Chemistry For Engineers: Lesson 4 - Engineering Materials (Metals) PDF

LESSON 4 THE CHEMISTRY OF ENGINEERING MATERIALS (METALS) METALS INTRODUCTION ◼ employed for various engineering purposes and requirements ◼ iron is the most popular metal in the field of engineering ◼ ALL the metals have a crystalline structure ALLOY ◼ An alloy is a mixture or compou...

LESSON 4 THE CHEMISTRY OF ENGINEERING MATERIALS (METALS) METALS INTRODUCTION ◼ employed for various engineering purposes and requirements ◼ iron is the most popular metal in the field of engineering ◼ ALL the metals have a crystalline structure ALLOY ◼ An alloy is a mixture or compound of two or more elements, at least one of which is metallic ◼ Alloying enhances some properties, as required by engineering applications, such as strength and hardness in comparison to pure metals ◼ Classified into solid solution and intermediate phase ALLOY ◼ Solid solution is an alloy in which one element is dissolved in another to form a single-phase structure ◼ In a solid solution, the solvent or base element is metallic, and the dissolved element can be either metallic or nonmetal ◼ Solid solutions can be Substitutional Solid Solution or Interstitial Solid Solution ALLOY Substitutional solid solution - atoms of solvent element are replaced in its unit cell by dissolved element. Interstitial solid solution - atoms of dissolving element fit into vacant spaces between base metal atoms Substitutional solid solution (left) and Interstitial in the lattice structure. solid solution (right) ALLOY ◼ Intermediate phases - There are usually limits to the solubility of one element in another. When the amount of the dissolving element in the alloy exceeds the solid solubility limit of the base metal, a second phase forms in the alloy. The term intermediate phase is used to describe it because its chemical composition is intermediate between the two pure elements. Its crystalline structure is also different from those of the pure metals. IMPORTANCE OF METALS ◼ High stiffness and strength – can be alloyed for high rigidity, strength, and hardness ◼ Toughness – capacity to absorb energy better than other classes of materials ◼ Good electrical conductivity – metals are conductors ◼ Good thermal conductivity – conduct heat better than ceramics or polymers ◼ Cost – the price of steel is very competitive with other engineering materials METALS USED IN MANUFACTURING PROCESS ◼ Cast Metal - starting form is a casting ◼ Wrought Metal - the metal has been worked or can be worked after casting ◼ Powdered Metal - starting form is very small powders for conversion into parts using powder metallurgy techniques CLASSIFICATION OF METALS FERROUS METALS ◼ These metals contain iron as main constituent ◼ Ferrous metals are classified as cast iron, wrought iron, and steel depending upon ingredients and percentage of carbon content NON-FERROUS METALS ◼ These metals practically do not contain iron FERROUS METALS Cast Iron (C.I.) Cast Iron contains a higher percentage of carbon ranging from 2 to 4.23 Cast iron is manufactured by melting of pig iron with coke and lime stone. The furnace used is known as CUPOLA. Properties of Cast Iron 1. It can be hardened by heating and sudden cooling, but it cannot be tempered. 2. It does not rust easily. 3. It is fusible. 4. It is hard and at the same time brittle. FERROUS METALS Cast Iron (C.I.) Classification 1. Grey Cast Iron - The carbon content is about 3% ad when fractured gives a grey appearance. It is soft and readily melts. Its strength is weak and is used for casting cylinders, pistons, manholes etc. 2. White Cast Iron - Its carbon content is 2.0 to 2.5%. It contains carbon in chemical form and on fracturing gives silver white luster. It is hard, not workable on machines and is used for preparing pump liners, drawing dies etc., FERROUS METALS Cast Iron (C.I.) Classification 3. Chilled Cast Iron - Its carbon content is 3.3%. It is produced by casting the molten metal against a metal chiller to obtain a surface of white cast iron. This is hard to a certain depth from the outer surface, which indicates the white iron. The inner portion of the body is made up of grey iron which is soft. It is used for manufacturing rail car wheels, dies, sprockets etc. FERROUS METALS Cast Iron (C.I.) 4. Malleable Cast Iron - Its carbon content is 2.3%. The composition of this is so adjusted that it becomes malleable. It is done by extracting a portion of carbon from cast iron. It has high field strength and used for manufacture of automobile and railway equipment such as rail cars, crank shafts gear boxes etc. 5. Toughened Cast Iron - It is obtained by melting cast-iron with wrought iron scrap. The proportion of wrought-iron scrap is about 1/4 to 1/7th of cast-iron. FERROUS METALS ◼ FERROUS METALS Wrought Iron Properties 1. It is soft at white stage of heat. It can be easily forged and welded. 2. It is ductile, malleable and tough. 3. Its melting point is 1500°C. 4. It is resistant to corrosion. FERROUS METALS Steel Steel is defined as the iron alloy with a carbon content of up to 2.0%. Types of steel include low carbon steel or mild steel, medium carbon steel, and high carbon steel. FERROUS METALS Steel Carbon Content Properties Uses Low Carbon or Mild 0.10 to 0.3% ∙ It can be easily hardened and tempered Sheets, Tin Plates ∙ It is malleable and ductile ∙ It can be forged and welded ∙ It rusts easily ∙ Specific gravity is 7.8 Medium Carbon 0.3 to 0.6% These steels have high strength, toughness, Boiler plates, Railway hardness and stiffness tyres, pressing dies High Carbon 0.6 to 1.50% ∙ It can be easily hammered and tempered Springs, Hammers, Drills, ∙ It can be magnetize permanently Chisel ∙ It is granular in structure ∙ Specific gravity is 7.9 FERROUS METALS Alloy Steel Steel, to which elements other than carbon are added in sufficient quantity, in order to obtain special properties, is known as alloy steel. Examples of alloy steels include chromium steel, cobalt steel, manganese steel, tungsten steel, vanadium steel and Nickel steel. FERROUS METALS Alloy Steel Alloying elements added Properties Uses Chromium Steel Chromium up to 0.9%, Highly ductile, can be easily Used for locomotive springs, Vanadium up to 0.15% worked and welded pistons and bolts Cobalt Steel Cobalt is added to high Possesses magnetic properties Used for making permanent carbon steel magnet with strong magnetic field Manganese Steel Manganese up to 1.90% It is hard, strong and ductile. It Used for gears gives resistance to abrasion. Tungsten Steel or Tungsten content up to 7% It is hard and maintains cutting Used for lathe tools, drill High Speed Steel power at high temperature cutters Nickel Steel Nickel up to 3.5% It is hard and ductile Used for boiler plates, structural steel propeller shafts Vanadium Steel Vanadium content up to 0.2% Strong and ductile, elastic limit Used for automobile parts, is high, resists shocks springs NON-FERROUS METALS Aluminum ◼ It is a very light and useful non-ferrous metal. It Uses of Aluminum is produced mainly from bauxite which is 1. For manufacturing of electrical conductors. hydrated oxide of aluminum. 2. Making alloys. Properties of Aluminum 3. For manufacture of cooking utensils, surgical 1. a tin white metal. instruments, etc. 2. good conductor of heat and electricity. 4. For making parts of air crafts. 3. malleable, ductile and very light. 5. In manufacture of paints 4. highly electro positive element. NON-FERROUS METALS Copper Copper is one of the most useful non-ferrous Uses of Copper metals. It occurs in nature in a free state as well as 1. For the manufacture of electrical cables and combined state. wires and lightning conductors. Properties of Copper 2. For making alloys. 1. Bright shining metal of reddish color. 3. For house hold utensils. 2. high tensile strength. 4. For bolts and nuts. 3. very malleable and ductile. 5. For tubes, etc. 4. a good conductor of heat and electricity. 5. It melts at 1083°C NON-FERROUS METALS Tin Tin is a very important non-ferrous metal which is Uses of Tin obtained from ore, tin pyrites or tinstone. 1. Used for plating. Properties of Tin 2. For lining and lead pipes. 1. When a bar of tin is bent, a peculiar noise 3. For making alloys and solders. takes place which is known as a cry of tin. 4. For making trunks, boxes, cans, pans, etc. 2. white metal with brilliant luster. 3. soft and malleable. 4. withstands corrosion due to acids. 5. melts at 232°C. NON-FERROUS METALS Zinc Zinc is one of the most extensively used 4. can be rolled into sheets. non-ferrous metals. Occurs in wide variety of 5. melting point is 420°C combination in nature. Zinc is manufactured from ores by roasting and subsequent distillation with carbon. Uses of Zinc Properties of Zinc 1. Used for galvanizing steel sheets. 1. bluish white metal. 2. For making roofing sheets, pipes, ventilators. 2. easily fused. 3. Used in brass making. 3. brittle when cold, but malleable at a high 4. For making negative poles of batteries. temperature. NON-FERROUS METALS Lead Lead is extracted from galvena ores. It is a very Uses of Lead cheap, but useful nonferrous metal. It is produced 1. For making shots and bullets. from the ores by smelting in a reverberatory furnace. 2. Used for making gas pipes. Properties of Lead 3. Printers type letters. 1. very soft, heavy blush grey in color. 4. Flushing tank. 2. can be easily cut with a knife. 5. Roof covers. 3. makes impression on paper. 4. melting point is 327° and boiling point is 1600° C. SUPER ALLOYS Three Groups of Superalloys 1. Iron-based alloys - in some cases iron is less than 50% of total composition 2. Nickel-based alloys - better high temperature strength than alloy steels 3. Cobalt-based alloys - ~ 40% Co and ~ 20% chromium SUPER ALLOYS Importance: ◼ Room temperature strength properties are good in comparison to other metals, but not outstanding ◼ High temperature performance is excellent – tensile strength, hot hardness, creep resistance, and corrosion resistance at very elevated temperatures ◼ Operating temperatures often in the vicinity of 1100°C (2000°F) ◼ Have many applications Example is that it is used in systems in which operating efficiency increases with higher temperatures e.g., gas turbines, jet and rocket engines, steam turbines, and nuclear power plants SUPER ALLOYS Importance: ◼ Room temperature strength properties are good in comparison to other metals, but not outstanding ◼ High temperature performance is excellent – tensile strength, hot hardness, creep resistance, and corrosion resistance at very elevated temperatures ◼ Operating temperatures often in the vicinity of 1100°C (2000°F) ◼ Have many applications Example is that it is used in systems in which operating efficiency increases with higher temperatures e.g., gas turbines, jet and rocket engines, steam turbines, and nuclear power plants METAL PROCESSING ◼ processing of metals should be carried out carefully ◼ Affects the mechanical properties of metals Grain Size Effect ◼ Grains in metals tend to grow larger as the metal is heated ◼ metals with small grains are stronger but they are less ductile METAL PROCESSING Quenching and Hardening ◼ Most steels may be hardened by heating and cooling rapidly (quenching) ◼ metals are quenched in water or oil ◼ Produce very hard but brittle metal Annealing ◼ a softening process in which metals are heated and then allowed to cool slowly Tempering ◼ heating a hardened metal and allowing it to cool slowly ◼ produce a metal that is still hard and less brittle ◼ results formation of small Fe3C (iron carbide or cementite) precipitates in the steel, which provides strength METAL PROCESSING Cold Working ◼ refers to the process of strengthening a metal by changing its shape without the use of heat ◼ also known as plastic deformation or work hardening, involves strengthening a metal by changing its shape. ◼ the metal is subjected to mechanical stress so as to cause a permanent change to the metal's crystalline structure METAL PROCESSING Cold Working METAL MANUFACTURING: PRODUCTION CASTING ◼ Melting and molding - molten metal is poured into a mold cavity where, the metal take on the shape of the cavity once it cools ◼ For small intricate parts (Dies, jewelry, plaques, and machine components ) ◼ SHOULD NOT be used for products that require high strength, high ductility, or tight tolerances a. Expendable Mold Casting - the mold must be destroyed in order to remove the part b. Permanent Mold Casting - the mold is fabricated out of a ductile material and can be used repeatedly. METAL MANUFACTURING: PRODUCTION Powder Processing ◼ treats powdered metals with pressure (pressing) and heat (sintering) to form different shapes ◼ Powdered metallurgy (processing of powdered metals) is known for its precision and output quality – it keeps tight tolerances and often requires no secondary fabrications metal powder is compacted into the desired shape and heated to cause the particles to bond into a rigid mass. incredibly costly and generally only used for small, complex parts Powder processing is NOT appropriate for high-strength applications. METAL MANUFACTURING: PRODUCTION Powder Processing ◼ treats powdered metals with pressure (pressing) and heat (sintering) to form different shapes ◼ Powdered metallurgy (processing of powdered metals) is known for its precision and output quality – it keeps tight tolerances and often requires no secondary fabrications metal powder is compacted into the desired shape and heated to cause the particles to bond into a rigid mass. incredibly costly and generally only used for small, complex parts Powder processing is NOT appropriate for high-strength applications. METAL MANUFACTURING: PRODUCTION Forming ◼ raw metal (usually in sheet metal form) is mechanically manipulated into a desired shape ◼ Unlike casting, metal forming allows for higher strength, ductility, and workability for additional fabrications METAL MANUFACTURING: FABRICATION Deformation ◼ bending, rolling, forging, and drawing ◼ Deformation processes include metal forming and sheet metalworking Application of stresses to the piece which exceed the yield stress of the metal ◼ There are two types of deformation processes: a. Bulk Processes - characterized by large deformations and shape changes surface area to volume ratio is relatively small include rolling, forging, extrusion and wire and bar drawing. b. Sheet Metalworking - performed on metal sheets, strips and coils having a high surface area to volume ratio. use a punch and die to form the workpiece Bending, drawing and shearing METAL MANUFACTURING: FABRICATION Machining ◼ any fabrication method that removes a section of the metal ◼ also known as material removal processing ◼ Cutting, shearing, punching, and stamping are all common types of machining fabrication. a. Machining Operations - These are cutting operations using cutting tools that are harder than the metal of the product. They include turning, drilling, milling, shaping, planning, broaching and sawing. b. Abrasive Machining - In these methods material is removed by abrasive particles that normally form a bonded wheel. Grinding, honing and lapping are included in this category. c. Nontraditional Processes - These methods use lasers, electron beams, chemical erosion, electric discharge and electrochemical energy instead of traditional cutting and grinding tools When planning for machining in your supply chain, hardening processes should happen AFTER machining processes. Hardened metals have a high shear strength and are more difficult to cut. METAL MANUFACTURING: FABRICATION Joining ◼ Joining, or assembly, is one of the last steps of the metal manufacturing process ◼ includes welding, brazing, bolting, and adhesives. ◼ Assembly can be done by machine or by hand, where multiple parts are connected either permanently or semi-permanently to form a new entity. Finishing ◼ includes everything from galvanization to powder coating, and can take place throughout the manufacturing process MECHANICAL PROPERTIES OF MATERIALS Strength ◼ It is the capacity of the material to withstand the breaking, bowing, or deforming under the action of mechanical loads on it. Elasticity ◼ It is the property of a material to come back to its original size and shape even after the load stops acting on it. Plasticity ◼ It is the property of a material that makes it to be in the deformed size and shape even after the load stops acting on it. Ductility ◼ It is the property of a material that allows it to deform or make into thin wires under the action of tensile loads plastically. Tensile strength ◼ It is the property of a material that allows it to deform under tensile loading without breaking under the action of a load STRENGTH OF MATERIALS NORMAL STRESS ◼ either tensile stress or compressive stress ◼ Tension or tensile force applied results to Tensile Stress (increase in length) ◼ Compression or compressive force applied results to Compressive Stress (decrease in ◼ length) STRENGTH OF MATERIALS ◼ ◼ STRENGTH OF MATERIALS ◼ ◼ STRENGTH OF MATERIALS ◼ STRENGTH OF MATERIALS STRESS-STRAIN DIAGRAM ◼ the graph of quantities with the stress σ along the y-axis and the strain ε ◼ differs in form for various materials ◼ Metallic engineering materials are classified as either ductile or brittle ◼ Ductile material is one having relatively large tensile strains up to the point of rupture like structural steel and aluminum ◼ Brittle materials have a relatively small strain up to the point of rupture like cast iron and concrete. STRENGTH OF MATERIALS ◼ STRENGTH OF MATERIALS STRESS-STRAIN DIAGRAM Elastic Limit (E) ◼ limit beyond which the material will no longer go back to its original shape when the load is removed Elastic and Plastic Ranges ◼ The region in stress-strain diagram from O to P is called the elastic range. The region from P to R is called the plastic range Yield Point ◼ Yield point is the point at which the material will have an appreciable elongation or yielding without any increase in load STRENGTH OF MATERIALS STRESS-STRAIN DIAGRAM Ultimate Strength ◼ The maximum ordinate in the stress-strain diagram is the ultimate strength or tensile strength Rapture Strength ◼ Rapture strength is the strength of the material at rupture. This is also known as the breaking strength