RAJIV GANDHI
DEPT. OF MECHANICAL ENGG.
COLLEGE OF ENGINEERING, RESEARCH & TECHNOLOGY;
CHANDRAPUR - 03
B.E. ( MECH ) – III SEM.
SUB – ENGINEERING METALLURGY
LIST OF PRACTICALS
( 2004 – 05 )
1.
Study of crystal structure
2.
Study of metallurgical Microscope
3.
Specimen Preparation
4.
Metallography ( Study & drawing of microstructure ) of plain carbon
steel (A1, A2, A3 ) ( A4, A5, A6)
5.
Metallography of cast iron (B1, B2, B3, B4)
6.
Metallography of non-ferrous metals.
(C1, C2, C3 ) ( C4, C5, C6 ) (C7, D1, F1)
7.
Metallography of heat-treated specimen.
(E1, E2, E3) ( E4 , E5, E6, E7) ( D2, D3, F2, F3 )
8.
Hardness Test By i) Brinnel
9.
Impact Test
10. Tensile test.
ii) Rockwell test.
EXP NO. 1
AIM : STUDY OF CRYSTAL STRUCTURE OF METALS.
Solid can be divided in to two types i.e. crystalline and amorphous. Crystalline material shows periodic
arrangement of atoms
& consists of unit cells. All metals, many ceramics, some plastics & most
minerals are crystalline. In the amorphous material, the atoms are arranged in random manner. It is necessary
to study the crystal structure, since all metals & alloys are crystalline in nature.
UNIT CELL :
It is smallest regular shape, which
when repeated , generates the whole crystal lattice. It is
specified by three vectors a , b , c and
opposite to
three angles
them α , β , γ . Unit cell is fundamental
building block of the crystal. With the help of mathematical
calculations, French scientist AUGUSTE BRAVAIS has
shown that by varying the conditions, 7 systems & 14
FIG 1. UNIT CELL
lattices are possible. They are named after him & are popularly referred as BRAVAIS LATTICES.
SYSTEM
CONDITIONS
LATTICES
1) CUBIC
a=b=c &
α = β = ϒ = 90°
a) Simple cubic
b) Face centered cubic
c) Body centered cubic
2) TETRAGONAL
a=b#c &
α = β = ϒ = 90°
a) Simple Tetragonal
b) Body centered tetragonal
a#b#c &
α = β =ϒ = 90
a) Simple Orthorhombic
b) Body centered Orthorhombic
c) Face centered Orthorhombic
d)Base centered Orthorhombic
4) RHOMBOHEDRAL
a=b=c&
α = β = ϒ # 90
a) Simple rhombohedral
5) HEXAGONAL
a=b#c&
a) Simple hexagonal
α = β = 90 & γ = 120
6) MONOCLINIC
a#b#c &
α = γ = 90 # β
a) Simple monoclinic
b) Base centered monoclinic
7) TRICLINIC
a#b#c&
α # β # γ # 90
a) Simple triclinic
3) ORTHORHOMBIC
EXAMPLE
Most of the metals & alloys crystallize in to three lattices i.e. BCC, FCC, & HCP. They are discussed
in details as follows –
i)
Fig. 2
BODY CENTERED CUBIC STRUCTURE ( BCC ):
shows schematic diagram for the
atomic arrangement of BCC structure.
The shape is cubic. There are atoms at
all eight corners of cube. Each atom is
shared by eight cubes. There is one more
atom at the center of cube. All corner
atoms
touch
crystallizing
the
center
atom. Metals
in BCC structure are αFe,
δFe, Cr, W, V, Mo, Na etc.
Number of atoms per unit cell for BCC structure is 2.
The number of atoms per unit cell is called as ‘RANK’ of unit cell. The rank of BCC is 2.
Packing density ( also called as packing efficiency ) for BCC is 0 . 68 or 68 %.
ii)
FACE CENTERED CUBIC STRUCTURE ( FCC ) :
Fig. 3 shows the schematic diagram for the
atomic arrangement of FCC structure. The
shape is cubic. There are atom at all
eight corners of cube, & there are atoms
at the centre of each face. Each corner
atom is shared by eight cubes, & each
face atom is shared by two cubes. Each
face atom touches four corner atoms.
Metals crystallizing in FCC are γ Fe, Cu,
Al, Au, Ag etc.
Number of atoms per unit cell for FCC is 4 . i.e. rank of FCC is 4.
Packing density ( or packing efficiency ) for FCC is 0 . 74 or 74 % .
iii)
HEXAGONAL CLOSE PACKED STRUCTURE ( HCP ) :
Fig. 4 shows the atomic arrangement of
hexagonal closed packed structure. There
is one atom, each at all twelve corners.
Two more atoms , one at the top face
centre & another at bottom face centre
are present. Additional three atoms are at
the
middle
layer
touching
all
other
atoms. Example of metals crystallizing
in HCP structure are Cd , Zn , Mg , Co ,
Zr, Ti , Be etc.
Number of atoms per unit cell of
HCP
is 6 i.e. rank of HCP is 6.
Packing density for HCP structure is 0.74 or 74 %
IMPERFECTIONS IN CRYSTAL :
We have studied the perfect crystal structure in previous section , but practically every crystalline
material always show at least few structural flaws. They are also called as defects or imperfections.
Imperfections are broadly divided into 4 types as follows –
a) Point Defect
c) Surface Defect
b) Line Defect
d) Volume Defect
They are described in detail as follows –
i) POINT DEFECT :
This is zero dimension defect. This defect is related to single atom. Point defect is further
divided into sub types. They are shown in fig. 5. The important types are as follows-
a) VACCANCY DEFECT : In this defect,
one atom is missing
from the regular
pattern. Under certain conditions, this defect
is also called as SCHOTTKY DEFECT. It
occurs due to normal thermal vibration of
atom in the solid. It increases exponentially
with
increasing
temperature. Solid
state
diffusion occurs due to the mechanism of
point defect motions.
b) INTERSTITIAL DEFECT : In this defect, small atoms of other element
occupy the
interstitial position. Steel, which is an alloy of Iron & Carbon, is best example of interstitial
defect. Carbon atoms occupy the interstitial spaces between the iron atoms.
c) INTERSTITIALCY DEFECT : In this defect, lattice atom is displaced from a regular site
to an interstitial site. This defect is also called as FRANKEL DEFECT.
d) SUBSTITUTIONAL DEFECT : In this defect, foreign atom of approximately same size
occupies the lattice atom position.
ii) LINE DEFECT :
This is one dimension defect. Line defects are also called as
dislocations. They are associated primarily
with
mechanical deformation. Line defects are
commonly designated by the symbol ‘⊥’. Line defect is subdivided into 2 types. They are
shown in fig. 6 –
a) EDGE DISLOCATION : In this dislocation, the defect runs along the edge of the extra
row of atoms.
b) SCREW DISLOCATION : In screw dislocation, there is spiral stacking of crystal planes
around the dislocation line.
In practice, dislocations are rarely of pure edge or pure screw type but are mixed dislocations.
iii) SURFACE DEFECT : This is two-dimension defect. It includes grain boundaries, tilt
boundaries, twin boundaries, stacking fault, surface of precipitate, external surface etc. Surface
defects occur during solidification, mechanical treatment, thermal treatment etc.
When the metal is heated, the grain size increases & number of grain decreases. This result in
to reduction in grain boundary defects.
iv) VOLUME DEFECT : This is three-dimension defect. Volume defect is also called as
bulk defect. It includes pores, cracks, foreign inclusions, & other phases. They are normally
introduced during processing & fabrication steps. Volume defects are much larger than other
defects & have pronounced effects on the properties of material.
MILLER INDICES FOR PLANES :
Crystal consists of various lattice planes (also called crystal planes ). They are either parallel or
intersecting each other. These planes are designated by three numbers, written in bracket as ( hkl )
called MILLER INDICES. Miller indices denote the orientation of crystal planes and direction in
crystal. Orientation of plane is described by coordinates to which they intersect to x , y , z-axis . i.e.
intercept of crystal plane in the orientation of that plane.
Consider a plane having intersect at 1 , 2 , 3 at x , y , z-axis respectively as shown in fig. 7.
Then orientation of the plane will be 1 , 2 , 3 . The intercepts of crystal planes are measured in terms of
lattice parameter . This has disadvantage of fraction number if plane intersect at mid point and
disadvantage of infinite number if plane is parallel to certain axis. To avoid this, Miller used reciprocal
of intercept and converted it in to whole number.
Therefore reciprocal
of intercepts 1 , 2 , 3 are 1/1 , 1/2, 1/3 . If they are converted in to
smallest whole number , it will be 6 , 3 , 2 . These whole numbers are Miller Indices for above plane and
are written as (6 3 2 ) . If the set of the planes are to be represented , then {} bracket is used ( Called as
curly bracket ). For finding out the Miller indices of any crystal , one corner of the crystal is considered
as the origin of the space coordinates .The Miller Indices of the plane DEFG are ( 0 1 0 ) .To find out the
miller indices of plane ABCO, the coordinate system has to be shifted to another corner. This is
permissible since all corners of the unit cell are equivalent. The plane ABCO then intersects the negative
Y-axis. To indicate this a minus sign is placed. Thus Miller Indices for plane ABCO are ( 01 0 ).
{ 1 0 0 }indicates all six planes of cubic unit cell represented by ( 1 0 0 ) , ( 0 1 0 ) , ( 0 0 1 ) ,
( 1 0 0 ) , ( 0 1 0 ) , ( 0 0 1 ) . The minus sign indicates the intersection at negative axis .
MILLER INDICES FOR CRYSTAL DIRECTION :
The crystal directions are the lines joining the origin and the lattice point. the miller indices for
crystal directions are again smallest whole number written in square
bracket. For e.g. [uvw].
Reciprocals are not used here but the numbers are reduced to smallest integer. The direction along x-axis
is represented by [ 1 0 0 ]; along y-axis is represented by [ 0 1 0 ]; and along z- axis is represented
by [ 0 0 1 ]. The set of crystal direction is written in < > bracket ( called as pointed bracket).
The diagonal OA is represented by [ 1 1 1 ]. The diagonal OD will be represented by [ 1 1 0 ],
while diagonal EC will be represented by [ 1¯ 1 0 ]. It is interesting to know that in cubic system the
directions and planes having same numerical Miller indices are perpendicular to each other. All
parallel lines have same Miller indices, similarly all parallel planes have same Miller indices.
QUESTIONS FOR VIVA-VOCE :
1. Define unit cell.
2. Differentiate between amorphous & crystalline materials.
3. What is the vector & angle conditions for cubic system ?
4. What is the vector & angle conditions for tetragonal system ?
5. What is the vector & angle conditions for orthorhombic system ?
6. What is the vector & angle conditions for rhombohedral system ?
7. What is the vector & angle conditions for hexagonal system ?
8. What is the vector & angle conditions for monoclinic system ?
9. What is the vector & angle conditions for triclinic system ?
10. What is mean by ‘RANK’ of unit cell ?
11. Calculate number of atoms per unit cell for BCC structure.
12. Calculate packing density for BCC structure.
13. Draw schematic diagram for BCC structure.
14. Calculate packing density of FCC structure.
15. Calculate number of atoms per unit cell for FCC structure.
16. Draw schematic diagram for FCC structure.
17. Calculate packing density of HCP structure.
18. Calculate number of atoms per unit cell for HCP structure.
19. Draw schematic diagram for HCP structure.
20. What are the types of imperfections in crystal?
21. What are the types of point defects? Explain.
22. What are the types of line defects ? Explain.
23. Explain surface defect.
24. Explain the volume defect.
25. What is the use of ‘Miller Indices’ ?
26. How to mention the Miller indices for plain & Miller indices for crystal direction ?
27. What does negative sign on Miller indices indicate ?
28. How the set of planes are represented in Miller indices ?
EXP NO. 2
AIM: STUDY OF METALLURGICAL MICROSCOPE
THEORY : Metallurgical
microscope, as the name suggests, is used to study metallic samples. It is
designed to observe the opaque specimen. Metallurgical microscope is different from biological
microscope in the fact that the biological microscope uses natural light with the help of concave
mirror. On the other hand, in metallurgical microscope separate light source is used, which focuses
the light on the specimen. It is used to observe the minute details of specimen which can not be seen by naked
eye. These microscopes uses optical lenses for magnification hence it is also called as OPTICAL
MICROSCOPE. The maximum magnification is about 2000 X , where X is the unit of magnification.
Higher magnification is not possible by optical microscope due to the limitations in the wavelength of
visible light, which limits the resolution of details in the metallographic specimen. For higher
magnification, electron microscopes like scanning electron microscope (SEM), field ion microscope (FIM),
transmission electron microscope (TEM) etc are used. Very high magnification is possible with TEM,
SEM etc, SEM has additional advantage of
allowing irregular surface to be inspected. Also, it does
not require polishing of the surface. Metallurgical microscope is very important tool in the hands of
metallurgical Engineer.
CONSTRUCTION :
Simple optical type metallurgical microscope consists of body tube which carries
eyepiece at its top, objective at its bottom, plane glass reflector in the middle portion & light attachment at the
perpendicular at middle portion. The objective resolves the image & eyepiece magnifies it. The total
magnification will be the multiplication of magnification of eyepiece & magnification of objective. Since the
metallographic specimens are opaque to light, the specimen must be illuminated by reflected light. A
monochromatic source of light is used for the illumination. A lens is fitted in front of it. An Iris diaphragm is
provided to control the beam width. A plane glass is fitted at 45 degree, which reflects the light towards the
specimen, & allows to pass the image through it. Coarse adjustment & fine adjustment knobs are provided to
adjust the distance between objective & specimen. A table is provided to place the specimen. Eyepiece &
objectives are available in variety of magnification power such as 5 X , 10 X , 45 X , 100 X etc.
TYPES : Optical microscopes are manufactured in various types. The important
optical microscope,
among them are simple
inverted stage microscope; monocular, binocular, trinocular
etc. Simple optical
microscope is shown in Fig. 1. Figure 2 shows the path of ray for optical & electron microscope.
Simple optical microscope, as the name suggests, is simple in construction, cheap in cost. There is no
provision for various attachments. When the specimen is changed, the distance between specimen &
objective has to be adjusted. This disturbs the continuity in the observation of large number of specimen.
Inverted stage microscope , as the name suggest is provided with the specimen table at the top. It
eliminates the drawback of adjusting the distance between the specimen & objective, every time when the
specimen is changed. It also accommodates various attachments. The various attachments are described
below.
i) GROUP VIEWING ATTACHMENT : It displays the structure on glass screen with enlargement .
It is very useful to explain the structure to a group or in the seminar.
ii) PHOTOGRAPHIC CAMERA : Photographic camera helps recording the structure permanently.
Monocular, binocular, trinacular microscope have one, two & three eyepieces respectively. Binocular
microscope reduces the strain on the eyes since both eyes can be used simultaneously. In trinocular
microscope, photographic attachment is provided at third eyepiece.
USES : The various uses of the metallurgical microscope are i) To find the grain size & shape.
ii) To find the grain size distribution.
iii) To find various phases.
iv) To find various inclusions.
v) To study the effect of mechanical & thermal treatment.
vi) To photograph the specimen.
LIMITATIONS :
1. Optical microscope has maximum magnification of 2000 X .
2. Specific specimen preparation is required for observation.
3. Optical microscope does not give any idea of depth in the microstructure.
QUESTIONS FOR VIVA – VOCE :
1.
What are the differences in metallurgical microscope & biological microscope ?
2.
What is mean by optical microscope ?
3.
What is the maximum magnification of optical microscope ?
4.
For higher magnification, which microscopes are used ?
5.
Name the various parts of optical microscope.
6.
What is mean by monochromatic source of light ?
7.
Why monochromatic source of light is used in optical microscope ?
8.
What is the specific advantage of inverted stage microscope ?
9.
Name various attachments to optical microscope
10.
What is the use of group viewing attachments ?
11.
What is the use of camera ?
12.
State various uses of optical microscope.
13.
Draw simple sketch of optical microscope.
14.
Draw the ray diagram for optical microscope.
15.
Draw the ray diagram for electronic microscope
16.
What is the function of eyepiece ?
17.
What is the function of objective ?
18.
What is the function of plane glass reflector ?
19.
What is the function of Iris diaphragm ?
20.
What is the function of coarse adjustment & fine adjustment ?
21.
How to calculate the total magnification of optical microscope ?
22.
What is the unit of magnification ?
23.
Why higher magnification is not possible by optical microscope ?
24.
What are the limitations of optical microscope ?
EXP NO. 3
NAME : PREPARATION OF SPECIMEN
THEORY :
To observe the effect of various metallurgical processes such as heat treatment, alloying,
mechanical working etc. the specimen is prepared to observe under the microscope. Success in microscopic
study, depends largely upon the care taken in the preparation of specimen. Specimen preparation is
specific process to be followed step by step. The ultimate objective is to produce a flat, scratch free, mirror
like surface, & then etch it for development of microstructure.
The various steps in specimen preparation are -
1. SECTIONING : This step is also called as sampling. The choice of sample is very important,
particularly for failure investigation. A small piece of metal is cut from the material to be observed. While
cutting, one must know whether it is transverse section or longitudinal section, particularly for rolled products.
In addition, while cutting, care should be taken that the temperature of metal should not increase. Otherwise,
unknowingly the specimen will be heat treated, which may change the structure. To avoid this, the
coolant may be used while cutting the metal.
2. MOUNTING : Many times the metal piece,
to be observed is not handy.
Specimen also
requires both, upper & lower surfaces, parallel to
each other & perpendicular to the rays falling on
it. This is achieved by mounting. There are two
types of mounting - i) Cold mounting ii) Hot
mounting. In cold mounting, resin powder &
liquid is used. A cold mounting die is used to
give the particular shape to mount. In hot
mounting, generally Bakelite powder is used. Hot
mounting is faster than cold mounting process.
3. ROUGH
GRINDING : The mounted specimen has sharp edges. It may torn out polishing cloth,
polishing paper and may create problems in handling. In addition, metal piece has oxide film, which should be
removed for faster polishing. These things can be achieved by grinding. For this purpose, grinding wheel, belt
grinder, or file is used. Grinding is continued until the surface is flat & free of nicks & burrs etc.
Grinding also levels the surface if any unevenness exists. Sometimes this step is performed before
mounting.
4. PAPER POLISHING : The specimen is to be mirror polished. This is done in steps. Different grades
of emery papers are used. They are available in 1/0 , 2/0 , 3/0 , 4/0 grades of successive fineness. the specimen
is polished on the papers in the sequence of increasing fineness. While shifting from one paper to another,
care should be taken that the specimen should be rotated by 90o. This is necessary to remove previous coarse
scratches.
5. CLOTH POLISHING : It is also called as final polishing , buffing, or mirror polishing. The aim of
cloth
polishing is to give mirror polish to specimen. In this process, the polishing media is poured on
cloth. This cloth is fixed on rotating disc. The various polishing media are -
a) For ferrous & copper based materials
-Alumina powder
b) For Aluminium , magnesium & their alloys
-Cerium oxide
c) For other ( Hard materials )
-Diamond paste , chromium oxide or magnesium oxide
Initially the disc is started rotating. Then large amount of water is poured on the cloth . This
will remove all dust particles . Then polishing media is poured drop by drop near the periphery . The specimen
is held lightly pressed. The specimen should be hold in such a way that the scratches are perpendicular to the
direction of polishing. This process gives mirror polish to the specimen.
6. ETCHING : Mirror polished specimen will not show any structure under microscope, since the specimen
observation is based on reflection of light, and mirror polished surface will show very bright surface since entire
light is reflected. Hence etching is essential to develop the microstructure. Etching reagents attacks different
phases preferentially . It attacks one phase first & after some time starts attacking another phase. Before it
attacks another phase , etching reagent is washed out . Hence only one phase is attacked, which appears dark
under microscope & the other phase , which is not attacked, will appear bright. The various etching reagents
are
a) For steel
-- Nital 2% ( i.e. 2 ml Nitric acid & 98 ml alcohol)
b) Aluminium & its alloys
-- Hydrofluoric acid
c) Copper & its alloys
-- Ammonia & ferric chloride solution
d) Brasses
-- chromic acid
e) Gold , Silver , Platinum
-- Aquaregia.
7. OBSERVATION : Properly etched & washed specimen is placed under the microscope. By using proper
combination of eyepiece & objective , the specimen is observed for microstructure.
PRECAUTIONS :
1. While sectioning, one must know whether it is transverse section or longitudinal section.
2. While cutting the specimen on power saw, coolant shall be added to avoid heating of specimen.
3. While mounting, the specimen shall be placed in such a way that the surface to be observed will
be exposed after mounting.
4. Grinding on surface polisher or wheel grinder shall be done slowly to avoid heating of specimen.
5. While polishing on emery paper, care shall be taken that when the specimen is shifted from one
paper to another, the specimen shall be rotated by 900.
6. Specimen shall be lightly pressed while polishing on cloth.
7. Etching reagent shall be washed away within specified time.
QUESTIONS FOR VIVA – VOCE :
1. Why specimen is observed under microscope ?
2. Mention various steps in specimen preparation.
3. What care should be taken while sectioning the specimen ?
4. Why mounting is required ?
5. What are the types of mounting ?
6. Which instruments are used for rough grinding ?
7. Why rough grinding is carried out ?
8. What are the different grades of emery papers ?
9. What care should be taken while shifting the specimen from one emery paper to another ?
10. Name various polishing media used on cloth polishing.
11. Why etching is essential ?
12. How etching reagents act ?
13. State various etching reagents.
EXP NO. 4
AIM : METALLOGRAPHY OF PLAIN CARBON STEEL
THEORY :
Metallography is the study & drawing of microstructure of specimen. Various specimens of
plain carbon steel are studied under the microscope for metallurgical studies . The specimens are selected from
dead mild steel to hyper-eutectoid steel to study the effect of increase of carbon percent on the phases present.
The description of various specimens are given below-
SPECIMEN - A1 : It is dead
mild steel (0.008 to 0.15% C)
showing
equiaxed
ferrite
grains
(white)
together
with
few
spheroidized carbide particles.
SPECIMEN - A2 : It is mild
steel (0.15 to 0.25% C) containing
about 0.2% carbon. The phases
present are ferrite (white) & pearlite
(dark). Ferrite is about 75% &
pearlite is about 25%.
SPECIMEN - A3 : It is medium
carbon steel (0.25 to 0.55% C)
containing
about
0.4%
C.
The
structure shows ferrite & pearlite, in
equal amount i.e. 50% each.
SPECIMEN - A4 : high carbon
steel (0.55 to 1.5%C) containing
about 0.6% carbon . The pearlite is
seen about 75% & Ferrite is about
25%.
SPECIMEN - A5 : It is
eutectoid steel containing about
0.8% carbon. It shows 100% pearlite
. Some of the pearlite is resolved.
SPECIMEN - A6 : It is hypereutectoid steel (carbon percent 0.8
to
2%)
in
annealed
condition,
showing white Cementite particles in
pearlite.
QUESTIONS FOR VIVA – VOCE :
1. What is the percent of carbon in dead mild steel ?
2. Which phase are seen in the microstructure of dead mild steel ?
3. What is the percent of carbon in mild steel ?
4. What are the phases present in mild steel ?
5. What are proportions of phase in mild steel containing 0.2 % carbon ?
6. What is the percent of carbon in medium carbon steel ?
7. What are proportions of phase in medium carbon steel containing 0.4 % carbon ?
8. What is the percent of carbon in high carbon steel ?
9. What are proportions of phase in high carbon steel containing 0.6 % carbon ?
10. What is the percent of carbon in eutectoid steel ?
11. Which phases are present in eutectoid steel at room temperature ?
12. What is the percent of carbon in hyper - eutectoid steel ?
13. Which phases are present in hyper - eutectoid steel at room temperature ?
EXP NO. 5
AIM : METALLOGRAPHY OF CAST IRON
THEORY :
Cast iron is an alloy of iron & carbon in which carbon content varies between 2.0% to 6.67% .
Apart from carbon , cast iron contains phosphorus, sulpher , Silicon, manganese. The description of various cast
iron specimens are given below-
SPECIMEN - B1 : The structure
shows Cementite & transformed
austenite
(i.e.
pearlite).
The
specimen is of white cast iron.
SPECIMEN
-
B2
:
The
specimen is grey cast iron. It is
showing graphite flakes (black) in a
fully pearlitic matrix. Phosphide
eutectoid is present.
SPECIMEN - B3 : It is nodular
cast iron (also called as Bull's eye
cast iron). The structure shows black
graphite nodules surrounded by a
white ring of ferrite in the pearlite
matrix.
SPECIMEN - B4 : Specimen is
of malleable cast iron. The structure
shows temper carbon.
QUESTIONS FOR VIVA – VOCE :
1. What is the percent of carbon in cast iron.
2. Apart from carbon, what are the other elements present in the cast iron ?
3. What are the phases present in white cast iron ?
4. Why white cast iron is called so ?
5. Why the name ‘Grey cast iron’ is given to a particular type of cast iron ?
6. What phases are seen under the microscope, when grey cast iron is observed ?
7. What phases are seen in the microstructure of nodular cast iron under the microscope ?
8. What phases are seen in the microstructure of malleable cast iron under the microscope ?
EXP NO. 6
AIM : METALLOGRAPHY OF NON-FERROUS METALS
THEORY : Metallic materials when considered in broad sense , may be divided into two groups i.e. ferrous
metal & non-ferrous
metals. The ferrous materials are iron based & non-ferrous materials have major
constituent elements other than iron. The important non-ferrous metals are brasses, bronzes, gun metals etc.
Some of the specimens are studied under microscope. Their description is given below-
SPECIMEN - C1 : It is 60/40
brass in annealed condition, showing
α (white) phase & β (black) phase.
SPECIMEN - C2 : It is 70/30
brass in annealed condition showing
equiaxed grains. Annealed twins are
present.
SPECIMEN
-
specimen
phosphor
is
C3
:
The
bronze
showing cored grains (white) with
interdendrites (α + δ + Cu 3 P).
SPECIMEN - C4 : It is leaded
60/40 brass in as cast condition
showing
α
interdendritic
β.
dendrites
with
Black
round
particles of lead are present.
SPECIMEN
-
C5
:
The
specimen shows Cu-Sn-Pb bearing
metal showing dendrites of tin rich
solid solution containing needles &
small particles of Cu 6 Sn 5 (white).
SPECIMEN - C6 : Annealed
(Cu- Al 10%) Aluminium bronze ,
showing equiaxed α grains (white) &
( α+ δ ) eutectoid.
SPECIMEN
-
C7
:
The
specimen is of gunmetal showing
cored
grains
with
interdendrites
(α+δ) in which δ is white.
SPECIMEN – D1 :
specimen
show
fully
The
annealed
copper with equiaxed grains and
straight grain boundaries. Annealing
twins are present .
SPECIMEN – F1:
Single
phase cored dendrites in 70 / 30
brass specimen .
QUESTIONS FOR VIVA – VOCE :
1. Define ferrous & non- – ferrous alloys.
2. Name few important nonferrous alloys.
3. What is composition of gunmetal ?
4. Why the name gunmetal is given ?
5. Define ‘Brass’
6. Define ‘Bronze’
7. What is mean by 60 / 40 brass ?
8. What is phosphor bronze ?
9. What is bearing metal ?
10. What is aluminium bronze ?
11. What is mean by ‘Dendrites’ ?
EXP NO. 7
AIM : METALLOGRAPHY OF HEAT-TREATED
SPECIMEN
THEORY :
Heat treatment is the process of heating the material to certain temperature ,
soaking ( holding for sufficient time ) at that, temperature for sufficient time & cooling at
predetermined rate. There are various types of heat treatment like annealing , normalizing ,
hardening etc. Heat treatment is carried out for various purposes , for e.g. to relieve the internal
stresses ; to harden the material ; to change the grain size & shape etc.
SPECIMEN-E1: The microstructure
shows 0.1% carbon steel in fully
annealed condition showing equiaxed
ferrite grains , with straight grain
boundaries. About 12% pearlite is
present, some of it is in the resolved
condition.
SPECIMEN - E2 : It is
normalized sample showing smaller
grain size with 20% pearlite.
SPECIMEN
-
E3
:
The
specimen is of 0.55% carbon steel in
hardened condition showing 100%
martensite.
SPECIMEN - E4 : It is
tempered specimen of 0.55% carbon
steel. After tempering at 400oC, the
specimen is showing a mixture of
ferrite & carbide particles.
SPECIMEN
specimen
showing
is
-
E5
case
tempered
:
The
carburized
high
carbon
martensite in the case & low carbon
tempered martensite with ferrite in
the core
SPECIMEN
-
E6
:
The
specimen is case carburized. The
microstructure
shows
case
with
tempered martensite and rapidly
cooled ferrite & pearlite in the core.
SPECIMEN - E7 : It is nitrided
specimen of EN 40 B, showing white
nitride layer on the surface & along
the grain boundaries. The core is
tempered martensite.
SPECIMEN D2 : 0.2 % C steel
sample in cold worked condition
showing
elongated
ferrite
&
Pearlite grains
SPECIMEN D3 : 0.05 % C steel
sheet, cold worked and heated
to about 500°C. Equiaxed ferrite
grains with
irregular
boundaries
are present .
SPECIMEN F2 : 0.35 % C steel
sample rapidly cooled from high
austenitizing temperature showing
ferrite
plated / nucleated
Widmanstaten
pattern
in
within
pearlite colonies .
SPECIMEN F3 : Banded steel
showing
Pearlite .
bands
of
ferrite
&
QUESTIONS FOR VIVA – VOCE :
1. Define heat treatment
2. What is purpose of soaking ?
3. What are the purposes of heat treatment ?
4. Define ‘Annealing’
5. Define ‘Normalizing’
6. Define ‘Hardening’
7. What type of grain structure is shown by annealed steel ?
8. What type of grain structure is shown by normalized steel ?
9. Which phase appear in fully hardened steel ?
10. Which phases appear after tempering of medium or high carbon steel ?
11. Which phases are seen in ‘Case carburized steel’ ?
12. What is seen in ‘Nitrided’ specimen, under the microscope ?
13. What is the grain shape in cold worked & hot worked specimen ?
14. What is ‘Widmanstaten Pattern’?
15. What is mean by banded steel ?
EXP NO.
NAME : HARDNESS TEST
AIM: TO MEASURE THE HARDNESS OF SPECIMEN USING 1) BRINEL 2) ROCKWELL
HARDNESS TEST.
THEORY : Hardness is defined as the property of materials by virtue of which
it resists the scratching,
abrasion, indentation, plastic deformation, penetration, cutting etc. Hardness is not a fundamental property of
material, but rather a composite one including yield strength, work hardening, tensile strength, modulus
elasticity & others. Hardness depends on grain size, yield strength, tensile strength, ductility, alloying
elements etc. Various machine-parts & structures such as gears, axles, rails etc require hardness . Hard
materials show good resistance to wear.
There are various methods for the measurement of hardness, based on different principles such
as scratch resistance, rebound , indentation resistance etc. The most commonly used test is based on
indentation resistance, in which
indenter is pressed in to the surface of the material by a slowly
applied known load. The extent of resulting penetration is the measure of hardness. A large indentation
indicates soft material & small indentation indicates a hard material. The various hardness tests using the
principle of indentation are Brinnel, Rockwell , Vickers etc. With the help of charts, hardness numbe can be
converted from one type to another. These are semi-destructive type testing methods.
1) BRINNEL HARDNESS TEST : Brinell hardness test is more accurate than other hardness test due to
more area of contact between indenter & specimen. In this test, a hardened steel ball of specified diameter
( e.g. 2.5 mm, 5 mm, 10 mm etc ) is used. Bigger the diameter, higher is the accuracy. Selection of ball
diameter depends on type of materials to be tested. Depending on the ball diameter, the corresponding
load is fixed. Softer the material, lesser is the load & smaller is the ball diameter. Harder
the
material, more is the load & larger is the ball diameter. For the general specimen, a ball of 2.5 mm diameter
with 187.5 Kg load is used. The permissible error in the measurement of indentation is as follows – a) ± 0.04
mm for hardness below 225 BHN b) ± 0.02 mm for hardness above 225 BHN.
PROCEDURE : The specimen is placed on anvil. A steel ball of selected size is fixed in the ball holder.
Specimen is brought in contact with ball by rotating screw. Zero load setting is carried out by bringing the
small pointer to red spot in the dial indicator for dial guage indicator type machine. In case of digitial
display, initial load is applied till all zero appears on display, the LED of SET glows.. Then appropriate load is
applied for specified time, which presses the ball against the specimen, & creates indentation. The diameter of
indentation is measured at two places, right angle to each other, using micrometer microscope . The average
of two reading is taken. By using following formula Brinnel hardness number (BHN) is calculated -
BHN =
Where W =
2W
------------------------------------( Π D ) ( D - √ D2 - d2 )
Load on indenter in kg.
D=
Diameter of steel ball in mm.
d=
Average diameter of indentation in mm.
Brinnel Hardness Number is load per unit surface area of the indentation in kg / mm2 , but the unit is rarely
used. Brinnel hardness number can also be found out from chart available for ready reference. A well
structured BHN is written as 75HB 10/500/30 indicates a Brinnel hardness number of 75 obtained using a 10
mm diameter hardened steel ball with a 500 Kg load applied for a period of 30 seconds. Figure 1 shows the
hardness testing machine, which can be used for Brinnel, Rockwell, Vicker hardness test etc.
FIG 1.
HARDNESS TESTING MACHINE
2) ROCKWELL TEST : Rockwell hardness test is the most used & versatile of hardness test. This test is
used for various
materials. Various Rockwell
scales
i.e A,B,C,D,E,F,G,H,K,L,M,P,R,S,V have
been
designed to suit the various requirements. Among these A,B,C, are most common. Their uses are as follows –
Scale A
-
Cemented carbide, thin sheet, shallow case hardened steel, case carburized surfaces.
Scale B - Aluminium alloys, Copper alloys, malleable iron, Unhardened steel etc. in rolled, drawn, extruded or
cast metal
Scale C – Hard cast iron, Pearlitic, Malleable iron, steel, deep case hardened steel, titanium, material harder
than 100 HRB
Rockwell hardness testing is faster, since machine itself gives direct reading . In addition, this test does not
require special skills. With different indenters & different scale, virtually all metals from the hardest to
the softest can be tested by this method. For the soft materials, steel balls of specified sizes are used.
For hard material, conical diamond indenter with tip cone of 1200 & 0.2 mm radius, called as Brale, is used.
Hardness number is determined by the difference in the depth of penetration graduated in special
units, resulting from the application of an initial minor load of 10 Kg. followed by a larger major load,
& it is indicated directly by dial gauge pointer. Hardness number has no units.
PROCEDURE ( FOR DIAL GUAGE INDICATOR TYPE MACHINE ) :
1) Keep the lever at position A.
2) Select suitable indenter according to type of material & corresponding scale.
3)Place the job on testing table
4) Turn the hand wheel to raise the job, making contact with penetrator and continue turning until the
long hand of the dial gauge has made two & half turn. Then it stops at ‘0’. Continue turning
further, until the small hand reaches red spot at ‘3’. This is automatic zero setting & manual
adjustment is not necessary.
5)Turn the lever from position ‘A’ to position ‘B’ so that the total load act.
6)When the long pointer of dial gauge reaches a steady position, take the lever back to position ‘A’
slowly.
7)Read the figure against long pointer. Outer black scale is used for Rockwell A & C. The inner red
scale should be used for Rockwell B.
8) Turn back the hand wheel & remove the job.
PROCEDURE ( FOR DIGITAL DISPLAY INDICATOR TYPE MACHINE ) :
1) Keep the lever at position A of machine shown in fig. 1
2) Select suitable indenter according to scale.
3) Place the job on testing table.
4) Set the scale on the required scale of HRA, HRB or HRC
5) Set the mode on STD
6) Turn the handwheel to raise the job, making contact with penetrator & continue turning until the four zero
appear on the screen & an indicator of SET glows with beep sound. This is automatic zero setting.
7) Turn the lever from position A to position B so that the total load act.
8) Wait until the display stabilizes & thereafter bring the lever back to position A.
9) Direct reading on display will give Rockwell hardness value.
i) OBSERVATION TABLE FOR BRINNEL HARDNESS TEST :
SN
1
2
3
A) Diameter of steel ball / Indenter ( in mm )
=
_________
B) Material of the Specimen
=
_________
C) Load on Indenter ( in Kg. )
=
_________
HORIZONTAL
VERTICAL
INDENTATION INDENTATION
mm
mm
AVERAGE
INDENTATION
mm
BRINELL
HARDNESS
NUMBER
AVERAGE
HARDNESS NUMBER
ii) OBSERVATION TABLE FOR ROCKWELL HARDNESS TEST :
a) Load on indenture ( in Kg ) = _________
c) Type of indenture
b) Scale
d) Material of the Specimen = _____________
= _________
SN
ROCKWELL HARDNESS
= _____________
AVERAGE HARDNESS
1
2
3
RESULT
: 1) Brinnel hardness of given specimen is _____________ BHN.
2) Rockwell hardness of given specimen is ____________ HRC.
PRECAUTIONS
: 1) Always take four readings. Do not lift the job after first reading. First reading is
always erratic due to air cushion between job & table. Hence, neglect it & take the average of further three
readings.
2) Test machine should be protected from shock & vibrations.
3) The thickness of the test piece shall be at-least 8 times the depth of
permanent indentation.
Deformation shall not be visible at the back of test piece.
4) The distance between the centers of the two adjacent indenters shall be at-least 4 times the diameter
of the indentation. The distance from the centre of any indentation to the edge of the test piece
shall be at-least 2.5 times the diameter of the indentation.
5) Test piece shall be placed on rigid support.
6) The contact surfaces shall be clean & free from foreign matter such as scale, oil & dust etc.
QUESTIONS FOR VIVA – VOCE :
1.
Define hardness.
2.
What are the factors, on which hardness depends ?
3.
Why hardness is desired in some machine components ?
4.
What are the various principles used for the measurement of hardness ?
5.
What is indicated by large indentation & small indentation in hardness test using principle of
indentation ?
6.
Name the various hardness test using principle of indentation.
7.
Which indenture is used in Brinnel hardness test ?
8.
State the formula to calculate the BHN.
9.
Which indenter is used to test hard materials by Rockwell hardness test ?
10. Which indenter is used to test soft materials by Rockwell hardness test ?
11.
What precautions shall be taken while performing hardness test ?
EXP NO. 09
NAME : HARDENABILITY TEST
AIM : TO DETERMINE HARDENABILITY OF GIVEN SPECIMEN USING
JOMINY END - QUENCH HARDENABILITY TEST.
THEORY :
Hardenability is the ease with which a steel piece can be hardened. It is also the depth of hardening
produced under given condition of cooling. Hardenability depends on content of alloying elements & grain size
of the material. Coarse-grained material has better hardenability than fine-grained material. This is due to the
fact that grain boundary reduces the cooling rate. Any factor that reduces the cooling rate will decrease the
hardenability. Hardenability is different than hardness. Hardenability is an ability to harden while hardness is a
measure of the resistance of material to plastic deformation. There are
various methods to determine the
hardenability. For e.g. Grossman method, Jominy end quench method etc.
JOMINY END QUENCH TEST :
This is a standardized test. Hence, all the dimensions are fixed. In this test, the specimen is prepared
of cylindrical shape of 25.4 mm diameter & 102 mm in length. An additional collar of 28 mm diameter
& 5 mm thick is provided at one end, which supports the specimen in fixture. A slight taper is provided at
the bottom for proper impingement of water. A suitable fixture is designed to hold the specimen, nozzle for
water jet etc. The fixture is placed in tray to collect the water & dispose it off. The water jet pipe has internal
diameter 12.7 mm. The distance between the specimen & the end of jet pipe is kept 12.7 mm. The pressure of
water jet is adjusted in such a way that free jet will achieve a height of 64 mm. The temperature of water is
adjusted between 21 & 270 C. Initially, the specimen is heated to (AC1+50) or (AC3+50) in the furnace. It is
soaked for sufficient time. The specimen is then removed from the furnace & placed on a fixture within
minimum
time. Immediately the water is impinged on specimen by the nozzle provided below it. The
impingement of water on specimen is carried out until specimen attains room temperature.
FIG 1. STANDARD SET-UP FOR JOMINY END-QUENCH TEST
The specimen is quenched from one end. Hence, at different distances from this end, the cooling rate
would be different. The rate of cooling at jet end where the specimen is water quenched, is about 3000 C
per second while that other end where the specimen is air cooled, is 30 C per second. The varying cooling
rate produces a wide range of hardness along the length of specimen.
Once the specimen attains the room temperature it is removed from fixture & two flat parallel surfaces
are ground opposite to each other, along the entire length of specimen. The specimen is tasted for hardness
using Rockwell - C scale at an interval of 1.6 mm . The interval may be reduced to 0.8 mm near quenched end
to make the measurement precise.
A curve is plotted between hardness value on Y- axis & distance from quenched end on X-axis, using
the data from observation table. It can be observed from the graph that the hardness changes more
rapidly in the region of 50 % martensite i.e. at 54 Rc. The distance at which we get 50 % martensite ( i.e. 54 Rc
) is known as critical distance or Jominy distance. The more is the distance, greater is the hardenability . The
hardenability is reported in terms of points, where 1 point = 1.6 mm from quenched end to 50 % martensite
cross section. In other words, Jominy distance is converted in to points ( 1 point = 1.6 mm ) & is
expressed as hardenability.
FIG.2 GRAPH SHOWING HARDNESS VS DISTANCE FROM QUENCHING END
OBSERVATION TABLE
SN
DISTANCE
HARDNESS
01
02
03
04
05
06
07
RESULT : 1) From
the curve, the Jominy distance
2) The hardenability of the specimen
PRECAUTIONS : 1) Specimen
= ____________ mm
= _____________ points
should not be overheated in the furnace
2) After soaking, the test specimen shall be transferred immediately to the furnace without any delay.
3) Hardness shall be measured at correct distance.
QUESTIONS FOR VIVA – VOCE :
1. Define hardenability
2. Hardenability depends on which factors ?
3. Name various hardenability testing methods ?
4. Draw the diagram of specimen used in ‘Jominy End Quench Test’ with all dimensions.
5. What should be the pressure of water jet ?
6. What should be the temperature of the water ?
7. What is the cooling rate of specimen at water cooled end and air cooled end ?
8. At what distances, hardness measurement is carried out ?
9. Which hardness testing method is adopted for hardness measurement?
10. Define ‘Jominy distance’ or ‘critical distance’
11. How the hardenability is expressed in Jominy test?
12. What precautions shall be taken during ‘Jominy Hardenability test’ ?
EXP NO.
NAME : TENSION TEST
AIM : TO FIND OUT TENSILE STRENGTH OF GIVEN SPECIMEN
THEORY :
Tensile test is very important for study of the behavior of engineering materials. This test helps to find
out % elongation of specimen; ultimate tensile stress; breaking stress; yield stress; Young's modulus & %
reduction of area. For designing the machine components, which will be subjected to tensile load, one must
know the above properties. The test specimen is prepared usually of right circular cylindrical shape. In general,
the diameter (d) should not be less than 4 mm; the gauge length ( Lo ) should be atleast five times its diameter.
The test specimen is always loaded axially. The specimen will elongate in axial direction & will reduce in
lateral direction . Up to certain value of load, the stress will be proportional to strain . The stress strain curve up
to this load will be a straight line. This is called proportional limit . At slightly higher load, elongation increases
at a faster rate without any appreciable increase in load. The stress corresponding to this load is called as
Yield stress (6y). On further loading the material starts strain hardening . Beyond certain values of load , the
neck formation starts & load decreases . The stress corresponding to peak load is called ultimate tensile stress
(6u) . Finally at one stage, the specimen ruptures . The corresponding stress is called as rupture stress. A sample
stress strain graph for ductile material is shown below –
Fig. 1 Stress Strain Graph For Ductile Material
The various points to be noted about stress – strain curve are as follows –
a) If the material undergo large plastic deformation before fracture then the material is ductile. Generally
the material is said to be ductile when the elongation is greater than 5%.
b) If the material exhibit little or no plastic deformation at failure then the material is brittle.
c) A point up to which the stress & strain is linearly related, is called proportion limit.
d) The largest stress in the stress strain curve is called ultimate stress.
e) The stress at the point of rupture is called fracture or rupture stress.
f) The region of the stress strain curve in which the material returns to the un-deformed stress when
applied force is removed is called elastic region.
g) The region in which material deforms permanently is called plastic region.
h) The point demarcating the elastic from the plastic region is called the yield point. The stress at yield
point is called as yield stress.
i) The permanent strain when the stresses are zero is called as plastic strain.
j) The offset yield point is a stress that would produce a plastic strain corresponding to the specified
offset strain.
k) The raising of the yield point with increasing strain is called strain hardening.
l) The sudden increase in the area of cross section after ultimate stress is called necking.
PROCEDURE : 1) Prepare the test specimen as per guideline.
the specimen in grips & select suitable scale. 4) Set the scale.
2) Measure the gauge length. 3) Insert
5) Start the machine & record the various
variables like load, increase in length etc.
Fig. 2 Tensile Test Specimen
OBSERVATION :
1) Original diameter of test specimen
do
= _____________ mm
2) Diameter of specimen after fracture
df
= _____________ mm
3) Original gauge length
Lo
= _____________ mm
4) Final gauge length
Lf
= _____________ mm
5) Original cross section
Ao
= _____________ mm2
6) Final cross section
Af
= _____________ mm2
EXPERIMENTAL DATA :
SN.
Load
(Kg)
Scale
Reading
Increase
in length(dl)
Stress
Stain
1.
2.
3.
4.
5.
6.
A graph is plotted using this data, called as engineering stress strain curve, is attached herewith.
Failure of various type of materials is shown here.
Fig. 3 Failure of Material
CALCULATIONS & RESULT :
Wp
= __________ kg/mm2
=__________ N/mm2 ( MPa )
= __________ kg/mm2
=__________ N/mm2
3) Ultimate tensile stress, 6u =----------Ao
Wf
= __________ kg/mm2
=__________ N/mm2
4) Rupture stress = Fracture Stress = ----------Ao
6
= __________ kg/mm2
=__________ N/mm2
5) Modulus of elasticity = --------ε
Lf - Lo
6) % elongation = -------------- X 100
L0
Ao - Af
7) % Reduction in area =------------ X 100
Ao
= __________ kg/mm2
=__________ N/mm2
1) Proportional limit
6p = -----------Ao
Wy
2) Yield stress,
6y = ---------Ao
Wu
= ___________
= ___________
Where –
Wp = Load at proportional limit
Ao = Original Area
Wy = Load at Yield Point
Wu = Highest Load
Wf = Load at fracture
ε
= Strain
Lo = Original Length
6 = Stress
Lf = Final Length
Ao = Original Area
Af = Final Area
PRECAUTIONS :
1) The gauge length portions should be free from any stress raiser.
2) The loading must be perfectly axial .
3) Loading should be gradual.
4) Measuring equipments should be accurate.
QUESTIONS FOR VIVA – VOCE :
1. Define proportional limit.
2. Define yield stress.
3. Define ultimate tensile stress.
4. Define rupture stress.
5. Draw ideal stress strain curve for ductile material.
6. Draw general stress – strain curve for medium carbon steel.
7. Draw general stress – strain curve for brittle material.
8. What information can be obtained from tensile test.
9. What are the dimensions & proportions of specimen for tensile test.
10. Mention the procedure of tensile test
11. What precautions shall be taken while performing tensile test.
EXP. No.
NAME : IMPACT TEST
AIM : TO DETERMINE THE IMPACT STRENGTH OF SPECIMEN BY
a) CHARPY b) IZOD TEST
THEORY:
Toughness of material can be found out by its impact strength. Toughness is the ability of the
material to absorb energy during its deformation when it is subjected to impact loading. This property is
essential for the material of machine components which are subjected to impact loading, shocks and
vibrations. It is well known that the brittle material takes little energy to start crack & little more to
propagate while ductile material require a high energy load to initiate & propagate the crack. Impact
loads is commonly occurring during service condition. Impact test is carried out to determine the energy
absorbed in fracturing test piece at high velocity. Among the various impact test, the notched bar tests
are most common. There are two types of notched bar test a) Charpy test b) Izod test.
Fig. 1 Impact Test Machine
The impact-testing machine, as shown in fig. 1 is rigid & strong structure of two columns on heavy
base. It has heavy swinging pendulum on a frictionless pin, at top. Machine has support platform at
bottom for specimen. A circular disc scale is mounted concentric to pin. This scale reads the position of
pendulum, which is calibrated in terms of potential energy of pendulum.
A) CHARPY TEST : It is standardized test. In charpy test, a rectangular bar of 10 mm. × 10mm
size is taken, of the material to be tested. It is cut to a length of 55mm. A ‘ V ’ notch of 450 angle & 2mm
depth is cut at the center as shown in fig.____. Alternately, a U notch or keyhole notch, 5 mm deep with
1 mm radius of curve at the base of notch may also provided.
Fig. 1. Specimen for charpy test.
The specimen is placed in the impact-testing machine in a vice such that the specimen is simple beam
supported at both the ends as show in fig.___.
Fig. 2 Position of specimen in Charpy Test
PROCEDURE FOR CHARPY TEST1) Raise the pendulum & hang it to appropriate place so that the energy stored in pendulum should be
300 N- M
2) Place the specimen on anvil such that the notch is opposite to the direction of blow.
3) Release the pendulum so that specimen is broken due to pendulum’s momentum.
4) Note the reading on scale.
5) Repeat the procedure for 3 specimens.
OBSERVATION TABLE FOR CHARPY TESTSr. No.
ENERGY ABSORBED BY PENDULUM,
N – M OR J
AVERAGE ENERGY ABSORBED BY
PENDULUM, N – M OR J
1
2
3
B) IZOD TEST
It is also a standardized test. In Izod test, a rectangular bar of the size 10 mm × 10mm × 75mm.
is taken of the material to be tested. A ‘ V ’ notch of 450 angle & 2 mm depth is cut at the distance of 28
mm from one end as shown in fig. 4.
Fig. 4 Specimen For Izod Test
The specimen is hold in a voice such that the specimen is cantilever as shown in fig. 5 The blow of
hammer is at 22 mm form notch center. The direction of blow is shown in fig. 5.
Fig. 5 Position of specimen in Izod Test
PROCEDURE FOR IZOD TEST :
1) Raise the pendulum & hang it to appropriate place.
2) Place the specimen in the vice such that the grove faces the hammer.
3)Release the pendulum so that specimen breaks due to pendulums momentum.
4) Note the reading on scale.
Repeat the procedure for 3 specimens.
OBSERVATION TABLE FOR IZOD TEST.
Sr. No.
ENERGY ABSORBED BY
PENDULUM, N-M OR J
AVERAGE
1
2
3
RESULT :
a ) Charpy test - The average energy absorbed by specimen
= ___________ N- m
b ) Izod test
= ___________ N – m.
- The average energy absorbed by specimen
PRECAUTIONS : 1) Specimen should be prepared carefully, particularly the notch.
2) In izod test, hold the specimen firmly.
3) During the test the position of notch should be as specified.
4) Do not allow anybody to stand within the range of swing of pendulum.
5) The test pieces shall be machined allover.
QUESTIONS :
1. Why impact strength is essential in material ?
2. Which mechanical property of material indicates, its impact strength ?
3. Name two tests, carried out for finding out impact strength of material.
4. Draw the diagram of specimen used for Charpy test. Show all dimensions & notch angle.
5. Draw a diagram showing the position of specimen in Charpy test.
6. Draw a diagram of specimen used for Izod test. Show all dimensions and notch angle.
7. Draw a diagram showing the position of specimen in Izod test.
8. What should be the amount of energy stored in pendulum ?
9. Why the test is performed for three times ?
10. What precautions shall be taken while performing impact test ?
EXP. No. 11
CRUSHING TEST
AIM - TO FIND OUT THE CRUSHING STRENGTH OF GIVEN SPECIMEN.
THEORY-
It is destructive type of material testing in which representative specimen are tested for
crushing failure.
Compression load is common type of load experienced by many components in use. Under
compressive load, the ductile materials ( for e.g. mild steel, aluminium etc.) fail in compression while the
brittle materials ( for e.g. grey cast iron, concrete etc. ) fail in crushing. It is necessary to know the compressive
strength / crushing strength of material for proper design. Fig. 1 shows crushing strength testing machine. This
test can also be performed on universal testing machine.
FIG. 1. COMPRESSION TESTING MACHINE.
PROCEDURE. 1) Measure the cross sectional area of specimen.
2) Clean the bearing surface of testing machine.
3) Insert the specimen in between the jaws of testing m/c.
4) Start applying the load gradually.
5) Note down the load at which the specimen fails.
6) Release the load & remove the specimen.
7) Repeat the procedure for 3 specimens
OBSERVATION TABLE.
Sr
No
Specimen Length
mm.
Breadth Area
mm.
mm2.
Maximum
Load
Load in
N
Kg.
Compressive
Average
strength
Compressive
N / mm2
Strength
N / mm2
01.
02.
03.
RESULT- The compressive strength of given material is_______________ N / mm2
PRECAUTION- 1) Load should be applied gradually.
2) Specimen should be defect free.
QUESTIONS FOR VIVA – VOCE :
1. What is crushing strength ?
2. Differentiate between crushing strength & compressive strength.
3. What kind of the materials fail in crushing ?
4. What kind of the materials fail in compression ?
5. Why it is necessary to know the crushing / compressive strength of materials ?
6. What various machines are used to perform the crushing / compressive test ?
7. What precautions shall be taken while performing crushing / compressive test ?
8. Mention the type of crushing / compressive test ?
EXP NO. 13
AIM : STUDY OF EFFECTS OF ALLOYING ELEMENTS ON
PROPERTIES OF PLAIN CARBON STEEL
THEORY :
The Steel may be classified as plain carbon steel & alloy steel. Alloy steel is that steel which contains
elements ( apart from carbon ) like Ni, Mn, Cr, W, Mo, V, P, Si, Ti, Zr, Nb, Al etc. to enhance one or more
properties. Alloy steels are superior to plain carbon steel in almost all respect. Following are the effects of
alloying elements -
a) SOLID SOLUTION STRENGTHENING / HARDENING : Most of the alloying elements are
soluble in ferrite to some extent & form solid solution. Solid solutions are harder & stronger & hence increase
the strength & hardness of steel. Elements like P, Si , Mn, & Ni are more effective for solid solution
strengthening
b) FORMATIONS OF CARBIDES : Some of the alloying elements combine with carbon & form
carbide. These carbides are hard & hence increase wear & abrasion resistance. Following elements are carbide
former Ti, Zr, V, Nb, W, Mo etc.
c) FORMATION OF INTERMEDIATE COMPOUND : Some elements form intermediate
compounds with iron for e.g. FeCr, Fe3 W2 etc. These phases are brittle & hence undesirable.
d) FORMATION OF INCLUSIONS : Some of the elements combine with oxygen & form oxides. It is
sometime desirable & sometime non-desirable. The elements, which form oxides, are Si, Al, Mn, Cr, V, Ti etc.
e) SHIFTING OF CRITICAL TEMPERATURE & EUTECTOID TEMPERATURE : The
alloying elements lower or raise the critical temperature. The elements, which are austenite stabilizer, (Ni, Mn
etc), lowers the eutectoid temperature (i.e. A1 ). While the elements which are ferrite stabilizer (Ti , Mo)
increases eutectoid temperature(i.e . A1 ).
f) LOWERING OF CRITICAL COOLING RATE : Most of the alloying elements such as Mn, Mo
Cr, Ni etc (except Co) Shifts the T.T.T. diagram to the right side thus decreasing the critical cooling rate. It
increases the hardenability of steel.
g) CHANGES IN VOLUME DURING TRANSFORMATION :White transforming from
Austenite to martensite, there is volume change. This change is different for different alloying elements. These
elements should be selected so that this volume change is minimum. Otherwise quench crack may occur.
h) INCREASED CORROSION & OXIDATION RESISTANCE : Some alloying Elements (e.g.
Cr , Ni ) increases corrosion & oxidation resistance.
Alloying elements are classified into two different groups-
GROUP - I - a) CARBIDE FORMING ELEMENTS e.g. Ti , Zr, V, Nb , W Mo , Cr, Mn
b) NEUTRAL ELEMENTS e.g. Co
c) GRAPHITIZING ELEMENTS e.g. Si , Ni , Cu & Al
GROUP -II - a) AUSTENITE STABILIZER - Some alloying elements ( e.g. Ni , Mn , Cu, C, and N )
make the austenite stable from room temperature to melting temperature. This steel is called
as austenitic steel.
b) FERRITE STABILIZER - Some elements (e.g.. Cr , W , Mo, V, Si , Al , B , Zr , Nb, P ,Ti)
raises A3 temperature & therefore ferrite may exists from room temperature to melting point.
This steel is called ferritic steel.
EFFECTS OF PARTICULAR ALLOYING ELEMENTS :
1) SULPHUR : Sulphur reacts with iron & ferrous iron sulphide (FeS). It is hard & brittle . It has low
melting point & freezes last during solidification. Due to this , it appears along grain boundaries. During forging
. This process is called hot short . This problem is eliminated by restricting the sulphur below 0.05 % & adding
the
Mn more than 5 times the amount of Sulphur . The presence of sulphur & Manganese increases
machinability by helping to break the chips & reducing tool wear.
2) PHOSPHORUS : It dissolves in ferrite & increases its strength & hardness. Addition of large quantity
reduces the ductility. Therefore, cracks develop during cold working operations making the steel cold short.
Generally, it is kept below 0.05%.
3) SILICON : It dissolves in ferrite & increases the strength , hardness & toughens without loss of ductility.
It is strong deoxidizer. It is added in the molten steel in the range of 0.1 to 0.3 %. Silicon is intentionally added
in spring steels, chisels, punches, & automobile valves to increase the toughness. In tool steel, it is kept below
0.2%, since it is strong graphitizer & decompose the carbides into graphite.
4) MANGANESE : It dissolves in ferrite & increases yield strength, tensile strength , toughness, &
hardness. It is least expensive & hence added in all structural steel for strengthening. It reduces harmful effects
of sulphur & increases hardenability. Mn is kept below 0.5 % to avoid temper embrittlement. Mn content
between 2 to 10 % make the steel brittle & hence useless . But higher percentage (i.e. 12 to 14 %) when added
in a steel with 1 to 1.2% Carbon, produces extremely tough , wear resistant & non magnetic steel called as
Hadfield manganese steel.
5) NICKEL : It dissolves in ferrite & increases hardness , tensile strength , and toughness without loosing
ductility . It is austenite stabilizer. It also increases corrosion & oxidation resistance , impact resistance etc. Ni
reduces coefficient of thermal expansion . It increases hardenability of steel.
6) CHROMIUM : It increases hardenability of steel . It forms carbide & increases hardness & wear
resistance. It causes secondary hardening of steel giving high red hardness. It increases corrosion & oxidation
resistance. The disadvantage of chromium is that it makes the steel temper embrittle in the range of 500 to
5500C.
7) TUNGSTEN : It increases hardenability. It forms carbide & increases wear & abrasion resistance. It
imparts red hardness i.e.. secondary hardening tendency . Hence used for making high-speed steel. It refines the
grain size & reduces the tendency of decarburization.
8) MOLYBDENUM : It works almost similar to tungsten, except grain coarsening & decarburization is
less. It reduces temper embrittlement
9) VANADIUM : It shows same effects as that of Tungsten ( and that of molybdenum also ) with some
distinct properties- It is strong carbide former. It increases wear resistance, creep resistance & imparts red
hardness to steel. It resists the grain coarsening . When 1 % of vanadium is added, it produces high-speed steel
of the hardness 65-66 Rc. And when 5 % V is added, it produces super high-speed steel of hardness 70 – 72
Rc. It improves fatigue & creep resistance. Hence used for leaf & coil springs. It is strong deoxidizer.
10) TITANIUM : It is strong carbide former. It resists grain coarsening. It is added in stainless steel to prevent
precipitation of chromium carbide.
11) COBALT : It is the only element, which reduces hardenability of steel . It increases red hardness . It
improves magnetic properties & hence added in permanent magnet . It increases creep resistance.
12) ALUMINIUM : It is powerful deoxidizer. It is also grain refiner & inhibitor.
13) BORON : Small addition i.e. 0.001 - 0.003 % increases hardenability of medium carbon steel . It
improves machinability of steel. Boron diffuses into the surface & produces high surface hardness, wear
resistance & corrosion resistance.
14) CARBON : It increases hardness of plain carbon steel when added up to 0.8 %. It decreases the
melting point of steel when added up to 4 .3 % & beyond that again increases the melting temperature.
It increases the strength , hardness etc. It improves machinability. It decreases ductility. It affects the
tensile strength , toughness etc.
15) COPPER : It increases resistance to atmospheric corrosion. It acts as strengthening agent. The
addition of copper is usually in the range of 0.1 to 0.6 %
16) LEAD : It improves machinability when added less than 0.35%
QUESTIONS :
1. What is the classification of steel ?
2. What is mean by alloy steel ?
3. Why alloying elements are added in to steel ?
4. What are the effects of alloying elements on properties of steel ?
5. Which elements causes solid solution strengthening / hardening ?
6. Which elements form carbide ?
7. Which elements form intermediate compound ?
8. Which elements form inclusion in steel ?
9. Which elements act as austenite stabilizer ?
10. Which elements acts as ferrite stabilizer ?
11. Which elements lower the critical cooling rate ?
12. What are the different groups of alloying elements ?
13. What are the effects of sulphur on the properties of plain carbon steel ?
14. What are the effects of phosphorus on the properties of plain carbon steel ?
15. What are the effects of silicon on the properties of plain carbon steel ?
16. What are the effects of manganese on the properties of plain carbon steel ?
17. What are the effects of nickel on the properties of plain carbon steel ?
18. What are the effects of chromium on the properties of plain carbon steel ?
19. What are the effects of tungsten on the properties of plain carbon steel ?
20. What are the effects of molybdenum on the properties of plain carbon steel ?
21. What are the effects of vanadium on the properties of plain carbon steel ?
22. What are the effects of titanium on the properties of plain carbon steel ?
23. What are the effects of cobalt on the properties of plain carbon steel ?
24. What are the effects of aluminium on the properties of plain carbon steel ?
25. What are the effects of boron on the properties of plain carbon steel ?
26. What are the effects of carbon on the properties of plain carbon steel ?
27. What are the effects of copper on the properties of plain carbon steel ?
28. What are the effects of lead on the properties of plain carbon steel ?
EXP 14
MICRO – HARDNESS TESTING
INTRODUCTION :
Micro-hardness is the hardness of very small area with very small indentation. Micro – hardness
testing is carried out to measure the hardness of various phases & micro-constituents present in the metal
matrix, thin wires, sheets, diffusion coatings, carburized & nitrited components, case hardened material,
ceramic materials etc. These hardness testing can not be done by regular hardness testing machine.
INSTRUMENT :
It is a specially designed opto-mechanical instrument consisting of metallurgical microscope with
adjustable specimen table & arrangement for indentation is used for measuring the microhardness. The
instrument is precise & delicate to handle. The measurement can also be done with the help of software
which gives direct report.
The instrument of microhardness testing is provided by
M/S. Vaiseshikha Electron Devices,
Amballa Cantt. It has the range of measurement from 10 to 150 HV. The accuracy of the system is ± 10
Vickers for hardness less than 100 Vickers & ± 20 Vickers for hardness for 100 to 1500 Vickers.
PRINCIPLE :
The principle of operation is based on pressing diamond indenter of square base pyramid with an
angle of 1360, in to the specimen under the test with a certain load & consequently measuring the linear
values of diagonal of the impression obtained in division of the micrometer drum.
The hardness number is given by the formula
1.854 X Load in Kg
HV = ----------------------------------------------------------------( Least Count X Div. of Filar Micrometer Drum )2
1.854 X Load in Kg.
= ---------------------------------------------------------------( 0.000138 X Division of Filar Micrometer Drum )2
PROCEDURE :
1. Prepare the surface of the specimen for microhardness testing. Mirror polishing of the specimen is
required. Also both sides of the specimen should be parallel to each other.
2. Put the specimen on the specimen table below the objective & focus the specimen with the help of
coarse & fine adjustment.
3. Rotate the table by 1800 to bring the specimen below diamond indenter.
4. Put appropriate load & lower the indenter to load the specimen.
5. Wait for 5 to 15 seconds & raise the indenter.
6. Rotate the table again by 1800 to bring the specimen back to microscope.
7. An indentation will appear on the specimen.
8. With the help of filar micrometer, measure both the diameter of indenter & take the average.
9. With the help of formula, calculate Vicker,s hardness
10. Alternately, the measurement of diameter of the indenter can be done with the help of software to
get the micro-hardness & then report.
OBSERVATION :
DIAMETER -1
DIAMETER – 2
AVERAGE DIAMETER
HV
RESULT : The micro-hardness of given specimen was found ______ HV
PRECAUTIONS :
1. Do not turn the specimen table when the indenter is loaded. Otherwise the diamond pyramid will get
damaged & instrument will get misaligned.
2. Surface preparation before hardness testing is very essential.
3. Protect the instrument from jerks, vibrations etc. Otherwise the instrument will loose alignment &
the impression of the indenter will not come in the centre of the field of area of MHT.
4. Thickness of the sample should be more than 1.5 times print diagonal. Distance between two
adjacent print centre should be more than two print diagonals.