(d) Martensite formation finish temperature is below
the room temperature

17. Annealing processes
 Annealing is a heat treatment process in which the
material is taken to a high temp. kept there for some
time and then cooled in furnace.
 Cooling is done slowly to avoid the distortion.
Contd...

18.  Benefits of annealing are:
• relieve stresses
• increase softness, ductility and toughness
• produce a specific microstructure
 Depending on the specific purpose, annealing is
classified into various types: process annealing, stress
relief, full annealing and normalizing.

19. Full annealing
 Metal is heated above the upper critical temperature &
held there until the temperature of the work piece is
uniform throughout, and finally cooling the work
piece at a slowly controlled rate in furnace so that the
temperature of the surface and that of the centre of the
workpiece is approximately the same.

20. IES 2010
Consider the following statements regarding annealing
process:
1. All structural imperfections are removed
2. The hypoeutectoid steel is heated to about 50 – 70° C below
upper critical temperature.
3. Cooling can be done in heat treating furnace, by heating it,
keeping the metal in it and turning off furnace till it cools to
room temperature.
4. Uniform grain structure is resulted.
Which of these statements are correct?
(a) 1, 2 and 3 only (b) 2, 3 and 4 only
(c) 1, 3 and 4 only (d) 1, 2, 3 and 4

21. IES-1999
Heating the hypoeutectoid steels to 30oC above
the upper critical temperature line, soaking at
that temperature and then cooling slowly to room
temperature to form a pearlite and ferrite
structure, is known as
(a) Hardening (b) Normalizing
(c) Tempering (d) Annealing

22. IES-1993
Which of the following statements are true of
annealing of steels?
1. Steels are heated to 500 to 700°C.
2. Cooling is done slowly and steadily.
3. Internal stresses are relieved.
4. Ductility of steel is increased.
Select the correct answer using the codes given below:
Codes:
(a) 2, 3 and 4 (b) 1, 3 and 4
(c) 1, 2 and 4 (d) 1, 2 and 3

23. IES-1992
Temperature required for full annealing in hyper-
eutectoid steel is
(a) 50°C above upper critical temperature (AC3)
(b) 50°C below upper critical temperate (AC3)
(c) 50°C above lower critical temperature (AC1)
(d) 50°C below lower critical temperature (AC1)

24. IES – 2003
Primary object of full annealing is to
(a) Increase toughness and yield point
(b) Reduce ductility and resilience
(c) Remove foreign impurities and improve surface
finish
(d) Increase ductility and machinability

25. Process annealing
 After cold working the metal can be softened by
process annealing or "recrystallization“ to reduce the
distortions of the crystal lattice produced by cold
working.
Contd...

26. IES-2005
The complete phase recrystallization and fine
grain structure is obtained in casting, forging and
rolled parts by:
(a) Recrystallization annealing (b) Normalizing
(c) Spheroidizing (d) Austenising

27. Isothermal annealing
 Increases the machinability.
 Heat above the upper critical point and held for some
time, then rapidly cool to a temp. 600 - 700°C, and is
held at this new temperature until the austenite is
completely decomposed to form pearlite.
 Finally cooled in still air.
Contd...

28. IES 2010
Isothermal annealing is mainly used in alloy
steels to improve
(a) Machinability
(b) Toughness
(c) Ductility
(d) Weld ability

29. Stress relief annealing
 Stress relief annealing process consists of three steps.
 The first step is heating the cold worked steel to a
temperature between 5000 C and 550oC C i.e. below its
recrystallization temperature.
 The second step involves holding the steel component
at this temperature for 1-2 hours.
 The final step is to cool the steel component to room
temperature in air.
 It partly relieves the internal stress in cold worked steels
without loss of strength and hardness i.e. without change in
the microstructure. Since only low carbon steels can be cold
worked, the process is applicable to hypoeutectoid steels
containing less than 0.4% carbon.

30. GATE 2014 (PI)
For a metal alloy, which one of the following descriptions
relates to the stress-relief annealing process?
(a) Heating the workpiece material above its
recrystallization temperature, soaking and then cooling
in still air
(b) Heating the workpiece material below its
recrystallization temperature, holding for some time and
then furnace cooling
(c) Heating the workpiece material up to its
recrystallization temperature and then rapid cooling
(d) Heating the workpiece up to its recrystallization
temperature and cooling to room temperature
alternately for a few cycles

31. Normalizing
Main objective
1. Refine grain, improve machinability, tensile strength and
structure of weld.
2. Remove cold worked stess.
3. Remove dislocations due to hot working.
Process
 Heat the steel from 30°C to 50°C above its upper critical
temp, held about fifteen minutes and then allowed to cool
down in still air.
 Homogeneous structure provides a higher yield point,
ultimate tensile strength and impact strength with lower
ductility to steels.
Contd...

32. GATE-2014
The process of reheating the reduce its brittleness
without any significant loss in its hardness is
(a) normalizing (b) annealing
(c) quenching (d) tempering

33. IES 2011
Which one of the following statements is NOT
correct for normalizing?
(a) It is often applied to casting to relieve stresses
(b) It increases strength of medium carbon steel to
some extent
(c) Better surface finish can be obtained in
machining
(d) It increases grain size

34. IES-2000
Assertion (A): Normalized steel will have lower
hardness than annealed steel.
Reason (R): The pearlite of normalized steel is
finer and has lower intermolecular space.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is not the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

35. Spheroidizing
 Heat them to slightly above the critical
temperature, hold them at this temp for a period
of time, and then letting them cool in the furnace.
 Spheroidizing produces a rounded or globular form of
carbide.
 It improve abrasion resistance.

36. GATE-2006
The main purpose of spheroidising treatment is to
improve
(a) Harden ability of low carbon steel
(b) Mach inability of low carbon steels
(c) Harden ability of high carbon steels
(d) Mach inability of high carbon steels

37. IES-2003
Globular form of cementite in the structure of
steel is obtained through
(a) Normalizing
(b) Malleabilising
(c) Spheroidizing
(d) Carbonizing

38. Brine 1.20 to 1.30
Water
Water + NaOH
or KOH
1
<1
Oil 0.40 to 0.50
Forced air 0.03
Still air 0.02
Comparative cooling rates of Quench Media
 Quenching is heat treatment process where material is
cooled at a rapid rate from elevated temperature to
produce Martensite phase.
 Brine has fastest cooling rate of steel quenching and is
also used as secondary refrigerant.
Quenching

39. Hardenability
 The depth and hardness achieved by quenching is called
hardenability. Hardenability should not be confused
with hardness. Hardenability can be defined as the
depth to which a certain hardness level can be obtained
by the quenching process.
 When thick sections are involved in the hardening process,
the interiors would experience somewhat lower cooling rates
due to slower heat transfer through metal than from the
surface. As a result, the hardness of the material during
quenching gradually changes as depth from the surface
increases. The variation would be more for thick sections
than the thin sections. High hardenability steel would be
able to be thoroughly hardened without too severe a
quenching rate.

40.  In the test, the specimen (a round 100 mm long test bar)
made from the particular alloy, is first austenised in a
protective atmosphere, that is, heated to the proper
temperature to form 100% austenite. It is then quenched at
one end with a stream of water at 24°C.
 Measures of Hardenability: 50% Martensite Method:
This is the simplest method of numerically evaluating the
hardenability. It is in terms of the distance from the
quenched end (100% martensite) to the point within the
piece that is just 50% martensite. This point is the point of
steepest slope of the Jominy curve, that is, at the point of
'inflection‘.
Jominy Test
Or end quench hardenability test

41. Variation of hardness across the depth of C50 steel bar
after quenching

43. GATE-2016
The “Jominy test” is used to find
(a) Young’s modulus
(b) Hardenability
(c) Yield Strength
(d) Thermal conductivity

44.  Tempering is the process of heating martensitic steel at
a temperature below the eutectoid transformation
temperature to make it softer and more ductile.
 During the tempering process, Martensite transforms to
a structure containing iron carbide particles in a matrix
of ferrite.
Tempering

45. IES 2010
Match List I with List II and select the correct
answer using the code given below the lists:
List I List II
(Quenching media) (Structure produced)
A. Water 1. Coarse pearlite
B. Oil 2. Martensite
C. Air 3. Very fine pearlite
D. Furnace cools 4. Fine pearlite
A B C D A B C D
(a) 1 3 4 2 (b) 2 3 4 1
(c) 1 4 3 2 (d) 2 4 3 1

46. IES-2001
Consider the following quenching media:
1. Oil 2.Water
3. Water + NaOH 4. Brine
The correct sequence of these media in order of
increasing hardness of steel undergoing heat
treatment is
(a) 1, 3, 2, 4 (b) 2, 1, 3, 4
(c) 1, 2, 3, 4 (d) 4, 3, 2, 1

47. IES-2009
Which one of the following mediums is used for
the fastest cooling rate of steel quenching?
(a) Air (b) Oil
(c) Water (d) Brine

48. IES-2006
Match List-I (Effect of Cooling) with List-II (Cooling
Medium) and select the correct answer using the code
given below:
List -I List - II
A. Martensite 1. Water quenched
B. Very fine pearlite 2. Air cooled
C. Fine pearlite 3. Furnace cooled
D. Coarse pearlite 4. Oil quenched
A B C D A B C D
(a) 1 4 2 3 (b) 2 3 1 4
(c) 2 3 4 1 (d) 1 2 3 4

49. Martempering
 Quench steel from the austenizing temperature to a
bath just above Ms.
 Since, austenite transforms to martensite
simultaneously throughout the steel, the distortion in
quenching is minimized.
 This induces greater toughness in the steel.

51. Austempering
 This hardening process is basically the same as the
martempering, but has a longer holding time above
the martensitic transformation temperature.

53. GATE-2004
From the lists given below, choose the most appropriate set of
heat treatment process and the corresponding process
characteristics
Process Characteristics
P. Tempering 1. Austenite is converted into
bainite
Q. Austempering 2. Austenite is converted into
martensite
R. Martempering 3. Cementite is converted into
globular structure
4. Both hardness and brittleness are
reduced
5. Carbon is absorbed into the metal
(a) P-3 Q-1 R-5 (b) P-4 Q-3 R-2
(c) P-4 Q-1 R-2 (d) P-1 Q-5 R-4

54. IES-1994
Consider the following treatments:
1. Normalizing 2. Hardening
3. Martempering 4. Cold working
Hardness and tensile strength in austenitic stainless
steel can be increased by
(a) 1, 2 and 3 (b) 1 and 3
(c) 2 and 4 (d) 4 alone

55. IES-2006
Tempering is a process of annealing
(a) Martensite at low temperatures
(b) Martensite at higher temperatures
(c) Bainite at low temperatures
(d) Bainite at higher temperatures

56. IES-2005
Austempering is employed to obtain:
(a) 100% martensitic structure
(b) 100% bainitic structure
(c) 50% martensitic and 50% bainitic structure
(d) 100% pearlitic structure

57. IES-2004
Consider the following pairs:
Heat treatment Effect on medium carbon steel
1. Normalizing : Grain refinement
2. Full annealing : Uniform grain structure
3. Martempering : Decreased ductility
4. Spheroidizing : Maximum softness
Which of the pairs given above are correctly matched?
(a) 1 and 2 (b) 2 and 3
(c) 3 and 4 (d) 1, 2, 3 and 4

58. IES-2001
'Tempering' of quenched martensitic steel is
necessary to improve the
(a) Hardness of the metal
(b) Surface texture or the metal
(c) Corrosion resistance of the metal
(d) Ductility or the metal

59. IES-2006
The pattern known as Widmanstatten structure is
encountered in:
(a) Tempering (b) Normalizing
(c) Spheroidizing (d) Annealing

60. GATE-2014Match the heat treatment processes (Group A) and their
associated effects on properties (Group B) of medium
carbon steel
P Q R S P Q R S
(a) III IV II I (b) II III IV I
(c) III II IV I (d) II III I IV
Group A Group B
P: Tempering I. Strengthening and grain refinement
Q: Quenching II. Inducing toughness
R: Annealing III. Hardening
S: Normalizing IV. Softening

61. Solutionizing
 Solutionizing (solution heat treatment), where the
alloy is heated to a temperature between solvus and
solidus temperatures and kept there till a uniform
solid-solution structure is produced.

62. GATE-2016
In the phase diagram shown in the figure, four
samples of the same composition are heated to
temperatures marked by a, b, c and d.
At which temperature
will a sample get
solutionized the
fastest?
(a)a (b) b
(c) C (d) d

63. Aging
 Aging finely dispersed precipitate particle will form.
Aging the alloy at room temperature is called natural
aging, whereas at elevated temperatures is called
artificial aging. Most alloys require artificial aging, and
aging temperature is usually between 15-25% of
temperature difference between room temperature and
solution heat treatment temperature.

64. Case Hardening
 In case hardening, the surface of the steel is made
hard and wear resistant, but the core remains soft
and tough.

65. Induction hardening
 Alternating current of high frequency passes for few
second through an induction coil enclosing the steel
part to be heat treated.
 Immediately after heating, water jets are activated to
quench the surface.
 Martensite is produced at the surface, making it
hard and wear resistant.

66. GATE-2000
Cast steel crankshaft surface is hardened by
(a) Nitriding (b) Normalising
(c) Carburising (d) Induction heating

67. IES-1992
Induction hardening is basically a
(a) Carburising process
(b) Surface hardening process
(c) Core-hardening process
(d) None of the above

68. Flame hardening
 For large work pieces flame hardening is done by
means of an oxyacetylene torch.
 Heating should be done rapidly by the torch and the
surface quenched.

69. IES-1996; 1997
Guideways of lathe beds are hardened by
(a) Carburising
(b) Cyaniding
(c) Nitriding
(d) Flame hardening

70. Laser hardening
 Laser beams are of high intensity, a lens is used to
reduce the intensity by producing a defocused spot of
size ranging from 0.5 to 25 mm.

71. Carburizing
 Carburizing is the most widely used method of surface
hardening.
 Here, the surface layers of low carbon steel are
enriched with carbon up to 0.8-1.0%. The source of
carbon may be a solid medium, a liquid or a gas.
 In all cases, the carbon enters the steel at the surface
and diffuses into the steel as a function of time at an
elevated temperature.
 Carburizing is done at 920-950oC.
Contd...

72.  There is fully austenitic state is essential. If carburizing
is done in the ferritic region, the carbon, with very
limited solubility in ferrite, tends to form massive
cementite particles near the surface, making the
subsequent heat treatment difficult.
 For this reason, carburizing is always done in the
austenitic state, even though longer times are required
due to the diffusion rate of carbon in austenite being
less that in ferrite at such temperatures.

73. IES 2011
Assertion (A): Carburizing is used for machine
elements which have to have a wear resistant
working surface.
Reason (R) : The composition of surface layers
are changed in carburizing.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is NOT
the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

74. GATE-1992
Carburized machine components have high
endurance limit because carburization
(a) Raises the yield point of the material
(b) Produces a better surface finish
(c) Introduces a compressive layer on the surface
(d) Suppresses any stress’s, concentration produced in
the component.

75. IES-1992
In case carburising Carbon is introduced to form a
high carbon layer at the surface. The carbon is
introduce in the form of
(a) Graphite flakes (b) Pearlite
(c) Cementite (d) Free carbon

76. IES-2005
If the surface of a component is heavily stressed
while the stresses in the core are of comparative
small magnitude, which one of the following heat
treatment methods is employed?
(a) Annealing (b) Tempering
(c) Quenching (d) Case hardening

77. Cyaniding
 Cyaniding is done in a liquid bath of NaCN, with the
concentration varying between 30 and 97%.
 The temperature used for cyaniding is lower than that
for carburizing and is in the range of 800-870oC.
 The time of cyaniding is 1-3 hr to produce a case depth
of 0.25 mm or less.

78. GATE-2003
Hardness of steel greatly improves with
(a) Annealing (b) Cyaniding
(c) Normalising (d) Tempering

79. Nitriding
 During nitriding, pure ammonia decomposes to yield
nitrogen which enters the steel.
 The temperature of nitriding is 500-590oC. The time
for a case depth of 0.02 mm is about 2 hr.
 Most of the nitrogen, that enters the steel, forms hard
nitrides (e.g., Fe3N).
 No phase change occurs after nitriding.

80. IES-1992
Quenching in not necessary when hardening is
done by
(a) Case carburizing
(b) Flame hardening
(c) Nitriding
(d) Any of the above processes

81. IES-1995
Match List I with List II and select the correct answer
using the codes given below the lists:
List I (Heat treatment) List II (Effect on the
properties)
A. Annealing 1. Refined grain structure
B. Nitriding 2. Improves the hardness of
the whole mass
C. Martempering 3. Increases surface hardness
D. Normalising 4. Improves ductility
Codes:A B C D A B C D
(a) 4 3 2 1 (b) 1 3 4 2
c) 4 2 1 3 (d) 2 1 3 4

82. IES-2004
Match List I (Name of treatment) with List II (Media
used) and select the correct answer using the codes
given below the Lists
List I List II
A. Pack carburizing 1. Ammonia gas
B. Gas carburizing 2. Sodium cyanide
C. Cyaniding 3. Carburizing
compound
D. Nitriding 4. Ethane
Codes:A B C D A B C D
(a) 3 4 2 1 (b) 2 1 3 4
(c) 3 1 2 4 (d) 2 4 3 1

83. Precipitation & Dispersion hardening
 Foreign particles can also obstructs movement of
dislocations i.e. increases the strength of the material.
 Foreign particles can be introduced in two ways –
precipitation and mixing-and-consolidation technique.
 Precipitation hardening is also called age hardening
because strength increases with time.
 Requisite for precipitation hardening is that second phase
must be soluble at an elevated temperature but precipitates
upon quenching and aging at a lower temperature.
 E.g.: Al-alloys, Cu-Be alloys, Mg-Al alloys, Cu-Sn alloys
 If aging occurs at room temperature – Natural aging
 If material need to be heated during aging – Artificial
aging.
Contd...

84.  In dispersion hardening, fine second particles are
mixed with matrix powder, consolidated, and pressed
in powder metallurgy techniques.
 For dispersion hardening, second phase need to have
very low solubility at all temperatures.
 E.g.: oxides, carbides, nitrides, borides, etc.
 Dislocation moving through matrix embedded with
foreign particles can either cut through the particles or
bend around and bypass them.
 Cutting of particles is easier for small particles which
can be considered as segregated solute atoms. Effective
strengthening is achieved in the bending process,
when the particles are submicroscopic in size.
Contd...

85.  Optimum strengthening occurs during aging once the right
interspacing of particles is achieved.
 Smaller the particles, dislocations can cut through them at
 lower stresses
 larger the particles they will be distributed at wider
distances.

86. IES-2009
Which one of the following materials can be
subjected to an age hardening process?
(a) HSS
(b) Aluminium
(c) Pure iron
(d) Stellite

87. IES-1994; 2005
Assertion (A): Carburizing is done on non-ferrous
alloys to increase the surface hardness.
Reason (R): Precipitation hardening of non-
ferrous alloys involves solution heat treatment
followed by precipitation heat treatment.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is not the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

88. IES 2007
Which one among the following is the most
effective strengthening mechanism of non-
ferrous metal?
(a) Solid solution hardening
(b) Strain hardening
(c) Grain size refinement
(d) Precipitation hardening

89. IES-2001
Which one of the following pairs is correctly
matched?
(a) Solid solution strengthening… Increasing density
of dislocations
(b) Dispersion hardening ………..Creating strained
region in the crystal
(c) Strain-hardening …………....Creating particles to
resist the movement
of dislocations
(d) Precipitation-hardening….. Creating particles by
decreasing solubility of one
phase in another

90. Grain growth
 Grain growth follows complete crystallization if the
material is left at elevated temperatures.
 Grain growth does not need to be preceded by recovery
and recrystallization; it may occur in all polycrystalline
materials.
 In contrary to recovery and recrystallization, driving force
for this process is reduction in grain boundary energy.
 Tendency for larger grains to grow at the expense of smaller
grains is based on physics.
 In practical applications, grain growth is not desirable.
 Incorporation of impurity atoms and insoluble second
phase particles are effective in retarding grain growth.
 Grain growth is very strongly dependent on temperature.

91. Season cracking or stress-corrosion
cracking.
 Brasses with more than 15% zinc often experience
season cracking or stress-corrosion cracking.
 Both stress and exposure to corrosive media are
required for this failure to occur (but residual stresses
and atmospheric moisture may be sufficient!).
 As a result, cold-worked brass is usually stress relieved
(to remove the residual stresses) before being placed in
service.

92. IES 2007
Which one of the following elements/ alloy
exhibits season cracking?
(a) Iron (b) Brass
(c) Aluminium (d) Steel

93. IAS 1994
Major operations in the manufacture of steel balls
used for Ball bearings are given below
1. Oil lapping 2. Cold heading
3. Annealing 4. Hardening
5. Rough grinding
The correct sequence of these operations is
(a) 3,2,4,1,5 (b) 3,2,1,4,5
(c) 2,3,4,5,1 (d) 2,3,5,4,1

94. IES 2011
Assertion (A) : The steel when heated above a
certain temperature and cooled to room
temperature, structure adjustment stabilizes.
Reason (R) : The modification is mainly based
on cooling rate.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is NOT
the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

95. Strengthening mechanisms in
Metals
 Ability of a metal to deform plastically depends on ease of
dislocation motion under applied external stresses.
 As strengthening of a metal consist hindering dislocation
motion. Dislocation motion can be hindered in many
ways, thus are strengthening mechanisms in metals.
 Strengthening by methods of grain-size reduction, solid-
solution alloying and strain hardening applies for single-
phase metals.
 Precipitation hardening, dispersion hardening, fiber
strengthening and Martensite strengthening are applicable
to multi-phase metallic materials.

96. Strengthening by Grain Size
Reduction
 This strengthening mechanism is based on the fact
that crystallographic orientation changes abruptly in
passing from one grain to the next across the grain
boundary.
 Thus it is difficult for a dislocation moving on a
common slip plane in one crystal to pass over to a
similar slip plane in another grain, especially if the
orientation is very misaligned.
 In addition, the crystals are separated by a thin non-
crystalline region, which is the characteristic structure
of a large angle grain boundary.
Contd…

97.  With decrease in grain size, the mean distance of a
dislocation can travel decreases, and soon starts pile
up of dislocations at grain boundaries. This leads to
increase in yield strength of the material.
 Grain size reduction improves not only strength, but
also the toughness of many alloys.
 Grain size can be controlled by rate of cooling, and also
by plastic deformation followed by appropriate heat
treatment.

98. IES-1998
Assertion (A): Refining the grain size of a
polycrystalline material renders it harder and
stronger.
Reason (R): Grain boundaries provide easy paths to
dislocation motion.
(a) Both A and R are individually true and R is the correct
explanation of A
(b) Both A and R are individually true but R is not the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

99. GATE-1998
Decreasing grain size in a polycrystalline material
(a) Increases yield strength and corrosion resistance.
(b) Decreases yield strength and corrosion resistance
(c) Decreases yield strength but increases corrosion
resistance
(d) Increases yield strength but decreases corrosion
resistance.

100. IES 2010
Assertion (A): Polycrystalline material is stronger
than ordinary one.
Reason (R): Crystals in polycrystalline material
have different orientations with respect to each
other.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is NOT the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

101. Solid Solution
 A solid solution is formed when two metals are
completely soluble in liquid state and also completely
soluble in solid state. In other words, when
homogeneous mixtures of two or more kinds of atoms
(of metals) occur in the solid state, they are known as
solid solutions.
 The more abundant atomic form is referred as solvent
and the less abundant atomic form is referred as
solute.
 Example is brass. Brass is a solid solution of copper (64
percent) and zinc (36 percent). In this case copper
atoms are solvent atoms whereas zinc atoms are solute
atoms.

102. TYPES OF SOLID SOLUTIONS
 Solid solutions are of two types.
 They are:
(a) Substitutional solid solutions.
(b) Interstitial solid solutions.

103. 1. Substitutional Solid Solutions
 If the atoms of the solvent or parent metal are replaced
in the crystal lattice by atoms of the solute metal then
the solid solution is known as substitutional solid
solution.
 For example, copper atoms may substitute for nickel
atoms without disturbing the F.C.C. structure of
nickel.
 In the substitutional solid solutions, the substitution
can be either disordered or ordered.
 Hume Rothery formulated certain rules which govern
the formation of substitutional solid solutions.

104. Solid solubility
 Extent of solid solubility in a two element system can be
predicted based on Hume-Ruthery conditions.
 If the system obeys these conditions, then complete solid
solubility can be expected.
Hume-Ruthery conditions:
 Crystal structure of each element of solid solution must be
the same.
 Size of atoms of each two elements must not differ by more
than 15%.
 Elements should not form compounds with each other i.e.
there should be no appreciable difference in the electro
negativities of the two elements.
 Elements should have the same valence.

105. 2. Interstitial Solid Solutions
 In interstitial solid solutions, the solute atom does not
displace a solvent atom, but rather it enters one of the
holes or interstices between the solvent atoms.
 An excellent example is iron-carbon system which is
shown in Fig.
Contd…

106.  In this system the carbon (solute atom) atom occupies
an interstitial position between iron (solvent atom)
atoms.
 Normally, atoms which have atomic radii less than one
angstrom are likely to form interstitial solid solutions.
 Examples are atoms of carbon (0.77 A°), nitrogen (0.71
A°), hydrogen (0.46 A°), Oxygen (0.60 A°) etc.

107. IES 2011
Assertion (A) : Solid solutions of metal are
crystal whose properties are close to those of
the solvent.
Reason (R) : They retain the same crystal lattice
and type of bond.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is NOT
the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

108. INTERMETALLIC COMPOUNDS
 Intermetallic compounds are generally formed when
one metal (for example magnesium) has chemical
properties which are strongly metallic and the other
metal (for example antimony, tin or bismuth) has
chemical properties which are only weakly metallic.
 Examples of intermetallic compounds are Mg2Sn,
Mg2Pb, Mg3Sb2 and Mg3 Bi2.
 These intermetallic compounds have higher melting
point than either of the parent metal.
 This higher melting point indicates the high strength
of the chemical bond in intermetallic compounds.

109. IES-2001
Which of the following factors govern solubility of
two non-ferrous metals both in liquid state, as
well as in solid state?
1.Crystal structure 2.Relative size factor
3.Chemical-affinity factor 4.Relative valence
factor
Select the correct answer using the codes given below:
Codes:
(a) 1, 2 and 3 (b) 2, 3 and 4
(c) 1 and 4 (d) 1, 2, 3 and 4

110. IES 2010
Consider the following:
1. Crystal structure 2. Relative size
3. Chemical affinity 4. Valency
Which of these factors govern relative
solubility of two metals in each other in the
solid state?
(a) 1, 2 and 3 only
(b) 2, 3 and 4 only
(c) 1, 2 and 4 only
(d) 1, 2, 3 and 4

111. IES-2006
Which one of the following factors is more
relevant to represent complete solubility of two
metals in each other?
(a) Chemical affinity (b) Valency factor
(c) Crystal structure factor (d) Relative size factor

112. Allotropic transformation
 When metals solidify, they assume a crystalline structure; that
is, the atoms arrange themselves in a geometric lattice.
 Many metals exist in only one lattice form. Some, however, can
exist in the solid state in two or more lattice forms, the particular
form depending on the conditions of temperature and pressure.
Such metals are said to be allotropic or polymorphic, and the
change from one lattice form to another is called an allotropic
transformation.
 The most notable example of such a metal is iron, where the
allotropic change makes it possible for heat-treating procedures
to produce a wide range of final properties.
 It is largely because of its allotropy that iron has become the
basis of our most important alloys.

113. IES 2010
An allotropic material has
(a) Fixed structure at all temperatures
(b) Atoms distributed in random pattern
(c)Different crystal structures at different
temperatures
(d) Fixed structure but random atom distribution

114. The End

115. The End