Laboratory Manual of
MATERIAL SCIENCE AND METALLURGY
(3131904)
III Semester
“BACHELOR OF ENGINEERING”
IN MECHANICAL ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
GOVERNMENT ENGINEERING COLLEGE-PATAN
AT. KATPUR (PATAN) – 384265

GOVERNMENT ENGINEERING COLLEGE-PATAN
AT. KATPUR (PATAN) - 384265
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MATERIAL SCIENCE AND METALLURGY (3131904) and recorded in the
journal/manual is bonafide work of
Mr./Ms._____________________________________ Enrollment
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_____/________ in the branch of Mechanical Engineering. This has been
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MATERIAL SCIENCE AND METALLURGY
(3131904)
INDEX
SR
NO
DATE TITLE OF EXPERIMENT PAGE GRADE SIGN
1
To get acquainted with the operation, construction,
use and capabilities of a metallographic
microscope.
2
To study procedure of specimen preparation for
microscopic examination and to carry out a
specimen preparation.
3
To understand what is micro examination,
importance of micro examination and to study
various ferrous, non-ferrous microstructures.
4
To identify the different types of material available
for design, manufacturing and processing of
various components based on structure-property-
performance-processing relationships.
5
To show the effect of different quenching media
(Oil, Water and Brine) on the hardness of medium
carbon steel.
6
To understand the concept of hardenability and its
relevance to heat treatment procedure to be
adopted in practice.
7
To find out the effect of varying section size on
hardenability of steel and obtain hardness
distribution curves of hardened steel cross-section.
8
Study of different heat treatment processes-
annealing, normalizing, hardening and tempering,
surface and casehardening to improve properties
of steel during processes and applications.
9
To understand the procedure of testing, nature of
indication, the capability and sensitivity of the
liquid penetrant test and the magnetic particle test.
10
To understand the procedure of testing, nature
of indication, the capability and sensitivity of
the Eddy current test and the Ultrasound test.

1
Experiment No.-1
Aim: To get acquainted with the operation, construction, use and capabilities
of a metallographic microscope.
Learning Outcomes:
 Principle on Metallurgical microscope work
 How to examine specimens using microscope.
Introduction:
The metallurgical microscope is the most important tool of the metallurgist. It consist an
objective and an eye-piece. Its primary function is to reveal the details of the object. The clarity
and the extent to which the details are revealed depend on the degree to which these optical
systems are created.
Fig. Metallurgical microscope
Metallography is the general study of metals and their behaviour, with particular reference to
their microstructure and macro-Structure.

2
Principle:
Bright-field illumination:
Metallurgical microscopes differ from biological microscopes primarily in the manner by which the
specimen is illuminated. Unlike biological microscopes, metallurgical microscopes must use reflected
light. Figure 1 presents a simplified ray diagram of the illuminating and imaging system of a
metallurgical microscope.
Fig. Image formation in a metallurgical microscope employing bright-field illumination
The conventional form of illumination by which metallographic specimens are illuminated for
microscopic examination is known as bright-field illumination --a condition of lighting that
renders a dark image on a bright, well-lit background field. Bright-field illumination is obtained
by means of a vertical illuminator which is mounted in back of the microscope objective. Light
from the light source is directed into the vertical illuminator. Deviation of the incident light beam
from the vertical illuminator into the objective is most commonly achieved by a plane-glass
reflector or a half-silvered mirror inclined at a 45o
angle to the axis of the incoming light from the
source. The incident light hits the glass plate and is specularly reflected down along the optical
axis of the microscope into the objective.
The prepared specimen (polished or etched) is placed on the microscope stage, its surface
perpendicular to the optical axis of the microscope. It is illuminated by the light which emerges
from the objective lens and which has been focused so that the beam is approximately parallel to
the optical axis of the microscope. Thus the light incident upon the specimen is virtually normal
to the surface plane of the specimen. This form of illumination is called "vertical illumination";
the specimen and the light incident upon it are at right angles to one another.

3
Light incident upon the specimen is reflected back from the specimen surface. Any light that
reflects back from specimen features which are approximately normal to the optical axis (i.e.
features that are perpendicular to the incident light beam) will enter the objective, pass through
the plane glass reflector, travel on to the eyepiece, and will form the bright portion of the image
one sees. Any light that is reflected back from features inclined to the optical axis (i.e. features
that are not perpendicular to the incident light beam) will be scattered and will not enter the
objective. Such features will thereby appear dark in the image one sees. The final image of the
specimen, formed by the eyepiece(s) of the microscope, is thus bright for all features normal to
the optical axis and dark for inclined features. In this way, the various micro structural features of
a metallographic specimen --such as grain boundaries that have been etched to produce grooves
with inclined edges, precipitate particles, and non-metallic inclusions --are all revealed in the
image of the specimen. Figure presents a schematic diagram showing bright and dark image
areas corresponding to reflection from normal or inclined features on the specimen surface.
Fig. Specimen image under bright-field illumination.
Microscope Basic Functions:
An optical microscope consists of the following two major basic functions.
1. Creating a Magnified Image of a Specimen
2. Illuminating a Specimen

4
Microscope Parts and Functions:
1. Eyepiece: The eyepiece (sometimes called the 'ocular') is the lens of the microscope closest to
the eye that you look through. It is half of the magnification equation (eyepiece power multiplied
by objective power equals magnification), and magnifies the image made by the objective lens.
sometimes called the virtual image. Eyepieces come in many different powers. One can identify
which power any given eyepiece is by the inscription on the eyecup of the lens, such as "5x",
"10x", or "15X". Oculars are also designed with different angles of view; the most common is the
wide field (W.F.).
2. Eyepiece Holder: This simply connects the eyepiece to the microscope body, usually with a
setscrew to allow the user to easily change the eyepiece to vary magnifying power.
3. Body: The main structural support of the microscope which connects the lens apparatus to the
base.
4. Nose Piece: This connects the objective lens to the microscope body. With a turret, or rotating
nose piece as many as five objectives can be attached to create different powers of magnification
when rotated into position and used with the existing eyepiece.
5. Objective: The lens closest to the object being viewed which creates a magnified image in an
area called the "primary image plane". This is the other half of the microscope magnification
equation (eyepiece power times objective power equals magnification). Objective lenses have
many designs and qualities which differ with each manufacturer. Usually inscribed on the barrel
of the objective lens is the magnification power and the numerical aperture (a measure of the
limit of resolution of the lens).
6. Focusing Mechanism: Adjustment knobs to allow coarse or fine (hundredths of a millimeter)
variations in the focusing of the stage or objective lens of the microscope.

5
7. Stage: The platform on which the prepared slide or object to be viewed is placed. A slide is
usually held in place by spring-loaded metal stage clips. More sophisticated high-powered
microscopes have mechanical stages which allow the viewer to smoothly move the stage along
the X (horizontal path) and Y (vertical path) axis. A mechanical stage is a must for high-power
observing.
8. Illumination Source: The means employed to light the object to be viewed. The simplest is
the illuminating mirror which reflects an ambient light source to light the object. Many
microscopes have an electrical light source for easier and more consistent lighting. Generally
electrical light sources are either tungsten or fluorescent, the fluorescent being preferred because
it operates at a cooler temperature. Most microscopes illuminate from underneath, through the
object, to the objective lens. On the other hand, stereo microscopes use both top and bottom
illumination.
9. Base: The bottom or stand upon which the entire microscope rests or is connected.
10. Photography unit with CMOS or CCD sensor able to make pictures via microscope.
The total magnification of the microscope may be calculated by the formula:
M = L x E / F
Where, L- The distance from back of objective to eyepiece;
F – The focal length of the objective;
E- The magnifying power of the eyepiece.
The common magnification of metallurgical microscope is in the range x50 – x1000.
The maximum magnification obtained with the optical microscope is about 2OOOx.
.

6
Exercise No.-1
Q.-1 Explain working principle of the metallurgical microscope with neat sketch?

7
Q.-2 List different parts of microscope stating their functions.

8
Q.-3 Compare dark-field and bright field illuminations.

9
Q.-4 State major difference between metallurgical and biological microscope.
.

10
Experiment No.-2
Aim: To study procedure of specimen preparation for microscopic
examination and to carry out a specimen preparation.
Introduction:
Specimen preparation or polishing is necessary to study its micro-structure, because the
metallurgical microscope discussed earlier makes use of the principle of reflection of light (from
the specimen) to obtain the metal structure. Satisfactory metallographic results can be obtained
only, when the specimen has been carefully prepared. Even the most costly microscope will not
reveal the metal structure if the specimen has been poorly prepared. A properly prepared metal
specimen is flat, does not contain scratches, its nicely polished, and suitably etched.
Metallographic or microscopy consists of the microscopic study of the Structural characteristics
of material or an alloy. The microscope is thus the most important tool of a metallurgist from
both, scientific & technical study point view. It is possible to determine grain size & the size,
shape & distribution of various phases & inclusions which have a great effect on the mechanical
properties of metal. The microstructure will reveal the mechanical & thermal treatment of the
metal & it may be possible to predict its behavior under a given set of conditions.
Experience had indicated the success in microscopic study depends upon the case taken in the
preparation of specimen. The most expensive microscope will not reveal the structure of a
specimen that has been poorly revealed .The procedure to be followed in the preparation of a
specimen is comparatively similar and simple & involves a technique which is developed only
after constant practice. The ultimate objective is to produce a flat, scratch free, mirror like
surface. The steps involved or required to prepare a metallographic specimen properly are
covered in the coming section explained below.
Procedure
The procedure for preparing the specimen for both macro and micro-examination is the
same, except that in the later case the final surface finish is more important than in the
former.
1. Selection of specimen
When investigating the properties of a metal or alloy, it is essential that the, specimen should
be selected from that area (of the alloy plate or casting) which can be taken as representative
of the whole mass.
2. Cutting of the specimen
After selecting a particular area in the whole mass, the specimen may be removed with the
help of a saw, a trepanning tool, an abrasive wheel, etc.
3. Mounting the specimen
If the specimen is too small to be held in hand for further processing, it should be mounted
machine in the thermoplastic resin or some other low melting point alloy.

11
Mounted specimens
4. Obtaining Flat Specimen Surface
It is first necessary to obtain a reasonably flat surface on the specimen on the specimen. This
is achieved by using a fairly coarse file or machining or grinding, by using a motor driven
emery belt.
5. Intermediate and Fine Grinding
Intermediate and fine grinding is carried out using emery papers of progressively finer grade.
The emery papers should be of very good quality in respect of uniformity of particle size
Four grades of abrasives used are: 220 grit, 320 grit, 400 grit, and 600 grit (from coarse to
fine); the 320 grit has particle sizes (of the silicon carbide) as about 33 microns and 600 grit
that of 17 microns ( 1 micron =1/1000 mm).The specimen is first ground on 220 grit paper,
so that scratches are produced roughly at right angle to those initially existing on the
specimen and produced through preliminary grinding or coarse filing operation.
Having removed the primary grinding marks, the specimen is washed free of No. 220 grit.
Grinding is then continued on the No. 320 paper, again turning the specimen through 90°
and polishing until the previous scratch marks are removed. The process is repeated with the
No. 400 and No. 600 papers. Grinding with the No.200, No.320, etc., papers could be done
in the following ways:
The specimen may be hand-rubbed against the abrasive paper, which is laid over a flat
surface such as a piece of glass plate. The abrasive paper may be mounted on the surface of a
flat, horizontally rotating wheel and the specimen held, in the hand, against it. In either case,
the surface of the abrasive paper (with water proof bases) shall be lubricated with water so as
to provide a flushing action to carry away the particles cut from the surface.
Fine grinding Emery paper for grinding

12
Belt grinder Emery paper for belt grinder
6. Rough Polishing
A very small quantity of diamond powder (particle size about 6 microns) carried in a paste
that is oil-soluble is placed on the nylon cloth-covered surface of a rotating Polishing wheel.
The lubricant used during the polishing operation is specially prepared oil. The specimen is
pressed against the cloth of the rotating wheel with considerable pressure and is moved
around the wheel in the direction opposite to rotation of the wheel to ensure a more uniform
polishing action.
Double Disc polishing machine Single Disc polishing machine
7. Fine Polishing
The polishing compound used is alumina (Al2O3) power (with a particle size of 0.05
microns) placed on a cloth covered rotating wheel. Distilled water is used as a lubricant.
Fine polishing removes fine scratches and very layer remaining from the rough polishing
stage.
8. Etching
Even after fine polishing, the granular structure in a specimen usually cannot be seen under
the microscope; because grain boundaries in a metal have a thickness of the order of a few
atom diameters at best, and the resolving power of a microscope is much too low to reveal.

13
In order to make the grain boundaries visible, after fine polishing the metal specimen are
usually etched. Etching imparts unlike appearances to the metal constituents and thus makes
metal structure apparent under the microscope.
Sr.
No.
Type of
Etchant Composition Uses
1. Nital (i)Cone, Nitric acid
(ii) Absolute methyl
alcohol
2CC
98CC
For etching steels, grey cast
iron
& black head malleable.
2. Acid ammonium
persulphate
(i)Hydrochloric acid
(ii) Ammonium per-
sulphate
(iii) Water
10CC
10gms
80CC
For etching stainless steels.
3. Ammonia hydrogen
peroxide
(i)Ammonium
hydroxide (0.880)
(ii) Hydrogen peroxide
(3%solution)
(iii) Water
50CC
20-
50CC
50 CC
The best general Etchant
for copper, brasses and
bronze
4. Dilute hydrofluoric
acid
(i) Hydrofluoric acid
(ii) Water
0.5 CC
99.5
CC
A good general Etchant for
Al and its alloys (apply by
swabbing)
5. Keller’s Reagent (i)Hydrochloric acid
(ii) Hcl
(iii) HNO3
(iv) Water
1 CC
1.5 CC
2.5 CC
95 CC
For (immersion) etching of
Duralumin type alloys
6. Mixed nitric and
acetic acids
(i) Nitric acid
(ii) Glacial acetic acid
50 CC
50 CC
For etching Nickel and
Monel metal
Table. 1 Etching regents for Microscopic Examination
Method:
Before Etching, the polished specimen is thoroughly washed in running water.
Then, the etching is done either by
1. Immersing the polished surface (of the specimen) in the etching reagent or by
2. Rubbing the polished surface gently with a cotton swab wetted with the etching Reagent.
After etching, the specimen is again washed thoroughly and dried. Now, the specimen can be
studied under the microscope. Etching reagents for microscopic examination.

14
Exercise No.-2
Q.-1 What is the significance of preparation of specimen for the micro-examination.

15
Q.-2 List down various steps required for the preparation of specimen.

16
Q.-3 List at least 5 names of clothes used in wet polishing process.
Q.-4 Explain about etchant? List at least 7 names of etchant used for different materisls.

17
Experiment No.-3
Aim: To understand what is micro examination, importance of micro
examination and to study various ferrous, non-ferrous microstructures.
Introduction:
The method adopted for metallography examination can be divided in to two groups:
– Macro examination- either with the naked eye or under a very low magnification (x5-10)
– Micro examination- at high magnification (x20- 2000).
The branch of materials science dealing with microscopic examination of polished metals and
alloys specimen is called Micrography.
Study of metallic microstructures is done by using metallurgical microscope
• Can be used to determine
– Heat treatment
– mechanical processing
– material properties and
– phases present
– Case Depth
– Surface decarburization
– Coating / Plating
– Presence of weld defects, if any
Macro Examination:
Macro-Examinations are also performed on a polished and etched cross-section of a welded
material. During the examination, a number of features can be determined including weld run
sequence, important for weld procedure qualifications tests. As well as this, any defects on the
sample will be assessed for compliance with relevant specifications. Slag, porosity, lack of weld
penetration, lack of sidewall fusion and poor weld profile are among the features observed in
such examinations. It is normal to look for such defects either by standard visual examination or
at magnifications of up to 50X. It is also routine to photograph the section to provide a
permanent record. This is known as a photomacrograph.
Micro Examination
This is performed on samples either cut to size or mounted in a resin mold. The samples are
polished to a fine finish, normally one micron diamond paste, and usually etched in an
appropriate chemical solution prior to examination on a metallurgical microscope. Micro
examination is performed for a number of purposes, the most obvious of which is to assess the
structure of the material. It is also common to examine for metallurgical anomalies such as third
phase precipitates, excessive grain growth, etc. Many routine tests such as phase counting or
grain size determinations are performed in conjunction with micro-examinations.
Study of Microstructures
Study of microstructure of the specimen is required to determine the metallurgical effects of
heat-treatment manufacturing processes (such as welding) etc. Trained metallographers are able
to evaluate the microscopical appearance of metals and to indicate the past history of the metals
so that the advisability of particular metallurgical method can be predicted. Many
photomicrographs and sketches of metallic structure included in the book, because all

18
metallurgical process have definite effects on the structure of the metals used and the
metallurgical nature of processes can be studied in terms of these metallographic effects.
Microstructures of Ferrous Metal
GREY CAST IRON S.G. IRON
WHITE CAST IRON MELLEABLE CAST IRON
Microstructures of Non Ferrous Metal
BRASS ALUMINUM

19
BRONZE GUN-METAL
Difference between Micro and Macro Examination:
Micro-examination Macro-examination
1. Micro-examination or micrograph involves
the study of the structures of
metals and their alloys under a
micro-scope at magnifications form
X20 to X2000. The observed structure is
called the microstructure.
1. Macro-examination involves the
study of the structure of metals and their
alloys by the naked eye or by low
power magnification up to X15. The
observed structure is called the
macrostructure
2. Micro-examination involves much
smaller areas and brings out
information which can never be
revealed by low magnification.
2. Macro-examination gives a broad picture
of the interior of a metal by studying
relatively large sectioned areas.
3. The aim of micro-examination is
To determine the size and shape of the
crystallites which constitute an alloy.
To reveal structures characteristic of certain
types of mechanical working operations.
To discover micro defects
To determine the chemical content of alloys
To indicate quality of heat treatment,
mechanical properties.
3. The aim of macro-examination is
To reveal the size, form and
arrangement of crystallites.
To reveal fibers in deformed metals.
To reveal shrinkage porosity and gas cavities
To reveal cracks appearing during certain
fabrication processes.
To show chemical non homogeneity in the
distribution of certain constituents
appearing in alloys upon their
solidification from the liquid state.

20
4. Micro-examination requires proper
surface preparation of the specimen before
studying it under the
microscope.
4. Surface preparationfor macro examination
follows similar lines to those for micro
examination but need not be taken to such
a high degrees of surface finish and so
the final stages of polishing can be
omitted.
5. Micro-examination requires that the
polished specimen surface should be etched
with suitable reagent.
5. Macro-examination is also carried out
on an etched surface. Various Etching
Reagents For Steel Nitric acid 25 CC,
Water 75 CC
Steel Grain Size To ASTM E-112
Universally accepted standard by which grain sized range form 1 (very coarse) to 8 (very fine).
Grain size is normally quantified by a numbering system. Coarse 1-5 and fine 5-8.
ASTM E112
Microstructural examination can provide quantitative information about the following
parameters:
1) The grain size of specimens
2) The amount of interfacial area per unit volume
3) The dimensions of constituent phases
4) The amount and distribution of phases

21
Exercise No.-3
Q.-1 Differentiate between Micro and Macro Examination.

22
Q.-2 List the various steps required for the preparation of micro-examivnation .

23
Experiment No.-4
Aim: To identify the different types of material available for design,
manufacturing and processing of various components based on structure
property-performance-processing relationships.
Introduction:
Materials are probably more deep seated in our culture than most of us realize. Transportation,
housing, clothing, communication, recreation, and food production— virtually every segment of our
everyday lives is influenced to one degree or another by materials. Historically, the development
and advancement of societies have been intimately tied to the members’ ability to produce and
manipulate materials to fill their needs. In fact, early civilizations have been designated by the level
of their materials development (Stone Age, Bronze Age, Iron Age).
The earliest humans had access to only a very limited number of materials, those that occur
naturally: stone, wood, clay, skins, and so on. With time, they discovered techniques for producing
materials that had properties superior to those of the natural ones; these new materials included
pottery and various metals. Furthermore, it was discovered that the properties of a material could be
altered by heat treatments and by the addition of other substances. At this point, materials utilization
was totally a selection process that involved deciding from a given, rather limited set of materials,
the one best suited for an application by virtue of its characteristics. It was not until relatively recent
times that scientists came to understand the relationships between the structural elements of
materials and their properties. This knowledge, acquired over approximately the past 100 years, has
empowered them to fashion, to a large degree, the characteristics of materials. Thus, tens of
thousands of different materials have evolved with rather specialized characteristics that meet the
needs of our modern and complex society, including metals, plastics, glasses, and fibers.
The development of many technologies that make our existence so comfortable has been intimately
associated with the accessibility of suitable materials. An advancement in the understanding of a
material type is often the forerunner to the stepwise progression of a technology. For example,
automobiles would not have been possible without the availability of inexpensive steel or some
other comparable substitute. In the contemporary era, sophisticated electronic devices rely on
components that are made from what are called semiconducting materials.
Materials Science and Engineering:
Sometimes it is useful to subdivide the discipline of materials science and engineering into
materials science and materials engineering sub disciplines. Strictly speaking, materials science
involves investigating the relationships that exist between the structures and properties of materials.
In contrast, materials engineering involves, on the basis of these structure–property correlations,
designing or engineering the structure of a material to produce a predetermined set of properties.2
From a functional perspective, the role of a materials scientist is to develop or synthesize new
materials, whereas a materials engineer is called upon to create new products or systems using
existing materials and/or to develop techniques for processing materials. Most graduates in materials
programs are trained to be both materials scientists and materials engineers.

24
Structure is, at this point, a nebulous term that deserves some explanation. In brief, the structure of a
material usually relates to the arrangement of its internal components. Subatomic structure involves
electrons within the individual atoms and interactions with their nuclei. On an atomic level,
structure encompasses the organization of atoms or molecules relative to one another. The next
larger structural realm, which contains large groups of atoms that are normally agglomerated
together, is termed microscopic, meaning that which is subject to direct observation using some type
of microscope. Finally, structural elements that can be viewed with the naked eye are termed
macroscopic.
Virtually all important properties of solid materials may be grouped into six different categories:
mechanical, electrical, thermal, magnetic, optical, and deteriorative. For each, there is a
characteristic type of stimulus capable of provoking different responses. Mechanical properties
relate deformation to an applied load or force; examples include elastic modulus (stiffness),
strength, and toughness. For electrical properties, such as electrical conductivity and dielectric
constant, the stimulus is an electric field. The thermal behavior of solids can be represented in terms
of heat capacity and thermal conductivity. Magnetic properties demonstrate the response of a
material to the application of a magnetic field. For optical properties, the stimulus is electromagnetic
or light radiation; index of refraction and reflectivity are representative optical properties. Finally,
deteriorative characteristics relate to the chemical reactivity of materials.
In addition to structure and properties, two other important components are involved in the science
and engineering of materials—namely, processing and performance. With regard to the relationships
of these four components, the structure of a material depends on how it is processed. Furthermore, a
material’s performance is a function of its properties. Thus, the interrelationship among processing,
structure, properties, and performance is as depicted in the schematic illustration shown in Figure .
Throughout this text, we draw attention to the relationships among these four components in terms
of the design, production, and utilization of materials.
Fig. The four components of the discipline of materials science and engineering and their
interrelationship.
CLASSIFICATION OF MATERIALS:
In this type of classification, engineering material can be classified into two categories: Metals and
non-metals as shown in Figure. Again non-metals are classified into organic & inorganic as shown
in Fig. Metals can be classified into two categories: ferrous and non-ferrous metals. Ferrous metals
contain iron in it. Pure iron has limited use but when alloyed with carbon it has a great commercial
value. Some of the common alloys of iron are steel and cast iron which contain different percentages
of carbon in it. Steel contains 0.02% to 2.11% of carbon and rest iron, manganese, chromium,
nickel, and molybdenum in it. Cast iron contains 2% to 4% of carbon in it and the rest are iron &
silicon.
Non-Ferrous metals contain other metallic elements other than iron in it. They include metals
aluminum, copper, gold etc.

25
Classification of engineering materials in to six broad families.
Classification of engineering materials in two groups
Ceramics are compounds. These compounds contain a metallic and a non-metallic part. The non-
metals can be oxygen, nitrogen and carbon. Examples of ceramics include carbides, clay, silica,
alumina etc.

26
Polymers are compounds which consist of repeating units in them called as “mers”. Mers share
electrons to form very large molecules - usually of carbon and some other elements like oxygen,
hydrogen, nitrogen, chlorine etc. Polymers are further classified into thermosetting, thermoplastics
and elastomers. Some of the common polymers are polythene, PVC, etc.
Classification of organic materials
Composites consist of two or more phases of materials. The phases are processed separately and
then bonded together to achieve properties superior to the constituents. Some of the materials used
in the phases are wood or fiber etc. which are a homogenous mass bonded together with epoxy.
Some of the common applications of composites are aircraft, tennis rackets, car bodies, etc.
Classification of inorganic materials

27
Factors that Govern Material Selection for Engineering Applications
During selection of materials, following factors must be taken into] consideration:
1. Properties of material
 Properties can be defined as response of material to the external stimulation. Properties
can be classified into six categories based upon the type of external stimulations
provided to act upon the material.
 Mechanical properties: Like strength, hardness, toughness.
 Electrical properties: Like resistance, conductance.
 Magnetic properties: Like permeability, magnetic saturation.
 Thermal properties: Like refractoriness.
 Optical properties: Like reflectivity, refractive index
 Chemical properties: Like oxidation, corrosion resistance.
2. Service requirements
 Material selected should not only be suitable for withstanding types and magnitude of
various forces but also must withstand the service environments.
 e.g. material for furnace doors must withstand high temperatures.
3. Reliability
 Reliability is degree of probability that the component and its material retain their
stability in order to serve the function for which it is designed.
 e.g. cheap screw drivers are not reliable as they do not show of reliability in properties
as well as in dimensions.
4. Cost and availability
Abundance i.e. easy availability of materials plays important role in selection of materials for
engineering applications cost is also a major constraint in selection of materials.
5. Safety
Chosen material must perform the function efficiently in the service conditions. Materials
showing catastrophic i.e. brittle failures are almost always avoided as they are serious threat to
the safety.
6. Service environments
Material selection is largely influenced by the environment surrounding the material e.g.-
Sea water machinery asks for special quality materials.
7. Biodegradability and recyclability
 Bio-degradable and recyclable materials are preferred nowadays as they do not affect
ecological balance adversely.
 E-waste, non-biodegradable wastes are serious problems in modern society.

28
Exercise No.-4
Q.-1 Justify the sentence: “Ceramics are hard and brittle.”
Q.-2 Justify the sentence: “Polymers are good insulators.”

29
Q.-3 Justify the sentence: “Glasses are transparent in nature-evaluate.”
Q-4 Explain about an alloy? List out 5 names for ferrous and 5 names for non-ferrous
metals.

30
Experiment No.-5
Aim: To show the effect of different quenching media (Oil, Water and Brine) on
the hardness of medium carbon steel.
Introduction:
The cooling rate of an object depends on many things. The size, composition, and initial
temperature of the part and final properties are the deciding factors in selecting the quenching
medium. A quenching medium must cool the metal at a rate rapid enough to produce the desired
results.
Mass affects quenching in that as the mass increases, the time required for complete cooling also
increases. Even though parts are the same size, those containing holes or recesses cool more rapidly
than solid objects. The composition of the metal determines the maximum cooling rate possible
without the danger of cracking or warping. This critical cooling rate, in turn, influences the choice
of the quenching medium.
The cooling rate of any quenching medium varies with its temperature; therefore, to get uniform
results, you must keep the temperature within prescribed limits. The absorption of heat by the
quenching medium also depends, to a large extent, on the circulation of the quenching medium or
the movement of the part. Agitation of the liquid or the part breaks up the gas that forms an
insulating blanket between the part and the liquid.
Normally, hardening takes place when you quench a metal. The composition of the metal usually
determines the type of quench to use to produce the desired hardness. For example, shallow-
hardened low-alloy and carbon steels require severer quenching than deep-hardened alloy steels that
contain large quantities of nickel, manganese, or other elements. Therefore, shallow-hardening
steels are usually quenched in water or brine, and the deep-hardening steels are quenched in oil.
Sometimes it is necessary to use a combination quench, starting with brine or water and finishing
with oil. In addition to producing the desired hardness, the quench must keep cracking, warping, and
soft spots to a minimum.
The volume of quenching liquid should be large enough to absorb all the heat during a normal
quenching operation without the use of additional cooling. As more metals are quenched, the liquid
absorbs the heat and this temperature rise causes a decrease in the cooling rate. Since quenching
liquids must be maintained within definite temperature ranges, mechanical means are used to keep
the temperature at prescribed levels during continuous operations.
LIQUID QUENCHING
The two methods used for liquid quenching are called still-bath and flush quenching.
Instill-bath quenching, you cool the metal in a tank of liquid. The only movement of the liquid is
that caused by the movement of the hot metal, as it is being quenched.
For flush quenching, the liquid is sprayed onto the surface and into every cavity of the part at the
same time to ensure uniform cooling. Flush quenching is used for parts having recesses or cavities

31
that would not be properly quenched by ordinary methods. That assures a thorough and uniform
quench and reduces the possibilities of distortion.
Quenching liquids must be maintained at uniform temperatures for satisfactory results. That is
particularly true for oil. To keep the liquids at their proper temperature, they are usually circulated
through water-cooled coils. Self-contained coolers are integral parts of large quench tanks.
Fig.-Portable quench tank.
A typical portable quench tank is shown in figure 2-3. This type can be moved as needed to various
parts of the heat-treating shop. Some tanks may have one or more compartments. If one
compartment contains oil and the other water, the partition must be liquid-tight to prevent mixing.
Each compartment has a drain plug, a screen in the bottom to catch scale and other foreign matter,
and a mesh basket to hold the parts. A portable electric pump can be attached to the rim of the tank
to circulate the liquid. This mechanical agitation aids in uniform cooling.
Water
Water can be used to quench some forms of steel, but does not produce good results with tool or
other alloy steels. Water absorbs large quantities of atmospheric gases, and when a hot piece of
metal is quenched, these gases have a tendency to form bubbles on the surface of the metal. These
bubbles tend to collect in holes or recesses and can cause soft spots that later lead to cracking or
warping.
The water in the quench tank should be changed daily or more often if required. The quench tank
should be large enough to hold the part being treated and should have adequate circulation and
temperature control. The temperature of the water should not exceed 65°F.
When aluminum alloys and other nonferrous metals require a liquid quench, you should quench
them in clean water. The volume of water in the quench tank should be large enough to prevent a
temperature rise of more than 20°F during a single quenching operation. For heavy-sectioned parts,
the temperature rise may exceed 20°F, but should be kept as low as possible. For wrought products,
the temperature of the water should be about 65°F and should never exceed 100°F before the piece
enters the liquid.

32
Table 2-4.-Properties and Average Cooling Abilities of Quenching Media
Brine
Brine is the result of dissolving common rock salt in water. This mixture reduces the absorption of
atmospheric gases that, in turn, reduces the amount of bubbles. As a result, brine wets the metal
surface and cools it more rapidly than water. In addition to rapid and uniform cooling, the brine
removes a large percentage of any scale that may be present.
The brine solution should contain from 7% to 10% salt by weight or three-fourths pound of salt for
each gallon of water. The correct temperature range for a brine solution is 65°F to 100°F.
Low-alloy and carbon steels can be quenched in brine solutions; however, the rapid cooling rate of
brine can cause cracking or stress in high-carbon or low-alloy steels that are uneven in cross section.
Because of the corrosive action of salt on nonferrous metals, these metals are no quenched in brine.
Oil
Oil is used to quench high-speed and oil-hardened steels and is preferred for all other steels
provided that the required hardness can be obtained. Practically any type of quenching oil is
obtainable, including the various animal oils, fish oils, vegetable oils, and mineral oils. Oil is classed
as an intermediate quench. It has a slower cooling rate than brine or water and a faster rate than air.
The quenching oil temperature should be kept within a range of 80°F to 150°F. The properties and
average cooling powers of various quenching oils are given in table 2-4.

33
Water usually collects in the bottom of oil tanks but is not harmful in small amounts. In large
quantities it can interfere with the quenching operations; for example, the end of a long piece may
extend into the water at the bottom of the tank and crack as a result of the more rapid cooling.
Nonferrous metals are not routinely quenched in oil unless specifications call for oil quenching.
Caustic Soda
A solution of water and caustic soda, containing 10 percent caustic soda by weight, has a higher
cooling rate than water. Caustic soda is used only for those types of steel that require extremely
rapid cooling and is NEVER used as a quench for nonferrous metals.
This type of quenching uses materials other than liquids. In most cases, this method is used only to
slow the rate of cooling to prevent warping or cracking.
Air
Air quenching is used for cooling some highly alloyed steels. When you use still air, each tool or
part should be placed on a suitable rack so the air can reach all sections of the piece. Parts cooled
with circulated air are placed in the same manner and arranged for uniform cooling. Compressed air
is used to concentrate the cooling on specific areas of a part. The airlines must be free of moisture to
prevent cracking of the metal.
Although nonferrous metals are usually quenched in water, pieces that are too large to fit into the
quench tank can be cooled with forced-air drafts; however, an air quench should be used for
nonferrous metal only when the part will not be subjected to severe corrosion conditions and the
required strength and other physical properties can be developed by a mild quench.
Solids
The solids used for cooling steel parts include cast-iron chips, lime, sand, and ashes. Solids are
generally used to slow the rate of cooling; for example, a cast-iron part can be placed in a lime box
after welding to prevent cracking and warping. All solids must be free of moisture to prevent uneven
cooling.

34
Exercise No.-5
Q.-1 list the various reasons for the formation of cracks, distortion or warpage after
quenching.

35
Q.-2 Explain importance of quenching media on hardness of steel.

36
Experiment No.-6
Aim: To understand the concept of hardenability and its relevance to heat
treatment procedure to be adopted in practice.
Introduction:
Heat treatments are carried out to change the properties of materials by changing the microstructure
of materials. The primary aim of majority of heat treatments is to change the mechanical properties
of the given material; primarily, they are used either to harden (precipitation hardening, quenching,
carburizing, nitriding, etc) or soften (tempering, annealing, stress relieving, etc). Hence, in majority
of cases, the success or failure of heat treatment is decided by the mechanical property
measurements; more specially, hardness is the typical quantity that is measured.
Hardness is the resistance of a material to plastic deformation. It also correlates with the other
mechanical properties such as strength (direct) and ductility (inverse). Further, hardness tests are
easy to perform, and, if needed, can be performed without having to discard the sample after testing.
This is the reason why hardness tests are usually employed after heat treatment processes.
Hardenability is the ability for a material to harden; it refers not to the highest value of hardness that
can be obtained but to the capacity (depth or thickness over which such high hardness values can be
achieved) to harden. Thus, hardenability is intimately related to the cooling rate that can be achieved
(especially in steels). Typically, hardenability is tested using hardness penetration diagram test (in
which, the hardness of a hardened sample is plotted as a function of depth from the surface), and
Jominy end quench test (in which one end of a sample is quenched and the hardness at equal
intervals from the quenched end is measured and plotted).
Hardening Temperatures and Soaking Time
Austenitizing temperature prior to hardening depends upon the carbon content of the steel.
Hypoeuctectoid steels are heated to complete austenitic phase, while hypereutectoid steels are
heated to obtain a phase mixture of austenite and cementite.
The austentizing temperature is determined as follows:
Hypoeuctectoid steels—Ac3 + 50°C
Hypereuctectoid steels—Ac1 + 50°C
These temperature are generally unaffected by the presence of small amount of alloying elements.
Care must be taken to obtain temperature uniformity through the entire cross section and not to
exceed the recommended temperatures. Optimum hardening temperatures for different carbon steels
are given in table. After reaching the austenizing temperature, steel is held at this temperature at the
rate of 1 hour/25 mm thickness.

37
Microstructure and properties after hardening
When steel is quenched from the austenitizing temperature, austenite is transformed to martensite.
This transformation of austenite to martensite is temperature dependent, and some amount of
austenite remains untransformed even at room temperature. The untransformed austenite is called
retained austenite. Retained austenite is always present in steels after quenching, unless steel has
been quenched at subzero temperature.
In addition to martensite and retained austenite, hardened steel may contain carbides which were not
dissolved in austenite during austenitizing. Therefore, microstructure of hardened steel may consist
of martensite, retained austenite and carbides.
The hardness of steel after quenching depends upon the hardness of martensite. Hardness of
martensite is a function of its carbon content. It increases with increase in carbon content and attain
the saturation at carbon content of about 0.6 percent.
Variable Affecting Hardening of Steel
The process of hardening of steel is widely used in industry. Most of engineering components are
hardened and tempered before they are put in service. The hardening process of steel looks to be
very simple. It requires heating the steel to austenitizing temperature and then quenching it in a
liquid bath. But it may not give you the expected hardness in steel. The reason is, that the kinetics of
formation of martensite is very complicated, and is greatly affected by a large number of variables
which may reduce the hardness to an appreciable extent.
Some of these variables are austenitizing temperature, holding time, type and temperature of
quenching medium, mass and size of the object.
Jominey End Quench Test:
Hardenability
 When a steel piece of large cross section is heated to a austenite temperature and then
quenched, the cooling rate decreases from the surface to the interior. Martensite is
obtained at the surface due to highest cooling rate. But it is not possible to get a
martensitic structure at the center due to the relatively slow cooling rate. Hence, a
gradient of hardness exists from the surface to the center. Since every grade of steel has its
own transformation characteristics, the depth of penetration of hardness across the cross
section differs. The measure of these properties termed as Hardenability of the steel.

38
 Hardenability is defined as the relative ability of steel to be hardened by quenching and it
determines the depth and distribution of hardness across the cross section.
Hardenability should not be confused with maximum hardness of steel.
 Hardenability is very useful and important property of steel. It determines the rate at
which the given steel should be quenched. Maximum hardness is mainly a function of
carbon content. Hardenability of steel depends on
1. Composition of steel
2. Method of manufacture
3. Section of the steel
4. Quenching medium
5. Quenching method
In industry, a simple experiment called Jominey End Quench Test (named after Walter
Jominey, American Metallurgist) is used to determine Hardenability of steel.
Objectives:
The objective of the experiment is to take readings in the Rockwell C scale along the flat
surface of the Jominey specimen and to plot the graph Hardness vs. Distance from
quenched end.
Equipment:
1. Electric furnace
2. Jominey end quench test fixture
3. Jominey specimen (made as per ASTM standard)
4. Rockwell hardness tester
Test Procedure:
1. Preheat the furnace to 1700° F (910°C-920° C)
2. Place the Jominey specimen in the furnace and soak for one hour.
3. Turn the water on at Jominey sink. Adjust the free water column about 2.5 inches.
Swivel the baffle plate to block the water column so that there is no contact between
water and the test specimen when the test specimen is initially placed on the fixture.
4. Remove the Jominey specimen from the furnace and place in the fixture as shown in figure.
Swivel the baffle out of position so that water impinges on the bottom of the specimen without
wetting the sides of specimen. Leave water running for about 15 minutes.

39
Fig. Apparatus used in the test and Standard form of test piece
5. Remove the Jominey specimen from the fixture and grind a flat on the side of the
specimen.
6. Mark points on the ground surface at an interval of 1.6mm distance from the quench
end as shown in figure.
7. Take reading at an interval of 1.6mm intervals. Near the quenched end, this interval is
reduced to 0.8mm as hardness values vary rapidly.

40
Exercise No.-6
Q.-1 Explain about hardenability. List out the factors on which hardenability depends.

41
Q.-2 Differentiate between hardness and hardenability. How is hardenability useful?

42
Experiment No.-7
Aim: To find out the effect of varying section size on hardenability of steel and
obtain hardness distribution curves of hardened steel cross-section.
Introduction:
The hardenability of a steel is defined as that property which determines the depth and Distribution
of hardness induced by quenching ftom the austenitic condition. The dependence of hardness upon
quenching rate can be understood ftom the time-temperature-transformation characteristics of steel,
and, for a particular steel, can be estimated from the T-T-T diagram. A part may be hardened by
quenching into water, oil, or other suitable medium. The surface of the part is cooled rapidly,
resulting in high hardness, whereas the interior cools more slowly and is not hardened. Because of
the nature of the T-T-T diagram, the hardness does not vary linearly from the outside to the center.
Hardenability refers to capacity of hardening (depth) rather than to maximum attainable hardness.
The hardenability of a steel depends on
(1) The composition of the steel,
(2) The austenitic grain size, and
(3) The structure of the steel before quenching.
In general, hardenability increases with carbon content and with alloy content. The most
Important factor influencing the maximum hardness that can be obtained is mass of the metal being
quenched. In a small section, the heat is extracted quickly, thus exceeding the critical cooling rate of
the specific steel and this part would thus be completely martensitic. The critical cooling rate is that
rate of cooling which must be exceeded to prevent formation of non martensite products. As section
size increases, it becomes increasingly difficult to extract the heat fast enough to exceed the critical
cooling rate and thus avoid formation of non-martensitic products. Hardenability of all steels is
directly related to critical cooling rates.
Procedure:
Sample of medium carbon steel machined to the shape shown in Fig.2. It is a cylindirical bar with a
25 mm. diameter and 100 mm. length. The specimen is placed in the furnace at 900 0C for about 1/2
hour. The water flow rate is adjusted so that the water column is approximately the distance 50 mm
above the end of the pipe, when water is flowing freely. After the sample has been austenitized, it is
removed from the furnace and placed directly into the quenching apparatus. A jet of water is quickly

43
splashed at one end of the specimen. After the entire sample has cooled to room temperature, the
scale oxidation is removed; two opposite and flat parallel surfaces are ground along the length of the
bar. Rockwell C hardness measurements are then made every 2 mm and these readings are recorded.
Photograph of Jominy specimen cooling forming water umbrella

44
Jominy test set up
RESULTS
When a small specimen (up to 20mm in thickness) is austenitized and quenched in a liquid bath, the
expected hardness values may be obtained by the rapid cooling of the specimen by the liquid. But as
the mass and size of the object increases, the cooling rate at the surface and at the interior of the
object decreases, because a large quantity of the heat per unit surface area of the object is to be
removed by the liquid. It takes a longer time to achieve the same temperature at the face of a large
object than for a small specimen. During this larger duration of time, austenite may transform to
other products, such as pearlite, and hence hardness decreases. The effect of the bar diameter on the
resulting hardness of a 0.5% carbon steel after hardening is shown in table. The table shows that
0.5% carbon steel bar of 150 mm diameter will develop a hardness of 21 Rc only, even after water
quenching.

45
Exercise No.-7
Q.-1 Explain the importance of section size on hardness and hardenability of given steel.

47
Q.-2 Explain detail of components on simple double acting cylinder with neat line sketch and
state the function of each component.

48
Experiment No.-8
Aim: Study of different heat treatment processes- annealing, normalizing,
hardening and tempering, surface and casehardening to improve properties of
steel during processes and applications.
Introduction:
Heat treatment is the process of heating (but never allowing the metal to reach the molten state) and
cooling a metal in a series of specific operations which changes or restores its mechanical
properties.
Heat treatment makes a metal more useful by making it stronger and more resistant to impact, or
alternatively, making it more malleable and ductile. However, no heat-treating procedure can
produce all of these characteristics in one operation; some properties are improved at the expense of
others. For example, hardening a metal may make it brittle, or annealing it may make it too soft.
Stages of heat treatment:
heat treatment in three major stages:
• Stage l — Heat the metal slowly to ensure a uniform temperature.
• Stage 2 — Soak (hold) the metal at a given temperature for a given time.
• Stage 3 — Cool the metal to room temperature.
There are four basic types of heat treatment in use today: annealing, normalizing, hardening,
tempering and case hardening.
Annealing :
Annealing consists of heating a metal to a specific temperature and then cooling at a rate that will
produce a refined microstructure, either fully or partially separating the constituents. The rate of
cooling is generally slow. Annealing is most often used to soften a metal for cold working, to
improve machinability, or to enhance properties like electrical conductivity.
Fig. Annealing Process

49
In ferrous alloys, annealing is usually accomplished by heating the metal beyond the upper critical
temperature and then cooling very slowly, resulting in the formation of pearlite. In both pure metals
and many alloys that cannot be heat treated, annealing is used to remove the hardness caused by
cold working. The metal is heated to a temperature where recrystallization can occur, thereby
repairing the defects caused by plastic deformation. In these metals, the rate of cooling will usually
have little effect. Most non-ferrous alloys that are heat-treatable are also annealed to relieve the
hardness of cold working. These may be slowly cooled to allow full precipitation of the constituents
and produce a refined microstructure.
Ferrous alloys are usually either "full annealed" or "process annealed." Full annealing requires very
slow cooling rates, in order to form coarse pearlite. In process annealing, the cooling rate may be
faster; up to, and including normalizing. The main goal of process annealing is to produce a uniform
microstructure. Non-ferrous alloys are often subjected to a variety of annealing techniques,
including "recrystallization annealing," "partial annealing," "full annealing," and "final annealing."
Not all annealing techniques involve recrystallization, such as stress relieving.
Normalizing:
Fig. Normalizing Process
Normalizing is a technique used to provide uniformity in grain size and composition (equiaxing)
throughout an alloy. The term is often used for ferrous alloys that have been austenized and then
cooled in open air. Normalizing not only produces pearlite, but also martensite and sometimes
bainite, which gives harder and stronger steel, but with less ductility for the same composition than
full annealing.
Stress relieving:
Stress relieving is a technique to remove or reduce the internal stresses created in a metal. These
stresses may be caused in a number of ways, ranging from cold working to non-uniform cooling.
Stress relieving is usually accomplished by heating a metal below the lower critical temperature and

50
then cooling uniformly. Stress relieving is commonly used on items like air tanks, boilers and other
pressure vessels, to remove all stresses created during the welding process.
Tempering:
Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A
method for alleviating this problem is called tempering. Most applications require that quenched
parts be tempered. Tempering consists of heating steel below the lower critical temperature, (often
from 400 to 1105 ˚F or 205 to 595 ˚C, depending on the desired results), to impart some toughness.
Higher tempering temperatures (may be up to 1,300 ˚F or 700 ˚C, depending on the alloy and
application) are sometimes used to impart further ductility, although some yield strength is lost.
Tempering may also be performed on normalized steels. Other methods of tempering consist of
quenching to a specific temperature, which is above the martensite start temperature, and then
holding it there until pure bainite can form or internal stresses can be relieved. These include
austempering and martempering.
Case-hardening or surface hardening:
Case-hardening or surface hardening is the process of hardening the surface of a metal object while
allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal
(called the "case") at the surface. For iron or steel with low carbon content, which has poor to no
hardenability of its own, the case-hardening process involves infusing additional carbon or nitrogen
into the surface layer. Case-hardening is usually done after the part has been formed into its final
shape, but can also be done to increase the hardening element content of bars to be used in a pattern
welding or similar process.
Hardening is desirable for metal components that are subject to sliding contact with hard or abrasive
materials, as the hardened metal is more resistant to surface wear. However, because hardened metal
is usually more brittle than softer metal, through-hardening (that is, hardening the metal uniformly
throughout the piece) is not always a suitable choice. In such circumstances, case-hardening can
produce a component that will not fracture (because of the soft core that can absorb stresses without
cracking), but also provides adequate wear resistance on the hardened surface.
Carburizing:
Carburizing is a process used to case-harden steel with a carbon content between 0.1 and 0.3 wt% C.
In this process steel is introduced to a carbon rich environment and elevated temperatures for a
certain amount of time, and then quenched so that the carbon is locked in the structure; one of the
simpler procedures is repeatedly to heat a part with an acetylene torch set with a fuel-rich flame and
quench it in a carbon-rich fluid such as oil.
Carburization is a diffusion-controlled process, so the longer the steel is held in the carbon-rich
environment the greater the carbon penetration will be and the higher the carbon content. The
carburized section will have a carbon content high enough that it can be hardened again through
flame or induction hardening.
It is possible to carburize only a portion of a part, either by protecting the rest by a process such as
copper plating, or by applying a carburizing medium to only a section of the part.

51
The carbon can come from a solid, liquid or gaseous source; if it comes from a solid source the
process is called pack carburizing. Packing low carbon steel parts with a carbonaceous material and
heating for some time diffuses carbon into the outer layers. A heating period of a few hours might
form a high-carbon layer about one millimeter thick.
Liquid carburizing involves placing parts in a bath of a molten carbon-containing material, often a
metal cyanide; gas carburizing involves placing the parts in a furnace maintained with a methane-
rich interior.
Nitriding:
Nitriding heats the steel part to 482–621 °C (900–1,150 °F) in an atmosphere of ammonia gas and
dissociated ammonia. The time the part spends in this environment dictates the depth of the case.
The hardness is achieved by the formation of nitrides. Nitride forming elements must be present for
this method to work; these elements include chromium, molybdenum, and aluminum. The
advantage of this process is that it causes little distortion, so the part can be case-hardened after
being quenched, tempered and machined. No quenching is done after nitriding.
Cyaniding:
Cyaniding is a case-hardening process that is fast and efficient; it is mainly used on low-carbon
steels. The part is heated to 871–954 °C (1600–1750 °F) in a bath of sodium cyanide and then is
quenched and rinsed, in water or oil, to remove any residual cyanide.
2NaCN + O2 → 2NaCNO
2NaCNO + O2 → Na2CO3 + CO + N2
2CO → CO2 + C
This process produces a thin, hard shell (between 0.25 and 0.75 mm, 0.01 and 0.03 inches) that is
harder than the one produced by carburizing, and can be completed in 20 to 30 minutes compared to
several hours so the parts have less opportunity to become distorted. It is typically used on small
parts such as bolts, nuts, screws and small gears. The major drawback of cyaniding is that cyanide
salts are poisonous.
Flame hardening:
Fig. Flame Hardening

52
Flame hardening is used to harden only a portion of a metal. Unlike differential hardening, where
the entire piece is heated and then cooled at different rates, in flame hardening, only a portion of the
metal is heated before quenching. This is usually easier than differential hardening, but often
produces an extremely brittle zone between the heated metal and the unheated metal, as cooling at
the edge of this heat-affected zone is extremely rapid.
Induction hardening:
Fig. Induction hardening
Induction hardening is a surface hardening technique in which the surface of the metal is heated
very quickly, using a no-contact method of induction heating. The alloy is then quenched, producing
a martensite transformation at the surface while leaving the underlying metal unchanged. This
creates a very hard, wear resistant surface while maintaining the proper toughness in the majority of
the object. Crankshaft journals are a good example of an induction hardened surface.

53
Exercise No.-8
Review Questions (Select the Correct Response)
1. What process consists of tempering, normalizing, hardening, and annealing?
A. Cold forming of metals
B. Heat treatment of nonferrous metals
C. Heat treatment of ferrous metal
D. Quenching of austenitic materials
2. (True or False) Most nonferrous metals can be normalized and case hardened
but not annealed.
A. True
B. False
3. Which of the following conditions is required for the successful heat treatment of
metals?
A. Proper size of furnace
B. Proper furnace atmosphere
C. Suitable quenching medium
D. All of the above
4. What type of furnace produces an atmosphere consisting of a gas/air combustion
product?
A. Oil-fired only
B. Both gas-fired and electric
C. Both oil-fired and gas-fired
D. Both oil-fired and electric
5. Which of these gas mixtures are constituents of a fuel-fired furnace atmosphere?
A. Carbon dioxide, hydrogen, oxygen, and nitrogen
B. Carbon monoxide, nitrogen, argon, and radon
C. Hydrogen, bromine, oxygen, and chlorine
D. Hydrogen, oxygen, argon, and radon
6. What allows you to provide an oxidizing, reducing, or neutral atmosphere in a fuel fired furnace?
A. Varying the type of fuel
B. Construction of the furnace
C. Varying the proportion of air to fuel
D. All of the above
7. What type of furnace(s) allows the atmosphere to consist of air only?
A. Oil-fired
B. Electric
C. Both oil-fired and gas-fired
D. Both oil-fired and electric
8. What is the primary cause of distortion and cracking of the heat-treated part?
A. Heating the part too slowly
B. Increasing the soaking temperature too slowly
C. Uneven expansion due to carbon deposits in the part
D. Heating one section of the part more rapidly than other parts

54
9. How do you determine the soaking period when parts are uneven in cross section?
A. By the total weight
B. By the largest section
C. By the lightest section
D. By the number of parts
10. What type of medium is normally used to quench nonferrous metals?
A. Oil
B. Brine
C. Air
D. Water
11. What effect is produced when steel is cooled very slowly in a medium that does NOT conduct
heat easily?
A. Maximum softness
B. Maximum hardness
C. Maximum ductility
D. Minimum ductility
12. Copper becomes hard and brittle when mechanically worked, but it can be made soft again by
annealing. Within what temperature range must you heat it to anneal it?
A. 500°F to 600°F
B. 600°F to 700°F
C. 700°F to 900°F
D. 900°F to 1100°F
13. (True or False) Normalizing is a form of heat treatment applicable to nonferrous metals only.
A. True
B. False
14. Which of these metals are difficult to harden by heat treatment?
A. Wrought irons
B. Pure irons
C. Extremely low-carbon steels
D. All of the above
15. What factor almost completely determines the maximum obtainable hardness in plain carbon
steel?
A. The carbon content of the steel
B. The thickness of the steel
C. The heating time
D. The temperature to which it was heated
16. What case-hardening method produces the hardest surface of any of the hardening processes?
A. Nitriding
B. Cyaniding
C. Carburizing
D. Halogenizing
17. If the steel parts are placed in a container packed with charcoal and heated in a furnace, what
case-hardening process is being used?
A. Cementation

55
B. Pack hardening
C. Carburizing
D. Atmospheric cementation
18. On what areas of a part being flame hardened should a slightly oxidizing flame be used?
A. Flat surfaces
B. Corners and grooves
C. Rounded surfaces
D. Edges and elongated sections
19. Which of these factors determines the rate at which you move the welding torch when flame
hardening a steel part?
A. Mass of the part
B. Shape of the part
C. Depth of the hardness desired
D. All of the above
20. (True or False) Flame hardening can produce a hard case that resists wear while the core retains
the metal’s original properties.
A. True
B. False
21. What term is used to describe the process of heating steel to a specific temperature (below its
hardening temperature), holding this temperature for a certain length of time, and then cooling the
steel in still air to room temperature?
A. Annealing
B. Hardening
C. Tempering
D. Case hardening
22. (True or False) Steel can be tempered provided some hardness remains after it has been
normalized.
A. True
B. False
23. In which of the following metals are the softness, ductility, and resistance to impact NOT
increased?
A. Aluminum
B. High-speed steel
C. Low-carbon steel
D. Already hardened steel
24. What are the most important properties to be obtained in tempering permanent steel magnets?
A. Stability and malleability
B. Softness and malleability
C. Hardness and stability
D. Ductility and resistance to wear
25. Why should you agitate the part or the quenching medium when cooling a part?
A. To break up gases that form
B. To induce oxidation
C. To reduce the cooling rate
D. To raise the temperature of the liquid

56
Experiment No.-9
Aim: To understand the procedure of testing, nature of indication, the
capability and sensitivity of the liquid penetrant test and the magnetic particle
test.
Introduction:
LIQUID PENETRANT TEST:
A liquid penetration test is non-destructive type. It defects flaws that are open to the surface e.g.
cracks, seams, laps, lack of bond, porosity, cold shuts, etc. It can be effectively used not only in the
inspection of ferrous metals but is especially useful for non-ferrous metals products and on non-
porous, non-metallic material such as ceramics, plastics and glass.
Principle:
The principle of liquid penetrant test is that the liquids used either small opening such as crack or
porosities by capillary action. The rate and extent of this action are dependent upon such properties
as surface tension, cohesion, adhesion and viscosity. They are also influenced by factor such as the
condition of the surface of material and the interior of the discontinuity.
For the liquid to penetrate effectively, the surface of the material must be thoroughly cleaned of all
material that would obstruct the entrance of the liquid into the defect.
After cleaning, the liquid penetrate is applied evenly over the surface and allowed to remain long
enough to permit penetration into possible discontinuities
The liquid is then completely removed from the surface of the component and either a wet or a dry
developer is applied. The liquid that has penetrated the defect will then bleed out into the surface
and developer will help delineate then.
This will show the location and general nature and magnitude of any defect present. To hasten this
action, the part may be struck sharply to produce vibration to force the liquid out of the defect.
OIL- WHITING TEST: It is one of the older and cruder penetrant tests used for the detection of
cracks too small to be noticed in a visual inspection. In this method, the piece is covered with
penetrating oil, such as kerosene, then rubbed dry and coated with dry whiting. In a short time the
oil has seeped into any cracks will be partially absorbed by the whiting, producing plainly visible
discolored streaks delineating the cracks.

57
DYE PENETRANT TEST: It is based on liquid penetrants is a sensitive extremely versatile and a
very reliable method of test. It is quite inexpensive, does not require any special apparatus and is
quite simple in application. Only a moderate skill is required.
In this test, the strongly colored red penetrant fluid (or dye) has a property of seeping into surface
flaws when applied on an impervious surface.
The steps involved in liquid penetrant test are:
1. Clean the surface of the component free of dust and dirt with a piece of cloth.
2. Brush the surface of component to remove scale, rust, paint etc. by a soft wire brush.
3. Spray the cleaner to remove oil, grease, etc.
4. Apply the dye penetrant ( by spraying) adequately to cover the area to be tested. Allow 3 to 5
minutes or more for dye to penetrate into the cracks.
5. Wipe off the excess penetrant on the surface with a rag.
6. Again spray the surface with the cleaner to remove the remnants of the red dye.
7. Spray the developer evenly on the surface to give a thin even layer. This layer absorbs the
penetrant from the cracks and red spots or lines appear on the surface to give a visible
indication of the flaws
8. The crack if any will be indicated with the red dye absorbed by the white absorbent
Fig. Liquid penetrant Testing

58
MAGNETIC PARTICLE TEST:
Introduction:
 This method of non-destructive testing tends to supplement rather than displace radiography.
For example, radiography ordinarily cannot detect small cracks, especially when they are too
small to be seen with the human eyes.
 This method of inspection is used in magnetic ferrous castings for detecting invisible surface
or slightly subsurface defects. Deeper subsurface defects are not satisfactorily detected
because the influence of the distorted lines of magnetic flux on the magnetic particles spread
over the casting surface becomes weaker with the distance, so that sensitivity falls away with
the depth.
 The defects commonly revealed by magnetic particle inspection are quenching cracks,
thermal cracks, seams, laps, grinding cracks, overlaps, non-metallic inclusions, fatigue
cracks, hot tears, etc.
 Magnetic particle inspection is a relatively simple and easy technique. It is almost free from
any restriction as to size, shape, composition and heat treatment of ferromagnetic specimen.
Principle of the Method:
When the piece of metal is placed in a magnetic field and the lines of magnetic flux get intersected
by a discontinuity such as crack or slag inclusion in a casting, magnetic poles are induced on either
side of the discontinuity. The discontinuity causes as either side of the discontinuity. The
discontinuity causes an abrupt change in the path of magnetic flux flowing through the casting
normal to the discontinuity, resulting a local flux leakage field and interference with the magnetic
lines of force. This local flux disturbance can be detected by its affect upon magnetic particles
which collect on the region of discontinuity and pile up and bridge over the discontinuity.
A surface crack is indicated by a line of fine particles following the crack outline and a subsurface
defect by a fuzzy collection of the magnetic particles on the surface near the discontinuity.
Maximum sensitivity of indication is obtained when the discontinuity lies in a direction normal to
the applied magnetic field and when the strength of magnetic field is just enough to saturate the
section being inspected.
Procedure:
a) Magnetizing the component part, (e.g., a casting)
b) Applying magnetic particles on the component part.

59
c) Locating the defects.
Figure below shows magnetic flux fields in a magnetized bar containing
a) Surface discontinuity
b) Subsurface discontinuity
Figure: 1) Indication of a crack in slow 2) Indication of cracks in weldamant
3) Before and after inspection pictures of cracks emanating from a hole
In magnetized bar or casting if a crack or void interrupts a magnetic field, the magnetic field get
distorted. The magnetic permeability of air being too low in comparison with iron, the magnetic flux
spreads out to get around the void. Some of the magnetic flux lines extend outside of the metal in
the oar over the discontinuity is noticed or located over the discontinuity and the discontinuity is
noticed or located distinctly because the magnetic particles collect and pile at any discontinuity or
crack.

60
Exercise No.-9
Q.-1 Explain about requirement of developer in LPT.

61
Q.-2 List the capabilities and limitations of LPT.

62
Q.-3 List the basic elements of MPT.
Q.-4 Describe the process of MPT for specific component.

64
Experiment No.-10
Aim: To understand the procedure of testing, nature of indication, the
capability and sensitivity of the Eddy current test and the Ultrasound test.
(A) Ultrasonic Testing:
1. It is used to detect and locate defects such as shrinkage, cavities, cracks, porosity and large
metallic inclusions wall thickness can be measured in close vessel.
2. Ultrasonic vibrations can be used to locate defects in ferrous and nonferrous metals, plastics and
ceramics.
3. Ultrasonic inspection for flow detection makes use of acoustic waves with frequency in the
range of 20 KHz and 20 MHz which can be transmitted through solids and get reflected by
subsurface defects.
4. The use of sound waves to determine a defect is a very old / ancient method. If a piece of metal is
struck by a hammer it will radiate certain audible/easy to hear notes, of which pitch and clamping
may be influenced by the presence of internal flows. However this technique of hammering and
listening is useful only for the determination of large defects.
5. Here sound waves above audible range with frequency 1 to 5 million Hz (cycle/sec) – hence it is
known as ultrasonic.
6. Ultrasonic is a fast, reliable, non-destructive testing method which employs electronically
produced high frequency sound waves that will penetrate metals, liquids and other metals at a speed
of several thousand feet/sec.
7. Ultrasonic waves for NDT are usually produced by piezoelectric materials. These materials
undergo a change in physical dimensions when subjected to electric field.
8. This conversion of electrical energy to mechanical energy is known as “piezoelectric effect”. If an
alternating electric field is applied to a piezoelectric crystal, the crystal will expand during the first
half of cycle and contact when the electric field is reversed. By varying the frequency of the
alternating electric field, we can vary the frequency of the mechanical vibration (sound wave)
produced in the crystal. Quartz is a widely used ultrasonic transducer. A transducer is a device for
converting one form of energy to another.
Fig. Detection of crack with ultrasonic Machine.

65
Fig. Ultrasonic inspection
1. Through Transmission Method:
This method uses an ultrasonic transducer on each side of the object being inspected. If an
electrical pulse of the desired frequency is applied to the transmitting crystal, the ultrasonic waves
produced will travel through the specimen to the other side. The receiving transducer on the
opposite side receive the vibrations and converts them in to an electrical signed than can be
amplified and observed on the cathode ray tube of an oscilloscope, a meter or some other
indicator. If the ultrasonic wave travels through the specimen without encountering any flow,
the signal received is relatively large. If there is a flow in the path of the ultrasonic wave part of
the energy will be reflected and the signal received by the receiving transducer will be reduced.
2. The Pulse Echo Method:
 This method uses one transducer which serves as both transmitter and receiver. It is same
as the transmission method.
 As sound wave enters the material being tested, part of it is reflected back to the crystal where
it is converted back to an electrical impulse.
 This impulse is amplified and rendered visible as an indication or pip on the screen of the
oscilloscope. When the sound wave reached the other side of the material, it is reflected back
and shows a pip on the screen further to the right of first pip. If there is a flow between
front and back surface of the material, it will shows as a third pip on the screen between the
two indications for the front and back surfaces.
 Since the indications on the oscilloscope screen measure the elapsed time between
reflection of the pulse from the front and back surfaces, the distance between
indications is a measure of the thickness of the material. The location of a defect may
therefore be accurately determined from the indications on the screen.
For larger parts, a film of oil ensured proper contact between the crystal searching unit and
test piece. Smaller parts may be placed in a tank of water, oil or glycerin. The crystal searching
units transmits sound waves through the medium and into material being examined.

66
 Close examination of the oscilloscope screen in the picture shows the presence of three pips.
The left pip indicates the front of the piece. The right pip the back of the piece and the smaller
center pip is an indication of flow.
Applications:
1. It is used to detect and locate such defect as shrinkage cavities, internal bursts or cracks,
porosity and large non- metallic inclusions.
2. Wall thickness can be measured in a close vessel.
Couplant (oil glycerin base substance) is used to help make contact between the transducer & the
surface of material. It performs the function of removing air from in-between of a medium for
proper transfer of sound vibrations.
It major applications are:
Mill components Rolls, shafts & drive press columns, Power equipment Turbine, forging generator
rotor, Jet engine parts Turbine & compressor forging, casting components Aircraft components.
Inspection
method
When to use Where to use Advantages Limitations
Ultrasonic
pulse echo
Finding
internal
defects,
cracks, lack
of bond,
laminations,
porosity,
determining
grain
structure and
thicknesses.
All metals and
hard nonmetallic
materials, sheets,
tubing, rods,
forgings, castings,
field and
production testing;
in service part
testing; brazed and
adhesive bonded
joints.
Fast, dependable,
easy to operate;
lends itself to
automation,
result of test
immediately
known; relatively
portable, highly
accurate,
sensitive.
Requires
contact or
immersion of
part;
interpretation
of readings
requires
training.

67
(B) Eddy Current Testing:
Principle:
Eddy current inspection is based on the principles of electromagnetic induction and is used to
identify or differentiate between a wide variety of physical, structure and metallurgical conditions in
electrically conductive ferro-magnetic and non-ferromagnetic metals.
Procedure:
In eddy current testing, a varying magnetic field is produced, if a source of a source of
alternating current is connected to a coil. When this field is placed near a test specimen
capable of conducting an electrical current, eddy currents will be induced in the
specimen. The eddy currents, in turn, will produce a magnetic field of their own. The
detection unit will measure this new magnetic field and convert the signal into a voltage that
can read on a meter or a cathode –ray tube. Properties such as hardness, alloy composition,
chemical purity, and heat treat condition influence the magnetic field and may be measured
directly by a single coil.
Fig. Development of Eddy current

68
The part to be inspected is placed within or adjacent to an electric coil in which an alternating
current is flowing. This alternating current causes eddy-current to flow in the part as a result of
electromagnetic induction. The flow of eddy currents in the part depends on the electrical;
characteristics of the part, the presence or absence of flaws or other discontinuities in the part.
The change in flow of eddy-currents caused by the presence of a crack in a pipe as shown in fig. In
section A-A, no crack is present and eddy current flow is symmetrical. In section B-B, where a
crack is present, the eddy-current flow is impeded and changed in direction, causing significant
changes in the associated electromagnetic field. The electromagnetic field surrounding a part
depends partly on the properties and characteristics of the part. Electrical conductivity of the metal
plays an important role for eddy-current response. The conductivity of metal is greatly affected by
the composition, heat treatment, microstructure, grain size, hardness and residual stresses.
In the case of ferromagnetic materials, eddy current passing through the material result in the
magnetization in the part to be tested. The magnetization can be measured easily and will have a
greater response to the change in the structure and properties of the material.
The frequency of the alternating current used in eddy-current inspection ranges from 200 Hertz (Hz)
to 6 x 106
Hz. Most inspection of non-magnetic materials is performed at a few kilohertz. In general,
lower frequencies are used for magnetic materials.
 Eddy- current method can be used for the following purposes:
(i) To measure or identify such conditions and properties as electrical conductivity,
magnetic permeability, grain size, heat treatment condition, hardness and physical
conditions.
(ii) To detect seams, laps, cracks, voids and inclusions.
(iii) To sort dissimilar metals and detect differences in their composition, microstructure
and other properties.
(iv) To measure coating thickness.
Because eddy-current inspection is an electromagnetic induction technique, it does not require direct
electrical contact with the part being inspected. The method is adaptable to high speed inspection
and can be used to inspect an entire production output if desired.
Inspection
method
When to use Where to use Advantages Limitations
Eddy current Measuring variations
in wall thickness of
thin metals or
coatings; detecting
longitudinal seems or
cracks in tubing;
determining heat
treatments and metal
compositions for
sorting.
Tubing and
bar stock,
parts of
uniform
geometry,
flat stock, or
sheet and
wire.
High speed,
noncontact,
automatic.
False indication
result from
many variables;
only good for
conductive
materials;
limited depth of
penetration.

69
Exercise No.-10
Q.-1 Explain the working principal of ultrasonic test.

70
Q.-2 Explain 5 basic elements for ultrasonic testing.
Q.-3 List 3 specific applications for ultrasonic testing.

71
Q.-4 State the factors affecting eddy current. And explain any two of them.

72
Q.-5 List various application of eddy current test.

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