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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