MATERIAL SCIENCE LECTURE NOTES.pptx

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1. MATERIAL SCIENCE BY- SAMEER VISHWAKARMA BHUPENDRA KUMAR SARASWAT UNIVERSITY POLYTECHNIC

2. SYLLABUS MODULE 1 Introduction: Material, History of Material Origin, Scope of Material Science, Overview of different engineering materials and applications , Classification of materials , Thermal, Chemical, Electrical, Mechanical properties of various materials, Present and future needs of materials , Overview of Biomaterials and semi conducting materials, Various issues of Material Usage- Economical, Environment and Social. Crystallography Fundamentals: Crystal, Unit Cell, Space Lattice, Arrangement of atoms in Simple Cubic Crystals, BCC, FCC and HCP Crystals, Number of atoms per unit Cell, Atomic Packing Factor. Metals And Alloys Introduction: History and development of iron and steel, Different iron ores, Raw Materials in Production of Iron and Steel, Basic Process of iron-making and steel-making, Classification of iron and steel, Cast Iron: Different types of Cast Iron, manufacture and their usage.

3. SYLLABUS MODULE 2 Steels Steels and alloy steel, Classification of plain carbon steels, Availability, Properties and usage of different types of Plain Carbon Steels, Effect of various alloys on properties of steel, Uses of alloy steels (high speed steel, stainless steel, spring steel, silicon steel) Spring materials, Iron –carbon diagram, TTT Diagram. Concepts and effects of Heat Treatment Purpose of heat treatment, Cooling Curves various heaT treatment processes hardening, tempering, nnealing, normalizing, Case hardening and surface hardening. Non Ferrous Materials: Properties and uses of Light Metals and their alloys, properties and uses of White Metals and their alloys. Engineering Plastics Important sources of plastics, Classification-thermoplastic and thermo set and their uses, Various Trade names of engg. Plastics, Plastic Coatings Ceramics: Classification, properties, applications Heat insulating materials Miscellaneous Materials Properties and uses of Asbestos, Glass wool, thermocole, cork, mica. Overview of tool and die materials, Materials for bearing metals, Materials for Nuclear Energy, Refractory materials. Composites Classification, properties, applications

4. WHY TO STUDY MATERIAL SCIENCE To understand how materials are made To know how materials behave under load and on environmental conditions To know the effect of mixing and how mixing (alloying) changes the material properties To know about structure of material To select a material for different engineering vapplications To optimize the overall cost of a product For research To become multidisiplinary engineer

5. MODULE - 1

6. CHAPTER 1 HISTORY, CLASSIFICATION AND PROPERTIES OF MATERIALS https://www.youtube.com/watch?v=qShgQd6aAEc&t=409s

7. History of Material Origin TIME DURATION EXAMPLES PRE-HISTORY 300,000 BCE FLINT STONE AGE 30,000 BCE–10,000 BCE STONE AXE BRONZE AGE  5,500 BCE-3000 BCE GOLD, SILVER, COPPER , COOPER –TIN ALLOYS IRON AGE 1,200 BCE- 2 ND CENTURY IRON, GLASS, STEELS , PAPER ROMAN AGE (ANTIQUITY) 31 BC – 5 TH CENTURY CEMENT, WOOD, BONE, STONES, CRYSTALLINE MATERIALS, ASBESTOS, CORK, OXIDES MIDDLE AGE A.D. 476 -A.D. 1450 DEMASCUS STEEL, LEATHER, LINEN, SILK, FUR, STEEL UTENSILS EARLY MODERN PERIOD A.D. 1450-A.D. 1750 RUBBER, MICROSCOPE, TELESCOPE, ZINC, P.O.P., ZINC-ACID BATTERY, ALUMINUM MODERN AGE A.D. 1750-Present ALLOYS, CERAMICS, SILICON CHIPS, POLYMERS,

8. ENGINEERING MATERIALS Engineering materials  refers to the group of materials that are used in the construction of manmade structures and components. The primary function of an engineering material is to withstand applied loading without breaking and without exhibiting excessive deflection.

9. CLASSIFICATION OF MATERIALS

10. PROPERTIES OF MATERIALS PHYSICAL PROPERTIES CHEMICAL PROPERTIES MECHANICAL PROPERTIES ELECTRICAL PROPERTIES THERMAL PROPETIES https://www.youtube.com/watch?v=B15xoj3b4eo https://www.youtube.com/watch?v=E5uc4Brkivc&t=1643s

11. PHYSICAL PROPERTIES OF MATERIAL https://www.youtube.com/watch?v=B15xoj3b4eo The physical properties of a material are those which can be observed without any change of the identity of material. Density Specific gravity State Change temperatures Coefficients of thermal expansion Specific Heat Latent heat Fluidity Weld ability Elasticity Plasticity Porosity Thermal conductivity Electrical Conductivity

12. CHEMICAL PROPERTIES OF MATERIAL https://www.youtube.com/watch?v=B15xoj3b4eo Chemical composition Atomic bonding Corrosion resistance Acidity or Alkalinity

13. MECHANICAL PROPERTIES OF MATERIAL Strength Elasticity Plasticity Hardness Toughness Brittleness Stiffness Ductility Malleability Cohesion Impact strength Fatigue Creep https://www.youtube.com/watch?v=E5uc4Brkivc&t=1643s

14. STRENGTH Strength is the mechanical property that enables a metal to resist deformation load. The strength of a material is its capacity to withstand destruction under the action of external loads . The stronger the materials the greater the load it can withstand.

15. ELASTICITY According to dictionary elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed. When a material has a load applied to it, the load causes the material to deform. The elasticity of a material is its power of coming back to its original position after deformation when the stress or load is released. Heat-treated springs, rubber etc are good examples of elastic materials.

16. PLASTICITY The plasticity of a material is its ability to undergo some permanent deformation without rupture(brittle). Plastic deformation will take place only after the elastic range has been exceeded. Pieces of evidence of plastic action in structural materials are called yield, plastic flow and creep. Materials such as clay, lead etc are plastic at room temperature, and steel plastic when at bright red-heat.  

17. HARDNESS The resistance of a material to force penetration or bending is hardness . The hardness is the ability of a material to resist scratching, abrasion, cutting or penetration. Hardness indicates the degree of hardness of a material that can be imparted particularly steel by the process of hardening. It determines the depth and distribution of hardness is introduce by the quenching process.

18. TOUGHNESS It is the property of a material which enables it to withstand shock or impact. Toughness is the opposite condition of brittleness. The toughness is may be considering the combination of strength and plasticity. Manganese steel, wrought iron, mild steel etc are examples of toughness materials.

19. BRITTLENESS The brittleness of a property of a material which enables it to withstand permanent deformation. Cast iron, glass are examples of brittle materials. They will break rather than bend under shock or impact. Generally, the brittle metals have high compressive strength but low in tensile strength.

20. STIFFNESS It is a mechanical property. The stiffness is the resistance of a material to elastic deformation or deflection. In stiffness, a material which suffers light deformation under load has a high degree of stiffness. The stiffness of a structure is important in many engineering applications, so the modulus of elasticity is often one of the primary properties when selecting a material.

21. DUCTILITY The ductility is a property of a material which enables it to be drawn out into a thin wire. Mild steel, copper, aluminium are the good examples of a ductile material.

22. MALLEABILITY The malleability is a property of a material which permits it to be hammered or rolled into sheets of other sizes and shapes. Aluminium, copper, tin, lead etc are examples of malleable metals.

23. COHESION It is a mechanical property. The cohesion is a property of a solid body by virtue of which they resist from being broken into a fragment.

24. IMPACT STRENGTH The impact strength is the ability of a metal to resist suddenly applied loads.

25. FATIGUE The fatigue is the long effect of repeated straining action which causes the strain or break of the material. It is the term 'fatigue' use to describe the fatigue of material under repeatedly applied forces.

26. CREEP The creep is a slow and progressive deformation of a material with time at a constant force. The simplest type of creep deformation is viscous flow. Some metals are generally exhibiting creep at high temperature, whereas plastic, rubber, and similar amorphous material are very temperature sensitive to creep. The force for a specified rate of strain at constant temperature is called creep strength.

27. ELECTRICAL PROPERTIES OF MATERIAL Resistivity Conductivity Permittivity Thermoelectricity

28. THERMAL PROPERTIES OF MATERIAL Specific Heat Heat capacity Thermal Expansion Thermal conductivity Melting point Boiling point Freezing point Dew point

29. Specific Heat  the quantity of heat required to raise the temperature of one gram of a substance by one Celsius degree. Heat capacity the amount of heat required to raise the temperature of an object by 1 degree Celcius. Thermal Expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature. Thermal conductivity The rate at which heat is transferred by conduction through a unit cross-section area of a material.

30. Melting point The temperature at which it changes state from solid to liquid. Boiling point The temperature at which the liquid boils and changes into gaseous state at the atmospheric pressure is called boiling point. Freezing point Liquids have a characteristic temperature at which they turn into solids, known as their freezing point. Dew point The temperature at which the air is completely saturated and can't hold any more moisture.

31. BIOMATERIALS Polymers, synthetic and natural Metals Ceramics Composites

32. CHAPTER 2 BIOMATERIALS

33. CHAPTER 3 CONDUCTOR, SEMICONDUCTOR AND INSULATORS

34. Conductor, semi conductors and insulators Insulators An insulator is a material that does not conduct electrical current under normal conditions. Most good insulators are compounds rather than single-element materials and have very high resistivities. Valence electrons are tightly bound to the atoms; therefore, there are very few free electrons in an insulator. Examples of insulators are rubber, plastics, glass, and quartz. Conductors A conductor is a material that easily conducts electrical current. Most metals are good conductors. The best conductors are single-element materials, such as copper (Cu), silver (Ag), gold (Au), and aluminum (Al), which are characterized by atoms with only one valence electron very loosely bound to the atom. These loosely bound valence electrons become free electrons. Therefore, in a conductive material the free electrons are valence electrons.

35. Conductor, semi conductors and insulators Semiconductors A semiconductor is a material that is between conductors and insulators in its ability to conduct electrical current. A semiconductor in its pure (intrinsic) state is neither a good conductor nor a good insulator. Single element semiconductors are antimony (Sb), arsenic (As), boron (B), silicon (Si), and germanium (Ge). Compound semiconductors such as gallium arsenide, are also commonly used. The single-element semiconductors are characterized by atoms with four valence electrons. Silicon is the most commonly used semiconductor.

36. Insulators, Conductors, Semiconductors from energy band structures E valence band filled conduction band empty Forbidden region E g > 5eV Band gap E conduction band E g < 5eV Band gap + - electron hole E valence band partially-filled band Insulator Semiconductor Conductor

37. CHAPTER 4 CRYTALLOGRAPHY https://www.youtube.com/watch?v=zuR2wnJlrOk&t=998s

38. CRYSTALLOGRAPHY CRYSTAL: A crystal is a solid whose atoms are arranged in a "highly ordered" repeating pattern. These patterns are called crystal systems. If a mineral has its atoms arranged in one of them, then that mineral is a crystal. UNIT CELL : A unit cell is the smallest representation of an entire crystal. The unit cell is the simplest repeating unit in the crystal. Opposite faces of a unit cell are parallel. SPACE LATTICE : A space lattice is an array of points showing how particles (atoms, ions or molecules) are arranged at different sites in three dimensional spaces.

39. SIMPLE CUBIC CELL The simple cubic unit cell is delineated by eight atoms, which mark the actual cube. These are corner atoms, so each one only contributes one eighth of an atom to the unit cell, thus giving us only one net atom.

40. BODY CENTRED CUBIC (BCC) CELL A BCC unit cell has atoms at each corner of the cube and an atom at the centre of the structure. The diagram shown below is an open structure. According to this structure, the atom at the body centre wholly belongs to the unit cell in which it is present. In BCC unit cell every corner has atoms. There is one atom present at the centre of the structure Below diagram is an open structure According to this structure atom at the body centres wholly belongs to the unit cell in which it is present.

41. FACE CENTRED CUBIC (fcc) CELL An FCC unit cell contains atoms at all the corners of the crystal lattice and at the centre of all the faces of the cube. The atom present at the face-centered is shared between 2 adjacent unit cells and only 1/2 of each atom belongs to an individual cell. In FCC unit cell atoms are present in all the corners of the crystal lattice Also, there is an atom present at the centre of every face of the cube This face-centre atom is shared between two adjacent unit cells Only 12 of each atom belongs to a unit cell

42. HEXAGONAL CLOSE PACKED (HCP) CELL The Hexagonal Close-Packed (HCP) crystal structure is one of the most common ways for atoms to arrange themselves in metals.  HCP is one of the most stable crystal structures and has the highest packing density.

43. ATOMIC PACKING FACTOR (APF) Atomic packing is the ratio of total volume of atoms and total volume of the unit cell. APF = APF = Where Ne = Effective number of atoms = Ni + (Nf /2) + (Nc / No of corners) here, Ni = Number of atoms inside the cell Nf = Number of atoms on the face Nc = Number of corners

44. Apf for Simple Cubic Cell

45. Apf for BCC

46. Apf for fcc

47. CHAPTER 5 INTRODUCTION TO IRON AND STEEL

48. IRON ORES HEMATITE MAGNETITE SIDERITE LIMONITE

49. Making Pig Iron (Blast Furnace) Go throu the video: https://www.youtube.com/shorts/18dVw06bJ0g Making Cast Iron (Cupola Furnace) Go throu the video: https://www.youtube.com/watch?v=znL8sqK1-sQ

50. Types of Caste Iron There are primarily 4 different types of cast iron. Different processing techniques can be used to produce the desired type, which include: Grey Cast Iron White Cast Iron Ductile Cast Iron Malleable Cast Iron

51. Grey Cast Iron Grey Cast iron refers to a type of cast iron that has been processed to produce free graphite (carbon) molecules in the metal. The size and structure of the graphite can be controlled by moderating the cooling rate of the iron and by adding silicon to stabilize the graphite. When Grey Cast Iron fractures, it fractures along the graphite flakes and has a grey appearance at the fracture site. Grey Cast Iron is not as ductile as other cast irons, however it has an excellent thermal conductivity and the best damping capacity of all cast irons. It is also hard wearing making it a popular material to work with. The high wear resistance, high thermal conductivity, and the excellent damping capacity of Grey Cast Iron makes it ideal for engine blocks, fly wheels, manifolds, and cookware. It has Good machinability It has Good resistance to galling and wear It has high compressive strength It is brittle

52. White Cast Iron White Cast Iron is named based on the appearance of fractures. By tightly controlling the carbon content, reducing the silicon content, and controlling the cooling rate of iron, it is possible to consume all carbon in the iron in the generation of iron carbide. This ensures there are no free graphite molecules and creates an iron that is hard, brittle, extremely wear resistant and has a high compressive strength. As there are no free graphite molecules, any fracture site appears white, giving White Cast Iron its name. White Cast Iron is used primarily for its wear resistant properties in pump housings, mill linings and rods, crushers and brake shoes. It has High compressive strength It is difficult to machine It has Good hardness It has Resistance to wear

53. Ductile Cast Iron Ductile Cast Iron is produced by adding a small amount of magnesium, approximately 0.2%, which makes the graphite form spherical inclusions that give a more ductile cast iron. It can also withstand thermal cycling better than other cast iron products. Ductile Cast Iron is predominantly used for its relative ductility and can be found extensively in water and sewerage infrastructure. The thermal cycling resistance also makes it a popular choice for crankshafts, gears, heavy duty suspensions and brakes. It has High ductility It has High strength

54. Malleable Cast Iron Malleable Cast Iron is a type of cast iron that is manufactured by heat treating White Cast Iron to break down the iron carbide back into free graphite. This produces a malleable and ductile product that has good fracture toughness at low temperatures. Malleable Cast Iron is used for electrical fittings, mining equipment and machine parts. Its properties are They have High ductility They are tougher than gray cast iron They can be twisted or bent without fracture They have excellent machining capabilities

55. Advantages of cast iron It has Good casting properties It is available in large quantities, hence produced in mass scale. Tools required for casting process are relatively cheap and inexpensive. This results into low cost of its products. It can be given any complex shape and size without using costly machining operations It has three to five times more compression strength compared to steel It has Good machinability (gray cast iron) It has excellent anti-vibration (or damping) properties hence it is used to make machine frames It has good Sensibility It has excellent resistance to wear It has constant Mechanical properties between 20 to 350 degree Celsius It has very low notch sensitivity It has Low stress concentration It bears Low cost It has Durability It has Resistance to deformation

56. Disadvantages of cast iron It is Prone to rusting It has poor tensile strength Its parts are section sensitive, this is due to slow cooling of thick sections. failure of Its parts is sudden and total, it does not exhibit yield point. It has poor impact resistance Compared to steel it has poor machinability It has High weight to strength ratio It has High brittleness It is Non machinable (white cast iron)

57. Applications of Cast Iron It is used in making pipes, to carry suitable fluids It is used in making different machines It is used in making automotive parts It is used in making pots pans and utensils It is used in making anchor for ships.

58. MODULE - 2

59. CHAPTER 1 TYPES OF STEEL EFFECT OF VARIOUS ELEMENTS ON STEEL APPLICATIONS OF STEEL

60. Tantalum (TA) Used as stabilizing elements in stainless steels. Each has a high affinity for carbon and forms carbides, which are uniformly dispersed throughout the steel. Thus, localized precipitation of carbides at grain boundaries is prevented. Titanium (TI) Used as stabilizing elements in stainless steels. Each has a high affinity for carbon and forms carbides, which are uniformly dispersed throughout the steel. Thus, localized precipitation of carbides at grain boundaries is prevented. Tungsten (W) Increases strength, wear resistance, hardness and toughness. Tungsten steels have superior hot-working and greater cutting efficiency at elevated temperatures. Vanadium (V) Increases strength, hardness, wear resistance and resistance to shock impact. It retards grain growth, permitting higher quenching temperatures. It also enhances the red-hardness properties of high-speed metal cutting tools.

61. TYPES OF STEEL 1. CARBON STEEL Carbon steel looks dull, matte-like, and is known to be vulnerable to corrosion. Overall, there are three subtypes to this one: low, medium, and high carbon steel, with low containing about .30% of carbon, medium .60%, and high 1.5%. The name itself actually comes from the reality that they contain a very small amount of other alloying elements. They are exceptionally strong, which is why they are often used to make things like knives, high-tension wires, automotive parts, and other similar items.

62. 2. ALLOY STEEL Next up is alloy steel, which is a mixture of several different metals, like nickel, copper, and aluminum. These tend to be more on the cheaper side, more resistant to corrosion and are favored for some car parts, pipelines, ship hulls, and mechanical projects. For this one, the strength depends on the concentration of the elements that it contains.

63. 3. TOOL STEEL Tool steel is famous for being hard and both heat and scrape resistant. The name is derived from the fact that they are very commonly used to make metal tools, like hammers For these, they are made up of things like cobalt, molybdenum, and tungsten, and that is the underlying reason why tool steel has such advanced durability and heat resistance features.

64. 4. STAINLESS STEEL Last but not least, stainless steels are probably the most well-known type on the market. This type is shiny and generally has around 10 to 20% chromium, which is their main alloying element. With this combination, it allows the steel to be resistant to corrosion and very easily molded into varying shapes. Because of their easy manipulation, flexibility, and quality, stainless steel can be found in surgical equipment, home applications, silverware, and even implemented as exterior cladding for commercial/industrial buildings.

65. EFFECTS OF COMMON ALLOYING ELEMENTS IN STEEL Carbon (C) The most important constituent of steel. It raises tensile strength, hardness, and resistance to wear and abrasion. It lowers ductility, toughness and machinability. Chromium (CR) Increases tensile strength, hardness, hardenability, toughness, resistance to wear and abrasion, resistance to corrosion, and scaling at elevated temperatures. Cobalt (CO) Increases strength and hardness and permits higher quenching temperatures and increases the red hardness of high speed steel. It also intensifies the individual effects of other major elements in more complex steels. Columbium (CB) Used as stabilizing elements in stainless steels. Each has a high affinity for carbon and forms carbides, which are uniformly dispersed throughout the steel. Thus, localized precipitation of carbides at grain boundaries is prevented.

66. Copper (CU) In significant amounts is detrimental to hot-working steels. Copper negatively affects forge welding, but does not seriously affect arc or oxyacetylene welding. Copper can be detrimental to surface quality. Copper is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20%. Weathering steels are sold having greater than 0.20% Copper. Manganese (MN) A deoxidizer and degasifier and reacts with sulfur to improve forgeability. It increases tensile strength, hardness, hardenability and resistance to wear. It decreases tendency toward scaling and distortion. It increases the rate of carbon-penetration in carburizing. Molybdenum (MO) Increases strength, hardness, hardenability, and toughness, as well as creep resistance and strength at elevated temperatures. It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements. In hot-work steels and high speed steels, it increases red-hardness properties.

67. Phosphorus (P) Increases strength and hardness and improves machinability. However, it adds marked brittleness or cold-shortness to steel. Silicon (SI) A deoxidizer and degasifier. It increases tensile and yield strength, hardness, forgeability and magnetic permeability. Sulfur (S) Improves machinability in free-cutting steels, but without sufficient manganese it produces brittleness at red heat. It decreases weldability, impact toughness and ductility. Nickel (NI) Increases strength and hardness without sacrificing ductility and toughness. It also increases resistance to corrosion and scaling at elevated temperatures when introduced in suitable quantities in high-chromium (stainless) steels.

68. APPLICATIONS OF STEEL Long A steel bridge A steel pylon suspending overhead power lines As reinforcing bars and mesh in reinforced concrete Railroad tracks Structural steel in modern buildings and bridges Wires Input to reforging applications

69. APPLICATIONS OF STEEL Flat carbon Major appliances Magnetic cores The inside and outside body of automobiles, trains, and ships. Weathering (COR-TEN) Intermodal containers Outdoor sculptures Architecture Highliner train cars

70. APPLICATIONS OF STEEL Stainless Steel A stainless steel gravy boat Cutlery Rulers Surgical instruments Watches Guns Rail passenger vehicles Tablets Trash Cans Body piercing jewellery Inexpensive rings Components of spacecraft and space stations

71. CHAPTER 2 IRON-CARBON DIAGRAM TTT DIAGRAM HEAT TREATMENT REFER- https://www.youtube.com/watch?v=4F6ANK6fIUA

72. Iron Carbon Phase Diagram

73. Allotropic Transformations in Iron Iron is an allotropic metal, which means that it can exist in more than one type of lattice structure depending upon temperature. A cooling curve for pure iron is shown in fig:

74. The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram The Fe-C (or more precisely the Fe-Fe3C) diagram is an important one. Cementite is a metastable phase and ‘strictly speaking’ should not be included in a phase diagram. But the decomposition rate of cementite is small and hence can be thought of as ‘stable enough’ to be included in a phase diagram. Hence, we typically consider the Fe-Fe3C part of the Fe-C phase diagram. C is an interstitial impurity in Fe. It forms a solid solution with α, γ, δ phases of iron

75. In their simplest form, steels are alloys of Iron (Fe) and Carbon (C). The Fe-C phase diagram is a fairly complex one, but we will only consider the steel part of the diagram, up to around 7% Carbon. Carbon Solubility in Iron Solubility of carbon in Fe is function of structure and temperature.

76. Phases appeared in Fe–Fe3C Phase Diagram 1. α -ferrite ( solid solution of C in BCC Fe) It is an interstitial solid solution of a small amount of carbon dissolved in α iron. BCC has relatively small interstitial positions The maximum solubility is 0.022%C at 723 ° C and it dissolves only 0.008%C at room temperature . BCC has relatively small interstitial positions It is the softest structure that appears on the diagram • Transforms to FCC γ-austenite at 912 °C

77. 2. γ -austenite –(solid solution of C in FCC Fe) • The maximum solubility of C is 2.14 wt %. at 1147 ° C . FCC has larger interstitial positions. • Transforms to BCC δ-ferrite at 1395 °C • Is not stable below the eutectic temperature(727°C) unless cooled rapidly (discuss later in unit4)

78. solid solution of carbon in α-iron. α-ferrite BCC crystal structure low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT γ ( Austenite) Interstitial solid solution of carbon in γ iron. Austenite has FCC crystal structure, high solubility of carbon up to 2.14% at (1147ºC). Soft, ductile, malleable and non-magnetic γ

79. 3. δ -ferrite (solid solution of C in BCC Fe) • The same structure as α-ferrite • Stable only at high T, above 1394 °C . The stability of the phase ranges between 1394-1539°C. Melts at 1538 °C 4. Fe-C liquid solution

80. solid solution of carbon in α-iron. α-ferrite BCC crystal structure low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT δ -( FERRRITE) Solid solution of carbon in δ-iron. The crystal structure of δ-ferrite is BCC (cubic body centered). δ

81. 5. Fe3C (iron carbide or cementite) • This intermetallic compound is metastable, it remains as a compound indefinitely at room T, but decomposes (very slowly, within several years) into α-Fe and C (graphite) at 650 - 700 °C It is typically hard and brittle interstitial compound of low tensile strength (approx. 5000psi) but high compressive strength. It is the hardest structure that appears on the diagram.

82. solid solution of carbon in α-iron. α-ferrite BCC crystal structure low solubility of carbon – up to 0.25% at 1333 ºF (723ºC). α-ferrite exists at RT Fe 3 C-( Cementite) Intermetallic compound, having fixed composition Fe 3 C. Orthorhombic crystal structure,12-iron .4- carbon Hard and brittle Ferromagnetic upto 210 C Fe 3 C

83. Peritectic Reaction: L + δ → γ (0.55%C) (0.10%C) (0.18%C) S1 + L S2 δ = 0.55 0.55-0.18 0.55-0.1 X 100 = 82.2 % 0.18-0.1 0.55-0.1 L = X 100 = 17.8% 1492 ºC

84. Eutectic and eutectoid reactions in Fe–Fe3C γ (0.76 wt % C) ↔ α (0.022 wt % C) + Fe3C

85. Eutectoid Reaction: γ → α + Fe 3 C S1 S2 + S3 727 ºC α = 6.67-0.8 6.67-0.008 x 100 = 88.1% Fe 3 C = 0.8- 0.025 6.67-0.008 100 x = 11.09 % (0.80% C) (0.025% C) (6.67%C) Fe 3 C Fe 3 C Pearlite

86. Eutectic Reaction (at) Liquid → γ + Fe3C (4.30%C) (2.00% C) (6.67%C) L1 S1 + S2 Ledeburite 1147 ºC

87. TTT diagrams TTT diagram stands for “time-temperature-transformation” diagram. It is also called isothermal transformation diagram Definition: TTT diagrams give the kinetics of isothermal transformations.

88. T (Time) T(Temperature) T(Transformation) diagram is a plot of temperature versus the logarithm of time for a steel alloy of definite composition. It is used to determine when transformations begin and end for an isothermal (constant temperature) heat treatment of a previously austenitized alloy. When austenite is cooled slowly to a temperature below LCT (Lower Critical Temperature), the structure that is formed is Pearlite . As the cooling rate increases, the pearlite transformation temperature gets lower. The microstructure of the material is significantly altered as the cooling rate increases. By heating and cooling a series of samples, the history of the austenite transformation may be recorded. TTT diagram indicates when a specific transformation starts and ends and it also shows what percentage of transformation of austenite at a particular temperature is achieved. TTT DIAGRAM

89. TTT DIAGRAM

90. Stable Austenite Unstable Austenite Transformation starts/begins Transformation ends Coarse Pearlite Fine Pearlite Unstable Austenite Feathery Bainite Acicular Bainite M s M f Austenite + Martensite Martensite Time-Temperature Transformation Curves

91. STABLE AUSTENITE Bianite in feather shaped patches Degree of under cooling high Sluggish transformation Austenite to Coarse Pearlite Greater time for diffusion Slow rate of diffusion of Carbon atoms retards increased tendency of Austenite transformation , 550 550-220 Near A 1

92. AUSTENITE PEARLITE

93. Austenite is stable at temperatures above LCT but unstable below LCT. Left curve indicates the start of a transformation and right curve represents the finish of a transformation. The area between the two curves indicates the transformation of austenite to different types of crystal structures. (Austenite to pearlite , austenite to martensite , austenite to bainite transformation.) Isothermal Transform Diagram shows that γ to transformation (a) is rapid! at speed of sound; (b) the percentage of transformation depends on Temperature only:

94. Upper half of TTT Diagram (Austenite- Pearlite Transformation Area)

95. As indicated when is cooled to temperatures below LCT, it transforms to other crystal structures due to its unstable nature. A specific cooling rate may be chosen so that the transformation of austenite can be 50 %, 100 % etc. If the cooling rate is very slow such as annealing process, the cooling curve passes through the entire transformation area and the end product of this the cooling process becomes 100% Pearlite . In other words, when slow cooling is applied, all the Austenite will transform to Pearlite . If the cooling curve passes through the middle of the transformation area, the end product is 50 % Austenite and 50 % Pearlite , which means that at certain cooling rates we can retain part of the Austenite, without transforming it into Pearlite .

96. Lower half of TTT Diagram (Austenite- Martensite and Bainite Transformation Areas)

97. If a cooling rate is very high, the cooling curve will remain on the left hand side of the Transformation Start curve. In this case all Austenite will transform to Martensite . If there is no interruption in cooling the end product will be martensite .

98. TTT diagram gives - Nature of transformation-isothermal or athermal (time independent) or mixed - Type of transformation-reconstructive, or displacive - Rate of transformation - Stability of phases under isothermal transformation conditions - Temperature or time required to start or finish transformation - Qualitative information about size scale of product - Hardness of transformed products

99. Factors affecting TTT diagram Composition of steel- (a) carbon wt%, (b) alloying element wt% Grain size of austenite Heterogeneity of austenite

100. HEAT TREATMENT Heat treatment is a method used to alter the physical, and sometimes chemical properties of a material. The most common application is metallurgical  It involves the use of heating or chilling, normally to extreme temperatures, to achieve a desired result such as hardening or softening of a material It applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally Generally, heat treatment uses phase transformation during heating and cooling to change a microstructure in a solid state.

101. Hardening : When a metal is hardened, it’s heated to a point where the elements in the material transform into a solution. Defects in the structure are then transformed by creating a reliable solution and strengthening the metal. This increases the hardness of the metal or alloy, making it less malleable.    Annealing : This process is used on metals like copper, aluminum, silver, steel, and brass. These materials are heated to a certain temperature, are held at that temperature until transformation occurs, and then are slowly air-dried.  This process softens the metal, making it more workable and less likely to fracture or crack.  HEAT TREATMENT : TYPES

102. Tempering : Some materials like iron-based alloys are very hard, making them brittle. Tempering can reduce brittleness and strengthen the metal. In the tempering process, the metal is heated to a temperature lower than the critical point to reduce brittleness and maintain hardness.  Case Hardening : The outside of the material is hardened while the inside remains soft. Since hardening can cause materials to become brittle, case hardening is used for materials that require flexibility while maintaining a durable wear layer.  Normalization : Similar to annealing, this process makes the steel more tough and ductile by heating the material to critical temperatures and keeping it at this temperature until transformation occurs. 

103. CHAPTER 3 NON-FERROUS METALS Aluminium and its alloys Copper and its alloys Tin and its alloys Zinc and its alloys

104. ALUMINIUM