Material Science Lab Report 1st year 2nd semester | MT 101
AbstractThis report includes details of the experiments done on
three particular samples A and B, to discuss their views on the
micro-structural, crystal structures, impact toughness and
hardness, and verification, and finally the name of a sample of the
properties of the concept.The given sample A is a hot-rolled
element whereas B is a cold-drawn element.First, the model set A
and B were examined under the microscope after a few steps of the
procedure and the basic structures and the availability of the
different phases were clearly discussed. This was able to give
specific properties of the specimen, which are both of them are
mild steels with less carbon percentage.Then sample A and B were
subjected to Rockwell hardness test and the obtained values were
prepared a graph. From this sample variation of hot rolling, cold
drawing the specimen and temperate zones were clearly discussed.
Furthermore, this particular experiment gave experience to operate
the Rockwell hardness tester in all situations.Finally the samples
were tested for resistance to different temperature impact and
range is clearly understood. It also obtained equipment use and
understanding of the fragility and ductility.After the end of the
three experiments, we obtained the final results, discussed in
detail and through the website, www.matweb.com the final name of
the sample were found out AISI standard.The introduction of the
three experiments, as well as the stage, the methodology used in
each experiment, discussion of results, observations, calculations
and conclusions were included in this report.In one line, this
report includes the skills and commonalities throughout the module
engineering materials.
IntroductionThe main objective of this lab sessions were to give
a basic idea on the type metal available and understand the
mechanical properties. During this lab sessions we got a basic idea
on some of the test procedures used in the industry to determine
the properties of materials. Sample A Sample B
Sample A: Hot rolled (having wavy surface is an indication for
such work on a metal) Tensile strength is around 430 MPa (thus,
this material is commercially called as 430 steel) Mild steel
(theoretical carbon wt % range is 0.15-0.3)
Sample B: Cold drawn (and it is called bright steel due its
finishing) Tensile strength is around 470 MPa Mild steel
(theoretical carbon wt % range is 0.15-0.3). Composition is same as
the sample A. The only difference is with the work done on the
materials.
After some lab test we could determinate the AISI value for the
sample A & B. the lab test that we need to preform are1.
Metallographic Studya. Metallographic study, or metallography, is
the imaging of topographical or microstructural features on
prepared surfaces of materials. This helps to understand the
structure o the materials2. Rockwell Hardness Testa. The Rockwell
test determines the hardness by measuring the depth of penetration
of an indenter under a large load compared to the penetration made
by a preload
3. Charpy Impact Testa. Charpy impact testing determines the
impact energy of materials.
AISI Standards are simply American Iron and Steel Institute that
has established standards for steel compositions. The two specimens
A and B were given by the supplier to familiarize ourselves in
order to find out the AISI standards of unknown samples. In AISI
standard the last two digits are the carbon content generally and
the first two digits are the series designation such as stainless
steel, high carbon, low carbon, high alloy, etc. These standards
are usually specified in order for the convenience of using
materials worldwide.
Background InformationMetallographic studyMetallographic study,
or metallography, is the imaging of topographical or
microstructural features on prepared surfaces of materials. The
structures studied by metallography are indicative of the
properties and performance of materials studied.In this technique,
planar surfaces are prepared to obtain a polished finish. Chemical
or other etching methods are often used to delineate macrostructure
and microstructure features. Once prepared, samples are examined by
the unaided eye, light microscopy, and/or electron microscopy. (See
sections on Light Microscopy and Scanning Electron
Microscopy.)Samples for microstructure evaluation are typically
encapsulated in a plastic mount for handling during sample
preparation. Large samples or samples for macrostructure evaluation
can be prepared without mounting. Sample preparation consists of
grinding and then polishing using successively finer abrasives to
obtain the desired surface finish. For microstructure examination,
a mirror finish is needed, but a finely-ground finish is adequate
for macrostructure evaluation. Etchants are specially formulated
for the specific sample material and evaluation objectives.Sampling
for metallography can be a random section to evaluate
representative bulk properties or a section in a specific location
to characterize localized material conditions. Metallographic study
can give information concerning a material composition, structure,
phase distribution, mechanical and physical properties,
thermo-mechanical process history, grain size, phase volume
fractions, and linear dimensions. Particular features of interest
are: Grain size Phases present Chemical homogeneity Distribution of
phases Elongated structures formed by plastic deformation
Grain Size DeterminationGrain size can be determined using an
intercept method described below:Straight lines all of the same
length are drawn through several photomicrographs that show the
grain structure. The grains intersected by each line segment are
counted; the line length is then divided by an average of the
number of grains intersected, taken over all the line segments. The
average grain diameter is found by dividing this result by the
linear magnification of the micrographs. Typical magnifications
used are between 50x and 1000x.
Typical applications Metal alloy heat treatment verification
Coating thickness measurement Weld or braze joint evaluation Case
hardening depth determination Corrosion resistance evaluation
Failure analysis Microscopic defects in IC devices In situ
evaluation of thermo-mechanical degradation
Rockwell Hardness Test The Rockwell tests constitute the most
common method used to measure hardness because they are so simple
to perform and require no special skills. Several different scales
may be utilized from possible combinations of various indenters and
different loads, which permit the testing of virtually all metal
alloys (as well as some polymers). Indenters include spherical and
hardened steel balls having diameters of and in. (1.588, 3.175,
6.350, and 12.70 mm), and a conical diamond (Brale) indenter, which
is used for the hardest materials.With this system, a hardness
number is determined by the difference in depth of penetration
resulting from the application of an initial minor load followed by
a larger major load; utilization of a minor load enhances test
accuracy. On the basis of the magnitude of both major and minor
loads, there are two types of tests: Rockwell and superficial
Rockwell. For Rockwell, the minor load is 10 kg, whereas major
loads are 60, 100, and 150 kg. Each scale is represented by a
letter of the alphabet; several are listed with the corresponding
indenter and load in Tables given below. For superficial tests, 3
kg is the minor load; 15, 30, and 45 kg are the possible major load
values. These scales are identified by a 15, 30, or 45 (according
to load), followed by N, T, W, X, or Y, depending on indenter.
Superficial tests are frequently performed on thin specimens. Table
below presents several superficial scales. When specifying Rockwell
and superficial harnesses, both hardness number and scale symbol
must be indicated. The scale is designated by the symbol HR
followed by the appropriate scale identification.12 For example,
80 HRB represents a Rockwell hardness of 80 on the B scale, and 60
HR30W indicates a superficial hardness of 60 on the 30W scale.For
each scale, hardnesses may range up to 130; however, as hardness
values rise above 100 or drop below 20 on any scale, they become
inaccurate; and because the scales have some overlap, in such a
situation it is best to utilize the next harder or softer
scale.Inaccuracies also result if the test specimen is too thin, if
an indentation is made too near a specimen edge, or if two
indentations are made too close to one another. Specimen thickness
should be at least ten times the indentation depth, whereas
allowance should be made for at least three indentation diameters
between the center of one indentation and the specimen edge, or to
the center of a second indentation. Furthermore, testing of
specimens stacked one on top of nother is not recommended. Also,
accuracy is dependent on the indentation being made into a smooth
flat surface.
The modern apparatus for making Rockwell hardness measurement is
automated and very simple to use; hardness is read directly, and
each measurement requires only a few seconds.
The modern testing apparatus also permits a variation in the
time of load application. This variable must also be considered in
interpreting hardness data.
Charpy Impact Test
The impact strength or commonly known as the impact strength of
a material can simply be determined using a Charpy or an Izod test.
This particular experiment used Charpy method to determine the
impact strength of both A and B under different situations. Impact
properties are not directly used in fracture mechanics
calculations, but the economical impact tests continue to be used
as a quality control method to assess notch sensitivity and for
comparing the relative toughness of engineering materials.
The two tests use different specimens and methods of holding the
specimens, but both tests make use of a pendulum-testing machine.
For both tests, the specimen is broken by a single overload event
due to the impact of the pendulum. A stop pointer is used to record
how far the pendulum swings back up after fracturing the specimen.
The impact toughness of a metal is determined by measuring the
energy absorbed in the fracture of the specimen. The height of the
pendulum times the weight of the pendulum produces the potential
energy and the difference in potential energy of the pendulum at
the start and the end of the test is equal to the absorbed energy.
Toughness is greatly affected by 1. Alloying compositions2.
Temperature (ductile to brittle transition- DBT): e.g. Titanic ship
wreck3. Heat treatments4. Strengthening mechanisms
The primary objective of metallographic examinations is to
reveal the constituents and structure of the given specimen A and
B. To determine the hardness by measuring the depth of penetration
of an indenter under a large load compared to the penetration made
by a preload the Rockwell hardness test was done on the specimen.
Finally, still most importantly Charpy impact test was done in
order to study the principles of brittle fracture in mild steels,
to understand the impact toughness of materials with different heat
and strengthening treatment and to interpret obtained experimental
data for the selection of engineering materials. Further the
objectives of the research were to get familiarize of all equipment
available to obtain ductile-brittle transition, hardness profile of
end-quenched steels and grain identification. Though these were
main objectives, the whole research was based and built on the
foundation objective of finding the AISI values of the given
specimen.
MethodologyMetallographic StudySpecimen PreparationThe
examination of materials by optical microscopy is essential in
order to understand the relationship between properties and
microstructure. Metallographic is the study of metals by optical
examination. This is most commonly done using a conventional light
microscope. However useful information can be gained by examination
with the naked eye of the surface of metal objects or of polished
and etched sections. Structures which are coarse enough to be
discernible be the naked eyes are termed macrostructures. Those
which require magnification to be visible are termed
microstructures.The preparation of a specimen to reveal its
microstructure involves. Sawing the section to be examined Mounting
in resins (if sample is too small) Coarse grinding Grinding on
progressively finer emery paper Polishing using alumina powder or
diamond paste on rotating wheel Etching in dilute acid (2% Nital
for steel)Rough PreparationThe specimen is ground on progressively
finer SiC waterproof papers from 120 to 1000 grit, to produce a
reasonably flat surface; it is lubricated with water to keep it
cool and to remove the grinding products. The sample should be
moved forward and backward on the paper until the whole surface is
covered with unidirectional scratches. It is then washed with
running water to remove debris associated with the grade of paper
used. It is then ground on the next finer paper such that the
scratches produced are at right angles to those formed by the
previous paper. This procedure is repeated through the range of
papers available.When the specimen has been ground on the final
paper, it is generally worthwhile rotating it through and grinding
again with less pressure than before. This technique can decrease
the time required for the next stage, which is polishing. Before
polishing, the specimen and your hands must be washed and dried to
remove any SiC particles.Diamond PolishingThe Diamond paste is
available in various sizes 25 m, 15 m, 10 m, 1 m, 0.5 m, 0.25 m and
if required, polishing may be started with 25 m. When the surface
is of acceptable quality, polishing is continued with diamond paste
of lower sizes. Check the appropriateness of diamond paste for the
polishing process for a particular material. In most cases two
polishing should be sufficient. This process is continued until the
fine scratches from the final paper have been removed. The specimen
and your hands, particularly finger nails, should be thoroughly
washed to remove all traces of lubricant and the 6 m diamond. The
specimen should be rinsed in alcohol and dried. After polishing,
the surface should be optically flat and should be able to use it
as a mirror. With many specimens the 1 m diamond finish will be
adequate. On occasions where it is not possible, 0.25m diamond
finishing is required.
ExaminationSpecimens should always be examined in the as
polished condition to assess the quality of polishing and to
observe any features showing contrast. After examination and noting
any features, the specimen should be etched to develop additional
contrast to reveal the microstructure.For mild steels, the specimen
must be etched for about 10-15 seconds in Nital. Analyze the
specimen under the microscope and etch for a few more seconds if
required.
Rockwell Hardness TestTest PrincipleCalculation of the hardness
number by using depth h:For spheroconical diamond indenter: HR =
100 h/0.002For ball indenter: HR = 130 h/0.002
Figure 7Rockwell Hardness Scales (not superficial):
Scale symbolPre-load kg (N)IndenterTotal test force kg
(N)Specimen material
A10 (98)Diamond (120, 0.2 tip radius)60 (589)Thin steel,
B10 (98)WC 1/16 (1.588mm)100 (981)Non-ferrous, soft steels
C10 (98)Diamond (120, 0.2 tip radius)150 (1471)Hard steels
Test piece preparation Top and bottom surfaces should be well
aligned and cleaned from any foreign matter. During preparation,
avoid heat generation, cold work etc that cause alteration of
properties. Minimum thickness, generally, should be 10 times the
depth of indentation.
Testing Conditions and Procedures Testing temperature should be
within 10-35C, and user should ensure that the test temperature
does not adversely affect the results Chose right specimen support
(flat or V-grooved) that support specimen rigidly Make certain the
crank is in unload position Chose the correct Rockwell scale
according the specimen material, hence the relevant indenter; and
total test force by using load wheel (table 1). Before start, large
pointer in the dial face should be adjusted according to the table
2 Place the specimen and bring the indenter into contact with the
test surface in a direction perpendicular to the surface of
velocity less than 2.5 mm/s by raising the anvil (slowly turn the
hand wheel clockwise). Movement of large pointer in the dial face
is the indication for proper contact Obtaining preliminary load
(10kg): continue turning the hand wheel for required number of
revolutions of large pointer according to the table 2 (over
travelling of the large pointer should be avoided). (dwell time is
0.1 to 4s) Apply load by moving the crank in to the load position
slowly (loading time is 1-8s, and dwell time is 2-6s) Unload the
specimen by moving the crank back, and read the relevant dial for
the result Always take two or more readings on each test specimen,
and get the average and round up. Minimum indentation gap is,
approximately 3 times the indented area or 2.5 times away from an
edge of the specimen Interpretation of hardness number is done by
writing the value followed by the scale. Example: 64 HRC Remove the
minor load by lowering the anvilScale symbolDial figuresLarge
pointer position (initial)Small pointer position (or # of
revolutions of large pointer)
ABlack0 or CRed spot (3)
BRed30 or B2 divisions (2)
CBlack0 or CRed spot (3)
Charpy Impact Test
Specimen Preparation
Since most of materials were anisotropic Specimen of A and B
were prepared according to preferred direction
Specimen dimensions:
55x10x10mm
A V-type notch is machined in the specimen using a notching
device shown below.
Test Preparation
Safety is to be considered at all times to protect personnel
from the swinging pendulum and flying broken specimen. Thus
students were advised to stay far from the pendulum swinging
area.
The operation-knob that controls the pendulum movement was
familiarized since for soft metals the pendulum remained
swinging.Test Procedure Check the free swing for zero in the scale
and whenever if it is not, the friction was adjusted clearly.
Mount the pendulum away by using pendulum-support in order to
provide room for the specimen mounting
Mount the specimen on the anvil by facing the notch as shown in
the following figure.
Centre the specimen by using a centering device
Raise the pendulum up to the preparation position, and lock the
pendulum
Release the pendulum by turning the operation-knob into impact
position; and obtain the impact toughness of the specimen
Finally, stop the pendulum by using the breaking system
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