ABSTRACT

The experiment was conducted to understand the procedure metallographic

sample preparation and perform analysis from the microstructure’s observation.

Furthermore, the experiment was conducted to understand basic function of optical

microscope and its operation. Lastly, to understand the theoretical background of

sample preparation and metallographic specimens. During the experiment, six process

was conducted which are cutting, moulding, grinding, polishing, etching and

metallographic observation. From metallographic observation, the result can be

obtained which is the grain structure of ferrite and pearlite.

TABLE OF CONTENT

# Contents Page

1 Abstract

2 Table of Content

3 List of Figures

4 Introduction

5 Theory

6

Experimental Procedures

List of Apparatus

Cutting

Moulding

Grinding

Polishing

Etching

Observation Under an Optical Microscope

7 Results

8 Discussion

9 Conclusion

10 References

LIST OF FIGURE

# Figures Page

1 Abrasive cutter machine

2 Automatic mounting press machine

3 Grinding machine

4 Polishing machine

5 Fume chamber

6 Optic Microscope

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Results :

Microstructure of Low-Carbon Steel Under a Magnification of :

M5

M10

M20

M40

INTRODUCTION

In the study of metallic materials, it is often to analyze the phases exist and

grain size in the structure. Details of the structure of metals are not readily visible

through naked eyes, but grain structures in metal may be seen with the aid of

microscope. Metal characteristic such as grain sizes, effects of heat treatment, and

carbon content of steels may be determined by studying the micrograph. For this

purpose, the metal used in the metallurgical examination must be prepared and

polished carefully before a good microscopic image can be seen. It is important to

ensure that the surface is totally flat and smooth before microstructure observation.

Any irregularity will appear as a dark image and may create confusion to the observer

who attempts to analyze a structure. In order to obtain this smooth flat surface, several

preparatory steps are required which are cutting, moulding, grinding, polishing, and

etching. After that, the specimen can be analysed under the optical microscope.

Cutting

In order to get the desired size of the sample so that it can be easily moulded and

handle, the cutting process is carried out.

Moulding

Moulding process is carried out to make the sample easier to hold throughout the

experiment. There are two types of moulding process which are hot moulding and

cold moulding.

Grinding

To remove rough surface, grinding process was carried out. There are two process

which are rough grinding and fine grinding. Rough grinding purpose is to remove

rough scale on the surface of sample. Another one is fine grinding that purpose to

improve the specimen’s surface until it begins to shine and reflect light slightly.

Etching

Etchants are used to selectively attack the surface of metals to reveal grain

boundaries, phase, precipitates, inclusion and variations in composition.

Metallographic Observation

The structure can be observed with the aid of optical microscope after mirror-like

metal surface has been obtained during the etching process. The optical microscope

magnifies an image by sending a beam of light through the object. The lens then

focuses the light on the sample and objective lens magnifies the beam which contain

the image so the image can be seen by the observer.

THEORY

In this experiment, there are several processes that need to be done. In order to

obtain the best result which is smooth flat surface, several preparatory steps are

required. The processes are cutting, moulding, grinding, polishing and etching.

First of all, cutting process needs to be done. This process is been made to get

the required size of the specimen. In this process, abrasive cutting machine is used to

avoid any alteration in the microstructure of the specimen. Abrasive cutting machine

is the best solution since this process has many advantages. The advantages are :

extremely clean and fast

excellent quality of the cut-off material

quick and easy retooling

minimum noise level

cutting of the work piece in hot or cold state

flexible machine conception - proven design also for flat foundations

dry cutting without emulsion for almost all applications

The second process is moulding. Moulding is the process of manufacturing by

shaping liquid or pliable raw material using a rigid frame called a mold or matrix.

This itself may have been made using a pattern or model of the final object.

Compressible mounting resins area available in different colour and also with various

filters for different types of hardness. Mounting process can be divided into two

process : Cold Mounting and Hot Mounting. In cold mounting, 10gm epoxy resin and

1gm of hardener are mixed together and pour into mould for 24 hour. Cold mounting

will result in clear mould cover. Hot mounting will result in red or black mould cover.

The advantages of moulding are :

Easier to hold the specimen

Provide protection to the edges

Enable to label and store the specimen

Provide standard format to mount multiple specimen (colour

categories)

The next process is grinding. Grinding process can be divided into two types :

Coarse grinding and fine grinding. The purpose of coarse grinding process is to

remove the scratch that has been formed from cutting and mounting process. In coarse

grinding, it is done with wet surface using 240, 320 and 400 grit electrically powered

disc. On the other hand, the purpose of fine grinding is simply for finishing. In fine

grinding, the process must be done with careful to avoid any additional scratches that

can cause the microstructure of the specimen is damage. Wet operation is also used in

fine grinding to avoid any side effects such as excess heating. It is done using finer

abrasive which is 600 and 1200 grits. In both coarse and fine grinding, the specimen

must be held constant during the grinding at any stage.

The next process is polishing. The powder used in this experiment is aluminar

powder. Before proceed to this process, the specimen must be fully dried because the

surface of the specimen may scratch if it has been contaminated by any unwanted

material even the smallest hard dust. In this process, light pressure is applied with

slow speed of rotating wheel. Polishing is also can be divided into two types : Rough

polishing and Fine polishing. Rough polishing used 9.5 micron and 5 micron stage

while fine polishing used 3 micron and 1 micron stage. The polishing stage is already

completed if the specimen indicates a mirror-like surface free of scratches.

The final process in this experiment is etching. Etching is the process of

highlighting and identifying micro structural features. The process is done by dipping

the specimen to the chemicals for several seconds. The etchant used is called nital :

the mixture of nitric acid and alcohol. The surface of the specimen must not be

touched after this process to avoid any damage to the microstructure of the specimen.

If the visual under microscope is blurring, it means that the specimen is under etching.

It has to undergo the etching process for another several seconds. If the visual under

microscope is dark, it means that the specimen is over etching. It has to undergo the

polishing process followed by etching process once again.

After the 5 processes are complete, the specimen microstructure can be

examined by the microscope to observe it metallographic condition. The resolution of

the field can be adjusted starting with magnification of M5, M10, M20 and M40.

APPARATUS

Figure 1:

Abrasive Cutter Machine

Figure 2:

Automatic Mounting Press Machine

Figure 3:

Grinding Machine

Figure 4:

Polish

Machine

Figure 6:

Optic Microscope

Figure 5:

Fume Chamber

PROCEDURE

Cutting

1. The specimen is measured and marked.

2. The specimen has been clamped at the cutting area.

3. The cover of the abrasive cutter is closed.

4. The water and pump is opened and the machine switch is turned on.

5. Slowly lowered the cutter towards the specimen by using hand.

6. After the process is finished, the entire switch been turned off and the cover of

the abrasive cutter is opened.

7. The specimen is unclamped and proceeds to moulding process.

Hot moulding

1. Specimen was cleaned to remove cutting and handling residues.

2. Debris was removed from mould assembly.

3. Thin coat of mould release compound was applied to mould assembly.

4. Mould ram was raised to up position.

5. The specimen was centred on ram

6. The ram assembly was lowered.

7. One and a half of small cups of phenolic powder were poured into mould.

8. Any excess phenolic powder was cleaned and removed from around the mould

assembly threads.

9. Mould assembly cover was locked.

10. Ram was slowly raised into up position approximately 10 minutes.

11. 180°C heat and 200 bar pressure was applied for specific period of time.

12. The sample was cooled to near room temperature.

13. Mounted specimen was removed.

14. Mould and ram assembly was cleaned.

Grinding

(a) Rough Grinding

1. The specimen was labelled.

2. The motor was turned on, then the water.

3. Grinding started with the 240 grit sand paper and both hands was used to hold

the specimen.

4. The sample face was carefully places onto the exposed area of the sand paper.

5. Moderate pressure was applied evenly.

6. The sample was hold statically to achieve uniform surface of sample.

7. Both hands used to hold the specimen.

8. All scrap was washed carefully from sample using tap water when all the

sample's scratches were parallel.

9. The specimen then dried immediately using paper towel to avoid corrosion.

10. The 320 and 400 grit sand paper was used for the next step in coarse grinding.

11. Step 2 to 5 was repeated until the specimen achieve smooth surface.

12. When the 320 and 400 grit stages was completed, the processes then proceed

to the medium or fine grinding.

(b) Fine Grinding

1. The step was quite the same with rough grinding, but the fine surface of the

specimen is the actual aim of this process.

2. Started with the lowest grade of sand paper, 600 grit, and proceed to the

highest, 1200 grit.

3. Fine grinding was continued until the previous stage's scratches were gone.

4. A few extra strokes were used to complete scratch removal. The specimen was

carefully rinsed after each step of fine grinding.

5. The specimen then was rinsed thoroughly before proceeding to polishing.

Polishing

1. The specimen and hand were ensured have been thoroughly cleaned before

polishing.

2. Polishing started with the 4-micron.

3. A small amount of the aluminium oxide abrasive solution was applied to the

polishing cloth.

4. During polishing, the specimen was hold with both hands.

5. A moderate amount of pressure was applied. The rough polishing stages took

1 and 2 minutes each.

6. The specimen was washed and dried thoroughly then rinse before proceeding

to the next polishing stage.

7. Step 3 to 5 was repeated for the 3-micron stage.

8. The specimen was hold with both hands and a small amount of pressure was

applied.

9. The final polishing stage took between half or 1 minute. The wheel was

covered when it is not in used.

10. The specimen were washed and dried then rinsed with distilled water before

proceeding to etching.

Etching

1. The specimen was placed on the table under the fume hood with the polished

surface up.

2. The fume hood was turned on.

3. The surface was cleaned with distilled water and let dried using the

pressurized air.

4. An etchant solution was poured in the lab dish.

5. The specimen was dipped in the etchant solution.

6. After 5 to 10 seconds. The etchant was rinsed into the sink with the water and

it is quickly rinsed with water.

7. The sample was dried using pressurized air.

8. The process then was proceeds to microscopic examination.

Metallographic Observation

1. The sample was examined in the microscope. Initially the specimen was examined

through the stereomicroscope that gave a three-dimensional impression of the

specimen surface. With a properly etched specimen, grains were differentiated and

impurity particles could be seen clearly.

2. Metallurgical microscope was used to view the specimen at various magnifications

and the micro structural aspect of the material was noted.

3. The microstructure of the specimen was sketched.

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REFERENCES

1. George F. Vander Voort, “Macroetchants for Revealing Strain Patterns”,

Metallography, Principles and Practise, ASM International, New York, 1984, pp.9

2. G. Petzow, “Metallographic Preparation”, Metallographic Etching, 2nd Edition,

ASM International, New York, 1999, pp.209

3. ASM, “Metallography and Microstuctures”, ASM Metals Hand Book, 9th Edition,

Metals Park, New York, 1983, pp.228

4. Norman Emme Woldman, “Preparation and Microscopic Examination of a

Specimen”, Physical Metallurgy, Chapman & Hall, London, 1930, pp.14

5. http://www.substech.com/dokuwiki/doku.php?id=etching_metallographic_specimens

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