1 Engineering Materials Lab Report Microstructure Examination of Steel Name – Gunathilaka R

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Engineering Materials
Lab Report

Microstructure Examination of Steel

Name – Gunathilaka R.A.C.K.
ID – EN18405514
Group – Group 8 (D)
Date- 19th July 2018
Date of submission – 2nd August 2018

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1.0 Title – Microstructure Examination of Steel

2.0 Objective – To study the structure of metals by observing a microscopic view of a well prepared
steel specimen via using a conventional optical microscope.

3.0 Introduction
According to the metallography it is accompanied with studying micro and macro structures deeply by
using optical and electron microscopes. Specially electron microscopes are used to observe atomic
resolution. Some metals can be examined by naked eye because of their palpable and visible
structures.
Conventional light microscope is the most commonly used microscope. Information of grain size,
phases present, phases distribution can be provided by microscopy. In this experiment it is focused to
determine the grain size of an atomic view of a metal.
In this experiment, some chemical reagents are used to different purposes. Special machines and
equipment are necessary to complete the experiment successfully.

4.0 Theory
Intercept Method- some number of same straight lines are drawn on the photomicrographs of the
microstructure. Number of grains which are intersected by each line are counted and the length is
divided by an average of the number of grains intersected. Then a grain size is determined.
Average grain size =(Number of lines X length of each lines)
Total number of intersection

5.0 Materials and Apparatus
? 5cm x 1cm x 1cm(approximately) mild steel
? Grinding and polishing machine
? Diamond Paste- quarter of syringe
? 2 Beakers
? Dilute acid – 20 cm3
? Alcohol- 20 cm3
? Forceps-1

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6.0 Procedure

? Firstly, a proper piece of mild steel (with approximate size of given above) without rusts was
selected as a specimen to start the practical.
? Secondly, a proper face of specimen was chosen to grind and polish till it become as a mirror
surface.
? Next the grinding and polishing machine was started and set up for the optimum RPM
(Revolutions Per Minute) of 65.
? After that the chosen face of mild steel was kept on the rotating surface of grinder of grinding
and polishing machine.
? From time to time ground face of mild steel was observed since it acquires a sufficient mirror
surface.
? After getting a mirror surface, grinding and polishing machine was stopped temporarily.
? Next a small amount of Diamond Paste was added on the selected face of mild steel and the
machine was again started to continue the experiment.
? After 5 minutes’ machine was stopped.
? Two beakers separately were filled up with dilute acid and alcohol.
? Next, well ground and polished mild steel was sunk in to the dilute acid for a one minute by
using forceps.
? After that step again the specimen was sunk in to alcohol for a similar time period.
? Finally, the specimen was washed with tap water and it was observed by using an optical
microscope. Photomicrograph was used to do the further calculations.

(Mild steel specimen)

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(Grinding and polishing machine)

(Forceps) (Diamond paste)

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7.0 Observation

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8.0 Results and 9.0 Calculations

Number of lines = 5 (a, b, c, d, e)
Length of each line = 6 cm
Total number of intersections = 3+4+6+5+6 = 24

Average grain size =(Number of lines X length of each lines)
Total number of intersection
= (5X6 cm)
24 = 1.25 cm

Scale = 9.9 cm: 400 µm
Size of a grain = (400µmX 1.25 cm)
9.9 cm
=50.50 µm

Line Number of grains
1)Line – a 3
2)Line – b 4
3)Line – c 6
4)Line – d 5
5)Line – e 6

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Photomicrograph of the specimen (Mild steel)

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10.0 Discussion

10.1) There are scientific causes in some steps of procedure.
? Grinding a chosen surface of mild steel – To get a smooth mirror surface for further
observations of microscope.
? Polishing that chosen surface – To remove remained small particles and dusts.
? Adding Diamond Paste on polished surface of specimen – To remove scratches and marks
on the surface.
? Sinking in to dilute acid – To remove grease.
? Sinking in to alcohol – To neutralize the dilute acid (Because alcohol is a weak base)
? Setting the machine to 65 RPM of rotational speed – That is the optimum rotational speed to
grind and polish the specimen.
? Keeping the mild steel on same rotating direction when grinding or polishing the surface– To
get an efficient grinding and a polishing by covering a wide surface area. (Fig 1)
(Fig 1 –Mild steel is more suitable to keep on the rotating surface as the left figure because
grinding and polishing processes are efficiently done in that position)

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10.2) Possible errors and Issues –
? Specimen might have not taken a clear mirror surface after grinding.
? There could have remained scratches after polishing the specimen.
? Abrasive papers of the grinding machine may have ablated and the grinding process
may have not done properly.
? There may have been issues when counting the numbers of grains by using a
photomicrograph (Fig 2)

(Fig 2- Counting the numbers of grains is depended on the person who done the
experiment)

10.3) Assumptions –
? Specimen was ground and polished sufficiently for the experiment.
? Grease was perfectly removed after sinking the specimen in to dilute acid.
? Dilute acid was totally neutralized after sinking in to alcohol.
? Numbers of grains and boundaries were calculated accurately.

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10.4) Importance of metallography –
Metallography is simply known as the study of metals and alloys. According to the metallography
plenty of properties and microstructural features are revealed as a result of analyzing metals. Lots of
engineering applications are accomplished by metals. Furthermore, those physical properties and
qualities are identified and modified by deeply studying about the metallography. Toughness,
hardness, strength of a metal can be determined by exploring metallography. Metallography is used
to select the most suitable metal in any application. There are some techniques to reveal
microstructure of a metal, in this experiment microstructure was revealed by an optical microscope.
By using intercept method, the average size of a grain can be determined. Not only the average size
of a grain but also phases present, chemical homogeneity and distribution of phases can be
determined by using metallography. In Material Science, a precious place is allocated for
metallography.

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Conclusion
Finally, it can be deduced that the average grain size is equal to 50.50 µm by considering the results
and calculations of this experiment.

References

? Metallography.
Available from: http://www3.telus.net/BrentBeach/Sharpen/metallography.html
Accessed on 28 July 2018

? Metallography – an introduction.
Available from: https://www.leica-microsystems.com/science-lab/metallography-an-
introduction/
Accessed on 29 July 2018

? Discussion metallography is important to determine.
Available from – https://www.coursehero.com/file/p70dbs23/Discussion-Metallography-is-
important-to-determine-the-structure-of-a-material/
Accessed on 29 July 2018