TERM PAPER

MATERIAL SCIENCE

MEC-208

TOPIC:-WHAT IS THE IMPORTANCE OF MICROSTRUCTURES, WRITE A REPORT ON MICROSTRUCTURES OF CAST IRON.

SUBMITTED TO:- SUBMITTED BY:-

MR.PIYUSH CHAND VERMA RAJESH KUMAR(DEPTT.OF MECH. ENGG.) REGD. NO:-10904731

CLASS: - B.TECH (ME)

ROLL NO: - A27

SECTION:- B4912

ACKNOWLEDGEMENT

As usual a large number of people deserve my thanks for the help

they provided me for the preparation of this term paper.

First of all I would like to thank my teacher MR.PIYUSH CHAND

VERMA “Sir” for his support during the preparation of this topic. I am

very thankful for his guidance.

I would also like to thank my friends for the encouragement and

information about the topic they provided to me during my efforts to

prepare this topic.

At last but not the least I would like to thank seniors for providing me

their experience and being with me during my work.

THANK YOU Rajesh kumar

INTRODUCTION

THE examination of microstructure is one of the principal means of evaluating alloys and products to determine the effects of various fabrication and thermal treatments and to analyze the

cause of failure. Main microstructural changes occur during freezing, homogenization, hot or cold working, annealing, etc. Good interpretation of the structure relies on having a complete history of the specimen. In general, the metallography of metals and metallic alloys is a hard job in the meaning that materials represent a great variety of chemical compositions and thus a wide range of hardness and different mechanical properties. Therefore the techniques required for metallographic examination may vary considerably between soft and hard alloys. Moreover, one specific alloy can contain several microstructural features, like matrix, second phases, dispersoids, grains, sub grains and thus grain boundaries or sub boundaries according to the type of the alloy and its thermal or thermo mechanical history. However, some methods of sample preparation and observation are quite general and apply to all such materials.As a general rule, examination should start at normal eye vision level and proceed to higher magnification. Simplicity and cost make optical examination (macro and micro) the most useful. When the magnification and the depth of focus become too low, the electron microscopes are required.

[1] INTRODUCTION TO MICROSTRUCTURE

Microstructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification. The microstructure of a material (which can be broadly classified into metallic, polymeric, ceramic and composite) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior, wear resistance, and so on, which in turn govern the application of these materials in industrial practice.

[2] WHAT IS MICROSTRUCTURE?When describing the structure of a material, we make a clear distinction between its crystal structure and its microstructure. The term ‘crystal structure’ is used to describe the average positions of atoms within the unit cell, and is completely specified by the lattice type and the fractional coordinates of the atoms (as determined, for example, by X-ray diffraction). In other words, the crystal structure describes the appearance of the material on an atomic (or Å) length scale. The term ‘microstructure’ is used to describe the appearance of the material on the nm-cm length scale. A reasonable working definition of microstructure is:

“THE ARRANGEMENT OF PHASES AND DEFECTS WITHIN A MATERIAL.”

Microstructure can be observed using a range of microscopy techniques. The microstructural features of a given material may vary greatly when observed at different length scales. For this reason, it is crucial to consider the length scale of the observations you are making when describing the microstructure of a material.

When describing the structure of a material, we make a clear distinction between its crystal structure and its microstructure. The term ‘crystal structure’ is used to describe the average positions of atoms within the unit cell, and is completely specified by the lattice type and the fractional coordinates of the atoms (as determined, for example, by X-ray diffraction). In other words, the crystal structure describes the appearance of the material on an atomic (or Å) length scale. The term ‘microstructure’ is used to describe the appearance of the material on the nm-cm length scale. A reasonable working definition of microstructure is: Microstructure can be observed using a range of microscopy techniques.

The microstructural features of a given material may vary greatly when observed at different length scales. For this reason, it is crucial to consider the length scale of the observations we are making when describing the microstructure of a material. In this course we will learn about how and why microstructures form, and how microstructures are observed experimentally. Most importantly, microstructures affect the physical properties and behavior of a material, and we can tailor the microstructure of a material to give it specific properties (this is the subject of the next course). The microstructures of natural minerals provide information about their complex geological history. Microstructure is a fundamental part of all materials and minerals science, and these themes will be expanded on in subsequent courses. This practical is in three parts.

[3] WHY IS THE MICROSTRUCTURE OF A MATERIAL IMPORTANT?

The most important aspect of any engineering material is its structure. The structure of a material is related to its composition, properties, processing history and performance. And therefore, studying the microstructure of a material provides information linking its composition and processing to its properties and performance. Interpretation of microstructures requires an understanding of the processes by which various structures are formed. Physical Metallurgy is the science which provides meaningful explanations of the microstructures, through understanding what is happening is inside a metal during the various processing steps. Metallography is the science of preparing specimens, examining the structures with a microscope and interpreting the microstructures. The structural features present in a material are a function of the composition and form of the starting material, and any subsequent heat treatments and or processing treatments the material receives. Microstructural analysis is used to gain information on how the material was produced and the quality of the resulting material. Microstructural features, such as grain size, inclusions, impurities, second phases, porosity, segregation or

surface effects, are a function of the starting material and subsequent processing treatments. The microstructural features of metals are well defined and documented, and understood to be the result of specific treatments. These microstructural features affect the properties of a material, and certain microstructural features areassociated with superior properties.

[4] WHAT IS MICROSTRUCTURAL ANALYSIS USED FOR?Microstructural and microstructural examination techniques are employed in areas such as routine quality control, failure analysis and research studies. In quality control, microstructural analysis is used to determine if the structural parameters are within certain specifications. It issued as a criterion for acceptance or rejection. The microstructural features sometimes considered are grain size, amount of impurities, second phases, porosity, segregation or defects present. The amount of size of these features can be measured and quantified, and compared to the acceptance criterion. Various techniques for quantifying microstructural features, such as grain size, particle or pore size, volume fraction of a constituent, and inclusion rating, are available for comparative analysis. Microstructural analysis is used in failure analysis to determine the cause of failure. Failures can occur due to improper material selection and poor quality control. Microstructural examination of a failed component is used to identify the material and the condition of the material of the component. Through microstructural examination one can determine if the component was made from specified material and if the material received the proper processing treatments. Failure analysis, examining the fracture surface of the failed component, provides information about the cause of failure. Failure surfaces have been well documented over the years and certain features are associated with certain types of failures. Using failure analysis it is possible to determine the type of stress that caused the component to fail and often times determine the origin of the fracture. Microstructural analysis is used in research studies to determine the microstructural changes that occur as a result of varying parameters such as composition, heat treatment or processing steps. Typical research studies include microstructural analysis and materials property testing. Through these research programs the processing - structure - property relationships are developed.

[5] HOW MICROSTRUCTURES FORM?

Microstructures form through a variety of different processes. Microstructures are almost always generated when a material undergoes a phase transformation brought about by changing temperature and/or pressure (e.g. a melt crystallizing to a solid on cooling). Microstructures can be created through deformation or processing of the material (e.g. rolling, pressing, welding). Finally, microstructures can be created artificially by combining different materials to form a composite material (e.g. carbon-fiber reinforced plastic). Here we will examine some examples of microstructures formed by different processes. The materials will be examined using both reflected-light and transmitted-light microscopes. Ask your demonstrators for advice on setting up the two different types of microscope. Guidelines are printed on separate sheets. Remember to look at the materials at a range of magnifications: some microstructural details may only be visible at high magnification![A] SOLIDIFICATION. Solidification of a crystal from a melt occurs through a process ofNucleation and growth. Below the freezing temperature, small clusters of atoms in the melt come together through random chance to form a small crystalline particle (a nucleus). The nucleus

forms a template onto which other atoms can attach. Each nucleus grows into an individual grain of the crystal. When adjacent grains impinge they form grain boundaries. Since individual nuclei form in different orientations, there is no orientation relationship between adjacent grains. When a melt with limited miscibility between components solidifies, one often finds that different phases solidify at different temperatures on cooling. In some cases, the different phases form contemporaneously and become intimately intergrown with each other to form complex (and often quite beautiful) microstructures. We will meet many examples of this behavior throughout this course.

[B] PHASE SEPARATION (EX-SOLUTION, PRECIPITATION). A multi-component material can exist as a single phase if the components are intimately mixed (i.e. miscible) at the atomic scale (forming a solid solution). In many materials, miscibility is restricted to a limited range of compositions. The range of miscibility is a strong function of temperature: a material that is happy to form a single phase at high temperature might be forced to unmixed into two phases at lower temperature (i.e. the components become immiscible). This process is known as phase separation, ex-solution or precipitation. We have already seen a classic example of this phenomenon in the case of the Fe-Ni meteorite.When a melt with limited miscibility between components solidifies, one often finds that different phases solidify at different temperatures on cooling. In some cases, the different phases form contemporaneously and become intimately intergrown with each other to form complex (and often quite beautiful) microstructures. We will meet many examples of this behaviour throughout this course.

[6] PHASE/COMPONENT/DEFECT

A ‘phase’ is taken to be any part of a material with a distinct crystal structure and/or chemical composition. Different phases in a material are separated from one another byDistinct boundaries. A pure substance with a uniquely-defined chemical composition is said to consist of one chemical ‘component’. The chemical composition of some materials can be varied continuously between two or more extremes (often referred to as ‘end members’). These materials must contain, therefore, two or more chemical components. Note that a multicomponent material can exist as a single phase if the different chemical components are intimately mixed at the atomic length scale. In the solid state, such mixtures are called ‘solid solutions’.

A ‘defect’ is taken to mean any disruption to the perfect periodicity of the crystal structure. This includes point defects such as vacancies and interstitials, planar defects such as surfaces, twin boundaries, and grain boundaries, and as we will investigate in Course D, dislocations.

(a) A single crystal of quartz (SiO2)(b) A sheet of galvanized steel (Zn surface layer)(c) An Fe-Ni meteorite(d) A partially crystallized wollastonite (CaSiO3) glass(e) GraniteYou are provided with several photographs and hand specimens. In each case, writedown the number of components and phases present, and identify the types of defect (if any) that are present. Make a labeled sketch of each one and add an appropriate scale bar.

[7] METALLOGRAPHY

Metallography is the science and art of preparing a metal surface for analysis by grinding and polishing, and etching to reveal the structure of the specimen. Ceramic, sintered carbide or any other solid material may also be prepared using metallographic techniques, hence the collective term, materialography.

HENRY CLIFTON SORBY (1826–1908), FOUNDER OF METALLOGRAPHY

Metallographic and materialographic specimen preparation seeks to find the true structure of the material. Mechanical preparation is the most common method of preparing the specimens for examination. Abrasive particles are used in successively finer steps to remove material from the specimen surface until the needed metallographic surface quality is achieved. A large number of materialographic preparation machines for grinding and polishing are available, meeting different demands on preparation quality, capacity, and reproducibility. A systematic preparation method is the easiest way to achieve the true materialographic structure.When the work routinely involves examining the same material, in the same condition, themetallographer wants to achieve the same result each time. This means that the preparation result must be reproducible. Different materials with similar properties (hardness and ductility) will respond alike and thus require the same consumables during preparation. Specimen preparation must therefore pursue rules which are suitable for most materials.

[8] SAMPLE PREPARATION

A properly prepared metallographic sample can be aesthetically pleasing as well as revealing from a scientific point of view. The purpose of this is to understand how to prepare and interpretmetallographic samples systematically.

[9] CUTTING METALLIC SAMPLES

This was done using a hacksaw which is made of secondary-hardened tool steel. Although the blade is significantly flexible, it is very hard and can fracture violently if the direction of the strokedeviates much from the plane of the cut.

To use the hacksaw, the sample must be secured in a vice; obviously, the plane of the cut must contain the direction of the gripping force.

SAMPLE MOUNTINGSmall samples were difficult to hold safely during grinding and polishing operations, and their shape was not suitable for observation on a flat surface. They were therefore mounted inside a polymer block.

For mounting, the sample is surrounded by an organic polymeric powder which melts under the influence of heat (about 200 oC). Pressure was also applied by a piston, ensuring a high quality mould, free of porosity and with intimate contact between the sample and the polymer.

PHENOLIC POWDER AND MOULD RELEASE

Agent: Phenolic powder was used as the mould under 7 Bar of pressure at approximately around 160 oC. The finished mount, for better results was ejected after it was cooled down under pressure to below 30 oC from the press.

Mould release agent was sprayed prior to compression mounting to make sure that the prepared mould does not stick to the surfaceof mounting press.

MOULD MAKING MACHINE

Mould making machine or a Mounting press was used to obtain the mould for specimen to be used for further operations on mould like grinding or polishing. Regardless of the resin used to compression mount specimens, the best results are obtained when:[1] The specimen are clean and dry [2] The cured mounts are cooled under full pressure below 30 oC before ejection from the press.

GRINDING AND POLISHING

Grinding was done using rotating discs covered with silicon carbide paper and water. There are a number of grades of paper, with 180, 240, 400, 800, 1200, 1500, 2000 grains of silicon carbide per square inch. 180 grade therefore represents the coarsest particles and this is the grade to begin the grinding operation.

Grinding Machine Polishing MachineAlways use light pressure applied at Centre of the sample. Continue grinding until all the blemishes have been removed, the sample surface is flat, and all the scratches are in a single orientation. Wash the sample in water and move to the next grade, orienting the scratches from the previous grade normal to the rotation direction. This makes it easy to see when the coarser scratches have all been removed. After the final grinding operation on 2000 paper, wash the sample in water followed by alcohol and dry it before moving to the polishers. The polishers consist of rotating discs covered with soft cloth impregnated with diamond particles (6 and 1 micron size) and an oily lubricant. Begin with the 6 micron grade and continue polishing until the grinding scratches have been removed. It is of vital importance that the sample is thoroughly cleaned using soapy water, followed by alcohol, and dried before moving onto the final 1 micron stage. Any contamination of the 1 micron polishing disc will make it impossible to achieve a satisfactory polish.

ETCHINGThe purpose of etching is two-fold.[1] Grinding and polishing operations produce a highly deformed, thin layer on the surface which is removed chemically during etching.[2] Secondly, the etchant attacks the surface with preference for those sites with the highest energy, leading to surface relief which allows different crystal orientations, grain boundaries, precipitates, phases and defects to be

distinguished in reflected light microscopy

.

[10] Microscopy

Abbe theory of imaging and resolution

we have met the principles of diffraction from lattice planes in Course A. Here we revisesome of the basic concepts and how they relate to the formation of images in a transmission electron microscope (TEM). We will then use the laser benches to explore the resolution of a system. The basic principles of image formation in a microscope (either an optical or anelectron microscope) are illustrated in Fig. 1.

Fig. 1. Abbe theory of imaging using all diffracted spots

Radiation with wavelength λ is incident on the object (in this case a diffraction grating with slit spacing d). Each slit in the grating scatters radiation in a variety of directions. Radiation scattered in a given direction is collected by a lens placed at a distance u from the object and focused into a point in the back focal plane, located at a distance f from the lens. If the condition dsin = n is satisfied then constructive interference occurs and a bright diffraction spot will appear at that point. The image is formed at a

distance v from the lens. The image can be considered as the diffraction pattern of the diffraction pattern in the back focal plane.

An image is formed when the equation:1/u + 1/v = 1/fis satisfied. Here f is the focal length of the lens.

OBSERVATION OF DIFFRACTION GRATINGS IN AN OPTICAL MICROSCOPE

Transmitted light microscopes are set up on a side bench to examine diffraction gratings of different spacing’s. When making these observations, it is important that none of the settings of the microscopes are changed except as indicated below.Three diffraction gratings are set in a single mount. Observe the grating with widestspacing (100 lines/mm) taking care to focus precisely. Next look at the 300 lines/mm grating and determine whether the lines are resolvable. (Any adjustment to the focus should be extremely slight.) With all the settings untouched, carefully remove the microscope eyepiece and look down the tube with the eye several inches away from it. This gives a view of the back focal plane of the microscope. Observe and sketch the diffraction pattern.

With the eyepiece still removed, move the 100 lines/mm grating under the objective. (Note: under some circumstances this pattern can be difficult to see at first. It can help to move the eyefrom side to side.)Finally, observe both the diffraction pattern and the image of the fine grating (600 lines/mm). Are the lines resolvable, and could they be if the quality of the lens system was improved? From all your observations, estimate the resolution of the microscope as set up.Compare this with the theoretical limit of resolution, dmin, for an optical microscope.

which is given by

where is the wavelength of light (~0.5 μm), n is the refractive index of the medium between the specimen and the objective lens (n ≈ 1 for air), and α is the acceptance angle of the objective lens. The value of n sin α is usually printed on the side of each lens as the numerical aperture, N. A.Essentially the microscope is a tube whose diameter puts a maximum limit on the orders of diffraction maxima which manage to exit the tube to form an

image. Making the tube wider increases the maximum resolution, but then the larger lenses suffer from more aberrations which in turn need correction.

WARNING: LASER LIGHT IS VERY BRIGHT

The He-Ne lasers you will be using are of comparatively low power, nominally 0.5 mW, and thus not particularly dangerous. The intensity of the light in the main laser beam is similar to sunlight, and thus the damage which it could inflict on the retina is closely equivalent to that which would result from forcing oneself to look directly into the sun. For this reason never look along the laser beam and be careful to prevent it from reaching anybody else in the laboratory.Images formed from a single diffraction spot will not contain any informationabout the periodicity of the object (i.e. its crystal structure), but they will containinformation about the general shape, size, and spatial distribution of phases anddefects in the object (i.e. its microstructure).Images formed from all the diffraction spots are high resolution images whichallow us to visualise the periodicity of the underlying crystal structure.‘Low’ magnification scanning electron microscope images of two-phase intergrowths in etched limonite-hematite. Dark patches show where hematite lamellae have been preferentially dissolved out of the limonite host. (b) ‘Medium’ magnification image of a dissolved hematite lamella, which itself contained finer-scale ilmenite platelets.‘High’ magnification transmission electron microscope image of hematite Platelets in an ilmenite host. Note that length scale of platelets decreases from left to Right, with sizes reaching 1-2 nm (the unit cell length of hematite is 1.4 nm

[11] MICROSTRUCTURE ANALYSIS OF GRAY CAST IRON

Grey iron is a cast iron alloy that has a graphitic microstructure. It’s named after the gray color of the fracture it forms, which is due to the presence of

graphite. Grey cast irons are softer with a microstructure of graphite in transformed-austenite and cementite matrix. The graphite flakes, which are rosettes in three dimensions, have a low density and hence compensate for the freezing contraction, thus giving good castings free from porosity. The flakes of graphite have good damping characteristics and good machinability. In applications involving wear, the graphite is beneficial because it helps retain lubricants. Sulphur in cast irons is known to favour the formation of graphite flakes. The graphite can be induced to precipitate in a spheroidal shape by removing the sulphur from the melt using a small quantity of calcium carbide. This is followed by a minute addition of magnesium or cerium, which poisons the preferred growth directions and hence leads to isotropic growth resulting in spheroids of graphite. The calcium treatment is necessary before the addition of magnesium since the latter also has an affinity for both sulphur and oxygen, whereas its spheroidising ability depends on its presence in solution in the liquid iron. The magnesium is frequently added as an alloy with iron and silicon (Fe-Si-Mg) rather than as pure magnesium. However, magnesium tends to encourage the precipitation of cementite, so silicon is also added (in the form of ferro-silicon) to ensure the precipitation of carbon as graphite. The ferro-silicon is known as an inoculant. Spheroidal graphite cast iron has excellent toughness and is used widely, for example in crankshafts.

GRAPHITIZATION

A solid-state transformation of thermodynamically unstable non-graphitic carbon into graphite by means of heat treatment.

Properties of grey cast-Iron

TYPICAL USES

Cast iron is used in a wide variety of structural and decorative applications, because it is relatively in expensive, durable and easily cast into a variety of shapes. Most of the typical uses include:

[1] Historic markers and plaques[2] Hardware: hinges, latches[3] Columns, balusters[4] Stairs[5] Structural connectors in buildings and monuments[6] Decorative features[7] Fences[8] Tools and utensils[9] Stoves and firebacks[10] piping

[12] STANDARD MICROSTRUCTURES OF GRAY CAST IRON

As-cast gray iron (Fe-2.8%C-0.8%Si-0.4%Mn-0.1%S-0.35%P-0.3%Cr). Pearlite Etched with 4% nital. Arrows show the white areas with weakly etched or non-etched pearlite, 500X.

As-cast gray iron, (Fe-3.24%C-2.32%Si-0.54%Mn-0.71%P-0.1%S). E, phosphorousternary eutectic. Etched with 4% nital, 100X

Spheroidal graphite cast iron, Fe-3.2C-2.5Si-0.05Mg wt%, contains graphite nodules in a matrix which is pearlitic. One of the nodules is surrounded by ferrite, simply because the region around the nodule is decarburized as carbon deposits on to the graphite. Etchant: Nital 2%.

IRON CARBON DIGRAM

IRON CARBON PHASE DIGRAM

The best way to understand the metallurgy is to examine the iron-carbon binary phase diagram. From the figure above we can make out the phases present in the material taken for analysis which is cementite, pearlite and transformed leduberite at 3% carbon.

[13]EXPERIMENTAL STUDY ON GRAY CAST IRON

COMPOSITION

MICROSTRUCTURE OBTAINED (G30),100X

MICROSTRUCTURE OBTAINED (G30) 400X

[14]INFERENCEAs it is seen from the various microstructures the graphite is present in the form of flakes which has precipitates from the austenitic phase. Also it is surrounded by the ferritic phase. All this is present in a matrix of pearlite as seen in the microstructure. Presence of certain inclusions can also be seen. From the experimental analysis it was seen that G-30 has finer flakes than G-25. This is due to the variation of chromium% in the two materials. Hence variation in percentage of chromium makes the graphite flakes finer.

[15] CONCLUSION

Modern polishing materials and procedures can be employed very effectively to reveal the microstructure of cast iron specimens. Graphite retention, always a problem with these metals, can be accomplished with a minimum

of difficulty. Crossed polarized light is very useful for observing graphite substructure. Etching brings out the matrix constituents.

Selective etching with color producing films, briefly discussed here, is a highly informative tool. This will be discussed in more detail in a future issue.

[1]I learnt the procedure to prepare the specimen for microstructure analysis.

[2] Extreme literature survey of various microstructure helped us to understand the Microstructure of our materials.[3] With the literature survey we can explain the respective microstructure.

[16]16SCOPE[1]To observe the microstructure under high magnification microscopes.[2] To observe the microstructure under different heat treatment condition.[3] It is interesting to observe the microstructures under SEM (Scanning electron microscope) & Perform ERAX at various places.

[17]METHODOLOGY:· Grey cast iron, aluminum and brass have been selected to observe the various micro constituent Present.· The raw materials are cut to get the required dimensions using abrasive cutting machine.· The materials are subjected to polishing and etching with the help of belt grinder, polishing Machine/electro polisher.· Using optical microscope the microstructure photographs are generated.· Correlation between various micro-constituents of the microstructure with mechanicalProperties will be studied.[18]TOOLS AND TECHNIQUES TO BE USED:Pneumatic Mounting Press· Metallography Abrasive Cutting Machine· General Purpose Belt Grinder· Metallography Polishing Machine· Micro hardness Tester (10gms to 2000gms)· Optical Microscope (2000X)

[19] REFERENCES:-

1] S. V. Kartoškin, Ju. P. Kremnev, L. Ja. Kozlov, Proceedings, 5thCongress of the Russian Founders. Radica publishers, Moscow,2001, p. 242-244.

2] L. Haenny, G.Zambelli, Engineering Fracture Mechanics 19 (1988) 1, 113 – 121

3] A. M. Bodiako, E. I. Marukovich, E. B. Ten, Choi Kiyoung, Proceedings, 65th World Foundry Congress. Gyeongju, Korea, 2002, p. 157 - 166.

4] http://www.man.lodz.pl/LISTY/ODLEW-PL/2007/02/att-0000/vol92.pdf

5]http://www.asminternational.org/portal/site/www/AsmStore/ProductDetails/?vgnextoid=2c97002b621b1210VgnVCM100000621e010aRCRD

6]http://www.sae.org/events/bce/tutorial-ihm.pdf

7]http://www.esigroup.com/products/casting/publications/Articles_PDF/MODELING%20MICROSTRUCTURE,%20MECHANICAL%20PROPERTIES%20AND%20DENSITY%20VARIATION%20OF%20CAST%20IRON.pdf

8] http://pwatlas.mt.umist.ac.uk/internetmicroscope/micrographs/microstructures/cast-iron.html

9]http://www.google.co.in/search?q=microstructure+of+cast+iron&hl=en&biw=1366&bih=677&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=u42qTdWSIMizrAehrIWoCA&ved=0CBkQsAQ

10]http://www.ductile.org/didata/Section3/3part2.htm#Impact%20Properties%20Effect%20of%20Microstructure