Microstructure Examination of Steel PDF

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Lab Report of microstructure examination of steel...

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MT1010

Engineering Material

10.09.2020 08.10.2020

07.10.2020

Sri Lanka Institute of Information Technology

Faculty of Engineering Department of Electrical and Computer Engineering

LABORATORY REPORT

ME1010: Engineering Materials

Name: Jayasinghe H.T.K. Student ID: EN20412302 Group: 7-B

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TITLE: Microstructure Examination of Steel OBJECTIVE: •

To observe the constituents and structure of metals and their alloys by means of an optical microscope

INTRODUCTION In solid form, metals are crystalline in structure. The arrangement of the atoms which are in order and in three-dimensional pattern are internal structures and known as crystalline structure, which in the experiment is of solid metal steel. A collective of many very small crystals exits in normal metallic materials of polycrystalline and these crystals are known are the grains. Normally, these grains are very small in size and impossible to observe with bare naked eyes. There for these structural features are observed usually by microscope. Usually these features are observed by optical microscope or if possible, by an electron microscope with magnification above hundred times. These materials which require these sorts of magnification range for their analysis, are called microstructures. For an analysis of the microstructure of the metal, microscopes are the required highly. The internal structure of any material is evidentially very important in any engineering material aspect. And the structure of any material is associated with it’s arrangement, properties and performance. Mechanical, Physical and chemical properties of materials are usually determined by microstructures. Particular features such as grain size, phases present, chemical homogeneity, distribution of phases and elongated structures formed by plastic deformation obtained from microscope gives information concerning a material’s composition, previous treatment and properties. And it’s very important to understand the composition and other discussed factors of any material’s structure in real life applications. And this experiment gives us an idea of how to observe the internal structure of steel and will help in the understanding of how to observe in other materials as well. THEORY: Some detailed surface preparation should be done to reveal the important details of the microstructure of the specimen. Several steps are carried out for the preparation of the specimen. The specimen is mounted during the grinding and polishing process. The grinding is done using rotating discs grinding machine (figure 01). In the grinding machine there are various type of papers of grinding with numbers. While the number of grades is higher the amount of roughness is low. After the grinding process is over, the specimen is polished to a smooth and mirror like surface. This process is also done using the same machine but with a soft cloth. This is done due to fact that the surface unevenness to be removed. The specimen is then placed in an appropriate chemical reagent where it will attack the grain boundaries taken in the reaction. This process was done as pre-preparation for etching process. In the etching process the reagent will attack the surface of the specimen. After etching the specimen was washed with alcohol and ether to remove 3|Page

the greased layer. Grain forming can be observed under the view of microscope since they deflect at an angle different from their grains. Grain size is calculated by multiplying the number of lines (x) by the length of the line (l) and diving it by the total number of intersections (y).

𝐺𝑟𝑎𝑖𝑛 𝑆𝑖𝑧𝑒 =

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑙𝑖𝑛𝑒𝑠 (𝑥) × 𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑙𝑖𝑛𝑒 (𝑙) 𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐼𝑛𝑡𝑒𝑟𝑠𝑒𝑐𝑡𝑖𝑜𝑛 (𝑦)

MATERIAL AND APPARATUS: • • • • •

Specimen Some amount of Alcohol Optical Microscope Grinder/Polisher Machine Diamond Lapping paste

Figure 1 : Image of Grinding and Polishing machine

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Figure 2 : Image of Optical Microscope

PROCEDURE: • • • • • •

A recently grind and polished sample of specimen was obtained. Using an optical microscope and a light the cut surface of the specimen was observed. A printout of the microstructure was taken to a scale on a paper Five parallel equally length of straight lines were drawn on the printed paper. Afterwards the number of grains were counted which each line was cut through it. The counted number of grains were then summed up.

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OBSERVATION:

Figure 3:Observation sheet

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Figure 4 : Image of scaled observation of the specimen

Figure 5 : Image taken from microscope of the specimen

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CALCULATION: 𝑮𝒓𝒂𝒊𝒏 𝑺𝒊𝒛𝒆 =

5 ×5 23.5

𝑮𝒓𝒂𝒊𝒏 𝑺𝒊𝒛𝒆 = 1.064 𝑐𝑚

RESULT: Table 1 : Result data table

Line Number 1 2 3 4 5

Number of Intersection 4 5 6 4 4.5 Total Number = 23.5

Scale = 9.9cm: 400 𝜇𝑚 Grain Size = 42.983 𝜇𝑚

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DISSCUSSION: Generally, engineering materials are categorized under four basic categories such as metals, ceramics, polymers and semiconductors. Except semiconductors as they represent as functional material, the remaining three are assigned either structural or functional according to their applications. The important properties of solid material usually depend on the geometrical arrangement of their atoms and the bonding type that holds atoms together. The structure of engineering materials is considered according to the arrangement of the internal components. The atoms are arranged according to a periodical repeating array in crystalline material which is known as lattice or crystal. Microscopic level is the next largest structural level. Large number of large grouped atoms are arranged as known as microstructures and there are mostly considered as to determine the properties of the material. By studying the types of phases present in a material, it’s grain size, shape, description of their structure and the size distribution, it’s possible to have an idea of the microstructure of the material. Other than these two-dimensional defects such as heterophane interfaces and grain boundaries are important features when studying the microstructure of any material. Crystals present in the microstructure of polycrystalline materials are the grains. According to the basic crystal structure, atoms are regularly arranged within each grain. (Clemens, et al., s.d.) The phases present in the observed microstructures are grain and the grain boundaries. The phases observed was about the microstructure of the steel. There are two main structures to be considered when considering the structure of a material. Microstructure describe the appearance of the material and while crystal structure which is the other structure, describe the position of atoms in their unit cell. To the naked eye, it’s quite difficult to observe the crystalline structures. In the process of heating and melting of metal, millions of crystals are grown. When the melting is over, those crystals get cool and larger crystals. These larger crystals grown are known as the grains of the structure. There are billions of grains that have their own orientation and crystal structure in a crystalline structure. (Grade Fixer, 2019)The grain size depends on the heat treatments and materials processing and also it can be adjusted in a wide range. Metallic materials such as steels, aluminum alloys and titanium alloys have the grain size in the range of several ten micrometers. And there are Grain boundaries which refers to the areas between the grains. In the figure 4 it can be observed the grains are separated by grain boundaries. These are the second phases present in the microstructure of the specimen observed. They are the two-dimensional defects in the crystal structure. There are two types of grains called low angle and high angle grain boundaries. There difference is according to the disorientation between two grains. (Struers Ensruing Cetainty, s.d.) Metallography is the study of the structure of the metal. One of the important steps of metallography is the preparation of specimen for the examination. To obtain accurate observation and interpretation of the microstructure, the specimen should be well prepared. Selecting a sample, 9|Page

sectioning, grinding, polishing and etching are the basic specimen preparations. When selecting a sample there are some important parameters that should be considered. They are location, number and the orientation of the selecting specimen. By sectioning, grinding and polishing the surface of the specimen could have smooth and mirror like finish. When preparing the specimen, it should be done with more care in order to obtain successful microstructure interpretation. When analyzing the microstructure of steel, metallography is one of most important part. Quality controlling is the most important part in the metallography. When cutting metals, there are some side effects caused on to the metals. Due to these side effects the properties of the metal surface change and the deformed layer will be create at the surface. The deformed layers are not identical to the underlying metal. At these instance metallography is useful and the techniques of metallography helps to remove those shattered layers. In some areas microstructural testing techniques are been used. Some of them are analysis of failure, research and routing quality control. Specially microstructural analysis is used to determine whether structural parameters are within specifications. In some instances, such as heat treatment, composition or processing steps, there are some changes in microstructures. Researchers use microstructural analysis to determines these changes. Using metallography, it’s possible to determine the causes of failure of massive steel structures. (Grade Fixer, 2019) Possible errors could have been occurred during the experiment and due to that accuracy of the experiment may have decreased. To avoid these errors some precautions should have taken. It’s necessary to use new specimen of steel for the experiment. A new piece of specimen should be used because if it is old rust may have been formed. The polishing process have to be done according to required standards otherwise correct image of the microstructure may not obtain easily and correctly. Human errors can be cause during counting the intersecting grains and due to that the grain size calculated may be incorrect. CONCLUSION: The examination of microstructure provides many information about the structure of the material. It clarifies whether structural parameters are within certain specifications. Many information about properties and configuration of the microstructure are also been provided. For the evaluation of the material, results obtain from the experiment are very useful. Very important information of any crystal structure, metallic or nonmetallic structure are provided by the microstructure examination. Failure of materials is identified by microstructure examination, which are used in industries.

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References Clemens, H., Mayer, S. & Scheu, C., n.d. Wiley Online Library-Microstructure and Properties of Engineering Materials. [Online] Available at: https://onlinelibrary.wiley.com/doi/pdf/10.1002/9783527684489.ch1#:~:text=The%20grains%20in%20a %20microstructure,crystal%20defects%2C%20may%20also%20occur. [Accessed 30 September 2020]. Grade Fixer, 2019. Microstructure Examination of steel. [Online] Available at: https://gradesfixer.com/free-essay-examples/title-microstructure-examination-of-steel/ [Accessed 30 September 2020]. Struers Ensruing Cetainty, n.d. THE STRUCTURAL PROPERTIES OF METALS. [Online] Available at: https://www.struers.com/en/Knowledge/Materials/Metallic-grainstructures#characterization [Accessed 30 September 2020]. Wikipedia contributors, 2020. Microstructure. [Online] Available at: https://en.wikipedia.org/w/index.php?title=Microstructure&oldid=978359225 [Accessed 29 September 2020].

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