A Beginner's Guide to Steel Testings

ENGINEERING MATERIALS

FINAL REPORT PREPARED BY SYED RAHEEL ZAFARDHA SUFFA UNIVERSITY-

ACKNOWLEDGMENTI express my sincere thanks to Mr. Hamza Shams (Course

advisor) and Mr. Harris (Project advisor) , who guided me through the project

also gave me valuable suggestions and guidance for completing the

project. I’m also very thankful to our Mechanical Engineering department for providing us the technical support to carry out the project work.

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GRAND ASSIGNMENTObtain a 0.75 inch square rod that is 5 ft long of Mild Steel of available grade.

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Step # 1:- Preparation of SampleCutting : Cut sample(s) of 10 mm - 20 mm diameter using hacksaw or band saw and face it. For abrasive cutting use LABOTOM-5 an extremely user friendly cutting machine in which you have to clamp your piece and control your cut-off wheel through an ergonomic handle.


MountingMount sample(s) to polish/grind them. The process of compressing and heating bakelite powder around a piece of metal in order to form a solid disk or puck that can be used to handle the sample easier. Small or oddly shaped specimen are mounted to facilitate easy handling during examination. CitoPress is offering ultra-short mounting times and maximum user friendliness. On-screen Hot Mounting Application Guide for convenient information and a minimum of errors.


GrindingGrind the sample(s) to max available grit size. To get the surface for metallographic examination as optically flat, reflective and smooth scratch free. LaboPol is widely use for its friendly use, Increasing the fineness or lowering the level of abrasiveness of emery papers with the flow of water to produce finer grooves or scratches.


PolishingRubbing the specimen with an abrasive paper with some amount of liquid. Mechanized process are less time consuming and performed with ease through LaboPol in which you have to clamp your specimen and then it will rub it in opposite direction from sandpaper with some amount of liquid gel, Polishing is done automatically in a minute to two minutes time duration automatically.


EtchingIts purpose is to reveal the microstructures of a specimen under optical microscope . There are so many ways to etch but the most cheapest way is Chemical Etching in which the head of specimen is dipped in strong acid, the acid bites into the metal and contrasted the surface, usually we use Nital following are some of the most commonly used etchants

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OBJECT: From the microstructure determined in Engineering Materials Lab, label the following items on the image obtained and write briefly on their significance.1. Number of Grains2. Grain Size Number3. Average Grain SizeFrom the figure above we have calculated the Number of grains.Number of Grains at the boundary of the picture are 62, 62/2 = 31Number of Grains under the boundary are 250Total Number of grains = 250+31= 281Magnification of the above Microstructure is 400To calculate the real width/Height we use formula

Magnification = Printed Width (or) Height Real Width(or) Height

Printed width or height is the height of the image you get on A4Real Width = 274/400 = 0.685Real Height = 153/400 = 0.3825

Real Area = 0.685*0.3825 = 0.262 mm^2


N100 = {/}* Number of Grains at 400N100 = 4496

Number of Grains x Actual Area Actual Area = 0.0654 (ASTM Standard) True Area

Number of Grains = 1122.3N=By applying Log n = 11.13 Average Grain size length = Total true length / Number of grains interceptedTotal true length = Length of the lines / Magnification

L = 2 x 153 / 400 = 0.765 mmNumber of Grains intercepted = 27 (in both the lines)Avg Grain Size = 0.765/27

= 0.02833 mm


Step # 2:- Annealing of the rod.Before anneal the rod , make 4 specimens for further testing of the material.1. Two Dumbbell shaped specimens for Tensile testing, Lathe or CNC machine is highly preferred in the

manufacturing of dumbbells2. Two U notch specimens for impact testing using a rectangular rod , Milling or CNC machine is highly

preferred for cavity or adept saw user can easily make a notch.


Annealing Metals are annealed to relieve internal stresses, soften them, make them more ductile, and refine their grain structures. Metal is annealed by heating it to a prescribed temperature, holding it at that temperature for the required time, and then cooling it back to room temperature. The rate at which metal is cooled from the annealing temperature varies greatly. Steel must be cooled very slowly to produce maximum softness. This can be done by burying the hot part in sand, ashes, or some other substance that does not conduct heat readily (packing), or by shutting off the furnace and allowing the furnace and part to cool together (furnace cooling).. Annealed metals are relatively soft and can be cut and shaped more easily. They bend easily when pressure is applied. As a rule they are heated and allowed to cool slowly.


ProcedureHeating : Material is exposed to elevated temperature for an extended time period. The material is austenitized by heatingto 15 to 40 degree CelsiusSoaking : The material is held for an hour at the annealing temperature.Cooling : At room temperature it’ll be cooled at the rate of 37.8C/hr.


Results1. Relieve internal stresses and reduce the chances for cracking and distortions.2. Increasing softness and Machinability. 3. Refinement of grain structures.4. Structure will get large-grained Pearlite.

PurposeAnnealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.


Tensile Testing of Annealed SpecimenTensile testing, also known as tension testing, is a Fundamental materials science test in which a sample is subjected to a controlled tension until failure. ASTM (American Society for testing and materials) standards for this test are E8/E8MUniversal Tensile testing Machine is widely using for the Tension and compression tests of material. Specimen is fixedBetween the jaws and bring it in little tension tare it and startIncreasing load till fracture. All your valuable readings andGraphs has been observed by the system connected.


As we know annealing yields ductility and softens the materials, Our specimen has shown some correspondingResults on tensile testing under the ASTM standards E8/E8M. The graph below has been obtained by the software.


Data from the graph below. These values has been obtained through the sensors and then we scattered graph on Excel sheet

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Impact Testing of Annealed SpecimenImpact testing is of enormous importance. A collision between two objects can often result in damage to one or both of them. The damage might be a scratch, crack, fracture or break. Scientists need to know about how materials and products behave under impact and the magnitude of forces they can resist. When two objects collide, damage is often done to one or other of them. How well something resists damage is called its impact resistance. An impact test measures how much energy is absorbed when an object fractures or breaks under a high speed collision. It’s an important property. The safety of many consumer products depends on their resistance to breaking. But impact resistance is difficult to quantify. Impact testing is about resisting impact. This is often called a material’s toughness. It’s the amount of energy a material can absorb before fracturing or breaking and has the unit joules per metre cubed (J m-3). If you plot load against deflection, this energy is given by the area beneath the curve.


Two of the most popular test conducted for Impact testing is Charpy impact test and Izod impact test. I’ve carried out my test by Charpy method in which Pendulum is used, The Pendulum Impact Tester IT 30 ASTM is made by the French company Société DELTALAB. It has a pendulum hammer (mass 21.3 kg) that is 775 mm from the rotation axis. Antifriction bearings limit loss by friction to 0.75%of maximum energy. The test angle of fall is 140 degrees. Please refer to ASTM E23 to prepare your specimen or inquire your Lab Assistant for the actual specimen to take measurements. For ease of preparation we use the specimen geometry as in Fig.1. You must keep your specimen geometry constant for all investigations in this lab to compare results. During the fall from its raised position the pendulum’s potential energy decreases, changing into kinetic energy. The kinetic energy is at its greatest just before impact. This is the impact energy. The energy absorbed by the test specimen during failure (i.e. fracturing or breaking) is worked out from the height of the pendulum after impact. The specimen is placed vertically and the impact hammer strikes the Specimen above the notch and breaks it, thus this type of loading Can be considered as cantilever beam loading.


Principle of Charpy Testing


Results from Impact testingThe Energy we get is 140 Nm

Where= Load of Hammer (mass of hammer into = Distance of the hammer from the center of gravity= Angle of Fall= Angle of Rise


Hardness TestingHardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting.Hardness Test methods:Rockwell Hardness TestRockwell Superficial Hardness TestBrinell Hardness TestVickers Hardness TestMicrohardness TestMoh's Hardness TestScleroscope Hardness Test


Vickers Hardness TestThe Vickers hardness test method consists of indenting the test material with a diamond indenter, in the form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the indentation left in the surface of the material after removal of the load are measured using a microscope and their average calculated. The area of the sloping surface of the indentation is calculated. The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm area of indentation. From the above method, The length of the diagonal of cone shaped dent is 898-298 = 600The length of the second diagonal is 660-66 = 594The area is 597 nano meter square = 1.194 milli meter squareThe Vickers Hardness number is 39.02HV100


Now the broken specimen of either tensile test (dumbbell shaped) or from Charpy test (U notch) prepare for microscopy for that object we have to repeat the whole method of mounting, grinding, polishing and etching.Cut out the piece from broken specimen of the same dimensions as we did earlier and repeat the above same procedure.


As we did earlier, we’ll calculate the Number of grains, Grains Size Number, Average grain size.


From the figure above we have calculated the Number of grains.Number of Grains at the boundary of the picture are 53, 53/2 = 26.5Number of Grains under the boundary are 193Total Number of grains = 193+26.5 = 219.5Magnification of the above Microstructure is 400To calculate the real width/Height we use formula



Real Area = 0.685*0.3825 = 0.262 mm^2N100 = {/}* Number of Grains at 400N100 = 3512

Number of Grains = Actual Area Actual Area = 0.0654 (ASTM Standard) True Area

Number of Grains = 877N=By applying Log you can get your desired value


n = 10.8 11Now Draw two lines parallel to each other at some distanceHeight of both the lines are 153mm as of the image Average Grain size length = Total true length / Number of grains interceptedTotal true length = Length of the lines / Magnification


= 0.0255mm


Talking Points• Steel must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further

work such as shaping, stamping, or forming.• Material’s ductility has been increased so its tensile strength increased and it will produce some

elongations as necking


Heat Treatment and Quenching


Conventional heat treatment procedures for producing martensitic steels typically involve continuous and rapid cooling of an austenitized specimen in some type of quenching medium, such as water, oil, or air. The optimum properties of a steel that has been quenched and then tempered can be realized only if, during the quenching heat treatment, the specimen has been converted to a high content of martensite; the formation of any pearlite and/or bainite will result in other than the best combination of mechanical characteristics. During the quenching treatment, it is impossible to cool the specimen at a uniform rate throughout—the surface always cools more rapidly than interior regions. Therefore, the austenite transforms over a range of temperatures, yielding a possible variation of microstructure and properties with position within a specimen. The successful heat treating of steels to produce a predominantly martensitic microstructure throughout the cross section depends mainly on three factors: (1) The composition of the alloy.(2) The type and character of the quenching medium.(3) The size and shape of the specimen. The influence of each of these factors is now addressed.


Quenched specimens ready for the Tensile testing.


Tensile Testing of Water Quenched Specimen


As we did earlier this test had also been carried out in similar way.

Quenching hardened the steel soIt directly affects the tensile test.Annealed specimen has UTS around400 MPa and this specimen has shown strength.


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Tensile Test of Quenched Specimen

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The failure leads to ductility because the shear angle is still not zero degree but not at 45 degree as well, quenching hardened the material so the material has lost some of its ductility and gained brittleness. We can understand this result by comparing both of the the annealed and quenched samples through tensile testing, We can easily observe the huge variation in Ultimate tensile strengths of both samples and similarly the shearing angle of both the specimens have some difference. The annealed specimen is pure shear at 45 and quenched specimen is broken at less than 45


Impact Test of Quenched SpecimenWe can expect the result of Impact test before conducting it, as quenching yields hardenability so the Value of hardness will be much more greater than the annealed one.By going through the similar method as we did above in annealed case.Energy or Toughness = 161 Nm

Hardness Test of Quenched Specimen571-205 = 366535-168 = 367Area = 366.5 = 366.5*0.002 = 0.733Hardness = 104.68 HV100


Microstructure of Quenched Specimen


From the figure above we have calculated the Number of grains.Number of Grains at the boundary of the picture are 66Number of Grains under the boundary are 229Total Number of grains = 229 + 66/2 = 229 + 33 = 262Magnification of the above Microstructure is 400To calculate the real width/Height we use formula



Real Area = 0.685*0.3825 = 0.262 mm^2N100 = {/}* Number of Grains at 400N100 = 4192

Number of Grains = Actual Area Actual Area = 0.0654 (ASTM Standard) True Area

Number of Grains = 1046.4N=By applying Log the Grain Size number is 11.01


Average Grain size length = Total true length / Number of grains interceptedTotal true length = Length of the lines / Magnification


= 0.02125mm


Talking Points• Quenching can reduce the crystal grain size of both metallic and plastic materials, increasing their

hardness.• Extremely rapid cooling can prevent the formation of all crystal structure, resulting in amorphous metal

or "metallic glass".• An iron or steel alloy will be excessively hard and brittle due to an overabundance of Martensite after

quenching.

https://en.wikipedia.org/wiki/Amorphous_metal