Ms chapter 3


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Ms chapter 3

  1. 1. 1. Describes in simple terms the production of pig iron from iron ore2. Describe the principles of the open-hearth, the Bessemer and more modern processes used in the production of steel from pig iron3. Explains the principal differences between sand casting, die casting, centrifugal casting, forgings, cold working and hot-rolled plate, bars and other sections4. States the normal range of carbon content in mild steel, tool steel, cast steel and cast iron5. Describe the principle difference between ferrous and non ferrous metals6. Gives examples of applications of non-ferrous metals in marine engineering7. States the purpose of the alloying elements nickel, chromium and molybdenum in steels used in marine engineering8. Identifies the metals used in non-ferrous alloys commonly employed in marine engineering
  2. 2. Metallurgy is a domain of materials science that studies the physicaland chemical behavior of metallic elements, their intermetalliccompounds, and their compounds, which are called alloys. It is also the technology of metals: the way in which science isapplied to their practical use.Metallurgy is commonly used in the craft of metalworking.The differences between the various types of iron and steel aresometimes confusing because of the nomenclature used.Steel in general is an alloy of iron and carbon, often with an admixtureof other elements.Some alloys that are commercially called irons contain more carbonthan commercial steels.
  3. 3. Open-hearth iron and wrought iron contain only a few hundredthsof 1 percent of carbon.Steels of various types contain from 0.04 percent to 2.25 percent ofcarbon.Cast iron, malleable cast iron, and pig iron contain amounts ofcarbon varying from 2 to 4 percent.A special form of malleable iron, containing virtually no carbon, isknown as white-heart malleable iron.A special group of iron alloys, known as ferroalloys, is used in themanufacture of iron and steel alloys; they contain from 20 to 80percent of an alloying element, such as manganese, silicon, orchromium.
  4. 4. The production of iron or steel is a process:3. The first stage is to produce pig iron in a blast furnace.5. The second is to make wrought iron or steel from pig iron by a further process.To make iron, you start with iron ore. Iron ore is simply rock thathappens to contain a high concentration of iron.Common iron ores include:Hematite - Fe2O3 - 70 percent ironMagnetite - Fe3O4 - 72 percent ironLimonite - Fe2O3 + H2O - 50 percentto 66 percent ironSiderite - FeCO3 - 48 percent iron
  5. 5. Creating IronAs see in the previous section that all of the iron ores contain ironcombined with oxygen. To make iron from iron ore, we need toeliminate the oxygen to create pure iron.The most primitive facility used to refine iron from iron ore is called abloomery. In a bloomery, charcoal is burnt with iron ore and a goodsupply of oxygen (provided by a bellows or blower).Charcoal is essentially pure carbon. The carbon combines with oxygento create carbon dioxide and carbon monoxide (releasing lots of heatin the process). Carbon and carbon monoxide combine with theoxygen in the iron ore and carry it away, leaving iron metal.
  6. 6. In a bloomery, the fire does not get hot enough to melt the ironcompletely, it left with a spongy mass containing iron and silicatesfrom the ore (the bloom).By heating and hammering the bloom, the glassy silicates mix intothe iron metal to create wrought iron. Wrought iron is tough and easyto work, making it perfect for creating tools in a blacksmith shop.The more advanced way to smelt iron is in a blast furnace. A blastfurnace is charged with iron ore, charcoal or coke (coke is charcoalmade from coal) and limestone (CaCO3).Huge quantities of air blast in at the bottom of the furnace. Thecalcium in the limestone combines with the silicates to form slag. Atthe bottom of the blast furnace, liquid iron collects along with a layerof slag on top. Periodically, let the liquid iron flow out and cool.
  7. 7. The liquid iron typically flows into a channel and indentations in abed of sand. Once it cools, this metal is known as pig iron.To create a ton of pig iron, start with 2 tons of ore, 1 ton of coke andhalf-ton of limestone. The fire consumes 5 tons of air. Thetemperature reaches almost 3000 degrees F (about 1600 degrees C) atthe core of the blast furnace.Pig iron contains 4 percent to 5 percent carbon and is so hard andbrittle that it is almost useless. Thus melt the pig iron, mix it withslag and hammer it to eliminate most of the carbon (down to 0.3percent) and create wrought iron. Wrought iron is the stuff ablacksmith works with to create tools, horseshoes and so on. Whenheat the wrought iron, it is malleable, bendable, weldable and veryeasy to work with.
  8. 8. Blast Furnace
  9. 9. ModernFurnace
  10. 10. Description:1. Hot blast from Cowper stoves2. Melting zone3. Reduction zone of ferrous oxide4. Reduction zone of ferric oxide5. Pre-heating zone6. Feed of ore, limestone and coke7. Exhaust gases8. Column of ore, coke and limestone9. Removal of slag10. Tapping of molten pig iron11. Collection of waste gases
  11. 11. Creating SteelSteel is iron that has most of the impurities removed. Steel also has aconsistent concentration of carbon throughout (0.5 percent to 1.5percent).Impurities like silica, phosphorous and sulfur weaken steeltremendously, so they must be eliminated. The advantage of steel overiron is greatly improved strength.The open hearth furnace is one way to create steel from pig iron. Thepig iron, limestone and iron ore go into an open hearth furnace. It isheated to about 1600 F (871 C).The limestone and ore forms a slag that floats on the surface.Impurities, including carbon, are oxidized and float out of the iron intothe slag. When the carbon content is right, you have carbon steel.
  12. 12. Another way to create steel from pig iron is the Bessemer process.Most modern steel plants use whats called a basic oxygen furnaceto create steel. The advantage is that it is a rapid process -- about 10times faster than the open hearth furnace.A variety of metals might be alloyed with the steel at this point tocreate different properties. For example, the addition of 10 percentto 30 percent chromium creates stainless steel, which is veryresistant to rust. The addition of chromium and molybdenum createschrome-moly steel, which is strong and light.When you think about it, there are two accidents of nature that havemade it much easier for humans to move forward at a rapid pace.One is the huge availability of something as useful as iron ore. Thesecond is the availability of vast quantities of oil and coal to powerthe production of iron. This is a very lucky coincidence, becausewithout iron and energy, we would not have gotten nearly as far aswe have today
  13. 13. Question:Describe the principles of the Bessemer and basic oxygen usedin the production of steel from pig iron.Due date: 20th November 2008 (before 1700 hrs)Assessment: 5%
  14. 14. Casting is the process whereby molten material is poured into amould of the required shape and then allowed to solidify.Moulding is a similar process used to form plastic materials. Themould should be shaped so that molten material flows to all parts ofthe mould.AdvantagesThis process is widely used as a primary forming process andsuitable for bulk shaping of a material.DisadvantagesThe shape of the finished casting may be different to the shape of themould because metals shrink as they cool.
  15. 15. Considerations when selecting a method of casting2.The type of casting process most suitable for a particularapplication is dictated by a number of factors. These include:3.The number of castings4.The cost per casting5.The material being cast6.The surface finish and tolerances of the finished casting7.The size of the castingCasting MethodsTypical casting processes include:Sand castingDie castingCentrifugal casting
  16. 16. Sand Casting involves packing a moulding material (traditionally amixture of sand and clay) around a pattern of the casting. This is usuallymade of a hardwood and will be larger than the requirements of thefinished casting to allow for shrinkage. The mould is then split so thatthe pattern can be removed.AdvantagesThis process can be used for a large range of sizes and for small or largeproduction runs. It is the cheapest casting process available for smallproduction runs and can sometimes be economical for large productionruns.DisadvantagesThe surface finish and tolerances of the finished casting are poor. Thisform of casting can significantly alter the mechanical properties of thematerial being cast. The time required to cast a components can beexcessive due to the need to allow the casting to cool before removing itfrom the mould.
  17. 17. Die casting uses a metal mould into which molten metal is poured andallowed to solidify.There are two main methods of feeding the molten metal into the mould:1. Gravity die casting uses the force of gravity to draw the molten metaldown into the mould.2. Pressure die casting involves forcing the molten metal into the mouldunder pressure. Using pressure die casting enables more complex shapesto be cast ensuring the molten metal flows to all corners of the mould.AdvantagesMachining and finishing costs can significantly reduce or eveneliminated because of the relatively good dimensional tolerances andsurface finish achieved using this processAll casting alters the physical properties of the material, but using thisdie casting this can be minimised.
  18. 18. DisadvantagesThis process too expensive for small production runs because of thehigh cost of producing the mould.Its use is restricted to metals with lower melting points (E.g.magnesium, aluminium) than the mould metalAluminum, Zinc and Copper alloys are the materials predominantlyused in die-casting.On the other hand, pure Aluminum is rarely cast due to high shrinkage,and susceptibility to hot cracking. It is alloyed with Silicon, whichincreases melt fluidity, reduces machinability.Copper is another alloying element, which increases hardness, reducesductility, and reduces corrosion resistance.
  19. 19. Aluminum is cast at a temperature of 650 ºC (1200 ºF).It is alloyed with Silicon 9% and Copper about 3.5% to form theAluminum Association 380 alloy (UNS A03800).Silicon increases the melt fluidity, reduces machinability.Copper increases hardness and reduces the ductility.By greatly reducing the amount of Copper (less than 0.6%) thechemical resistance is improved; thus, AA 360 (UNS A03600) isformulated for use in marine environments.A high silicon alloy is used in automotive engines for cylindercastings, AA 390 (UNS A03900) with 17% Silicon for high wearresistance.
  20. 20. Zinc can be made to close tolerances and with thinner walls thanAluminum, due to its high melt fluidity.Zinc is alloyed with Aluminum (4%), which adds strength andhardness.The casting is done at a fairly low temperature of 425 ºC (800 ºF)so the part does not have to cool much before it can be ejected fromthe die.This, in combination with the fact that Zinc can be run using a hotchamber process allows for a fast fill, fast cooling (and ejection)and a short cycle time. Zinc alloys are used in making precision parts such as sprockets,gears, and connector housings.
  21. 21. Copper alloys are used in plumbing, electrical and marineapplications where corrosion and wear resistance is important.Minimum wall thicknesses and minimum draft angles for diecasting are:
  22. 22. Die-castings are typically limited from 20 kg (55 lb) max. forMagnesium, to 35 kg (77 lb) max. for Zinc.Large castings tend to have greater porosity problems, due to entrappedair, and the melt solidifying before it gets to the furthest extremities ofthe die-cast cavity. The porosity problem can be somewhat overcomeby vacuum die casting.From a design point of view, it is best to design parts with uniformwall thicknesses and cores of simple shapes.Heavy sections cause cooling problems, trapped gases causingporosity.All corners should be radiused generously to avoid stressconcentration. Draft allowance should be provided to all for releasingthe parts-these are typically 0.25º to 0.75º per side depending on the
  23. 23. Object beenejected
  24. 24. In centrifugal casting, a permanent mold is rotated about its axis athigh speeds (300 to 3000 rpm) as the molten metal is poured.The molten metal is centrifugally thrown towards the inside moldwall, where it solidifies after cooling.Centrifugal force shapes the and feeds the molten metal into thedesigned crevices and details of the mold. The centrifugal forceimproves both homogeneity and accuracy of the casting.The casting is usually a fine grain casting with a very fine-grainedouter diameter, which is resistant to atmospheric corrosion, a typicalsituation with pipes.The inside diameter has more impurities and inclusions, which canbe machined away.
  25. 25. Only cylindrical shapes can be produced with this process.Size limits are upto 3 m (10 feet) diameter and 15 m (50 feet) length.Wall thickness can be 2.5 mm to 125 mm (0.1 - 5.0 in). Thetolerances that can be held on the OD can be as good as 2.5 mm (0.1in) and on the ID can be 3.8 mm (0.15 in). The surface finish rangesfrom 2.5 mm to 12.5 mm (0.1 - 0.5 in).Typical materials that can be cast with this process are iron, steel,stainless steels, and alloys of aluminum, copper and nickel.Two materials can be cast by introducing a second material duringthe process.Typical parts made by this process are pipes, boilers, pressurevessels, flywheels, cylinder liners and other parts that are axi-symmetric.
  26. 26. Advantages2.The centrifugal force ensures the mould is fully filled out withthe molten material.3.Rapid production rate.4.Ability to produce extremely large cylindrical parts.DisadvantagesNot suitable for casting complex shapes.
  27. 27. Forging is the process of shaping malleable metals by hammeringor pressing. The process refines the grain size and flow of the metaland so improves its structure.Forged metal is stronger and more ductile than cast metal andexhibits greater resistance to fatigue and impact.A forged metal can result in the following:• Increase length, decrease cross-section, called drawing out the metal.• Decrease length, increase cross-section, called upsetting the metal.• Change length, change cross-section, by squeezing in closed impression dies. Forging changes the size and shape, but not the volume, of a part.
  28. 28. Types of Forging1. Drop forging is a metal shaping process in which a heated workpiece is formed by rapid closing of a punch and die forcing the workpiece to conform to a die cavity. A workpiece may be forged by a series of punch and die operations (or by several cavities in the same die) to gradually change its shape. Drop forging is also called impression die or closed die forging, or rot forging.
  29. 29. 2. Upset forging is a metal shaping process in which a heated workpiece of uniform thickness is gripped between split female dies while a heading die (punch) is forced against the workpiece, deforming and enlarging the need of the workpiece. A sequence of die cavities may be used to control the workpiece geometry gradually until it achieves its final shape. This is a rapid "cold forming" process.
  30. 30. 3. Cold heading is defined as a "metal forging process used for rapidly producing enlarged (upset) sections on a piece of rod or wire held in a die." The resulting shape of the upset portion conforms to the shape of the die cavity. Workpieces are not heated prior to heading. Upsetting may be done in one or more strokes.
  31. 31. Cold working refers to plastic deformation that occurs usually, butnot necessarily, at room temperature. Plastic deformation is adeformation in which the material does not return to its originalshape; this is the opposite of an elastic deformation.Effects of Cold Working:The behavior and workability of themetals depend largely on whether deformation takes place below orabove the recrystallization temperature.Deformation using cold working results in:• Higher stiffness, and strength, but• Reduced malleability and ductility of the metal.
  32. 32. Hot working is the deformation that is carried out above therecrystallization temperature.In these circumstances, annealing takes place while the metal is workedrather than being a separate process.The metal can therefore be worked without it becoming work hardened.Hot working is usually carried out with the metal at a temperature ofabout 0.6 of its melting point.
  33. 33. Effects of hot working• At high temperature, scaling and oxidation exist. Scaling and oxidation produce undesirable surface finish. Most ferrous metals needs to be cold worked after hot working in order to improve the surface finish.• The amount of force needed to perform hot working is less than that for cold work.• The mechanical properties of the material remain unchanged during hot working.• The metal usually experiences a decrease in yield strength when hot worked. Therefore, it is possible to hot work the metal without causing any fracture.
  34. 34. Warm working: as the name implies, is carried out at intermediatetemperatures. It is a compromise between cold and hot working.The effects of this type of working depend on how close is the warmprocess to be a cold or hot process.The type of process chosen depends on the physical and mechanicalproperties needed for the product, meaning the product itself and itsuses.
  35. 35. Methods used for Cold, Hot working1. Rolling2. Forging3. Extrusion4. Drawing
  36. 36. Rolling is a fabricating process in which the metal, plastic, paper,glass, etc. is passed through a pair/pairs of rolls.There are two types of rolling process, flat and profile rolling.Rolling is also classified according to the temperature of the metalrolled. If the temperature of the metal is above its recrystallizationtemperature then the process is termed as hot rolling.If the temperature of metal is below its recrystallization temperaturethe process is termed as cold rolling.
  37. 37. In flat rolling the final shape of the product is either classed as sheet(typically thickness less than 3 mm, also called "strip") or plate(typically thickness more than 3 mm).
  38. 38. In profile rolling, the final product may be a round rod or othershaped bar such as a structural section (beam, channel, joist etc).
  39. 39. In the extrusion process, a billet (generally round) is forcedthrough a die in a manner similar to squeezing toothpaste from atube.Almost any solid or hollow cross-section may be produced byextrusion, which can create essentially semi-finished parts. Becausethe die geometry remains the same throughout the operation,extruded products have a constant cross-section. This can be donewith cold, warm or hot working.Typical products made by extrusion are railings for sliding doors,tubing having carious cross-sections, structural and architecturalshapes, and door and windows frames.
  40. 40. Drawing is an operation in which the cross-section of solid rod, wireor tubing is reduced or changed in shape by pulling it through a die.Drawn rods are used for shafts, spindles, and small pistons and as theraw material for fasteners such as rivets, bolts, screws.Drawing also improves strength and hardness when these propertiesare to be developed by cold work and not by subsequent heattreatment.