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ENGINEERING MATERIALS

ENGINEERING MATERIALS. IRON & STEEL – THEIR PRODUCTION. IRON AND STEELS - THEIR PRODUCTION. Iron was first used by man for the manufacture of tools and weapons more than three thousands years ago.

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ENGINEERING MATERIALS

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  1. ENGINEERING MATERIALS

  2. IRON & STEEL – THEIR PRODUCTION

  3. IRON AND STEELS - THEIR PRODUCTION Iron was first used by man for the manufacture of tools and weapons more than three thousands years ago. Iron ores are relatively abundant and are widely distributed throughout the world. The availability, comparatively low cost and wide range of properties have made irons and steels materials of great importance. In the first industrial revolution in the mid of 18th century, cast and wrought iron were the main construction materials. The invention of the Bessemer converter in 1856, and other developments in the later years mass production of steels with consistent quality were taken place.

  4. BESSEMER CONVERTER 2

  5. IRON AND STEELS - THEIR PRODUCTION Use of chromium and nickel alloy steels were first produced just over last 100 years and since then the pace of development has been rapid. Now today a very large range of steels with enhanced properties are available for use for even very complicated situation. Irons and steels account for more than 90 per cent of the total tonnage of all metals used today mainly because of their combination of good strength, toughness, and ductility. Metal alloys are mainly grouped into two categories of Ferrous Alloys and Non-Ferrous Alloys.

  6. IRON ORE AND ITS EXTRACTION Most iron is extracted from iron ores in large blast furnaces. In the blast furnace coke (carbon) acts as a reducing agent to reduce iron oxides to produce raw pig iron which contains about 4% of carbon, 2% silicon, 1% manganese, 0.5% sulphur and in many cases phosphorus up to 2%. When the liquid iron from blast furnace is cast into ingots it is referred as Pig Iron. The pig iron from the blast furnace is usually transferred in the liquid state to a steel-making furnace. At the end of the refining process the amounts of carbon, silicon, manganese, sulphur and phosphorus in the iron will be very small, less than 0.05% of each, and iron will be in a highly oxidized state.

  7. BLAST FURNCACE 2

  8. REFINEMENT OF STEEL FROM ORE 2

  9. PRODUCTION OF CAST IRONS & STEELS Pig iron is remelted and used to make cast products (cast iron), however, bulk of blast furnace production is converted into steel. Cast irons are a family of ferrous alloys with a wide range of properties. Selected grades of pig iron is casted into the desired shape in sand moulds and such is their name. The carbon content in cast irons is generally between 2 to 4% and 1 to 3% silicon. Other alloying elements may also be present to control or vary certain properties. Cast irons make excellent casting alloys since they are easily melted, are very fluid in the liquid state. Cast irons solidify with slight to moderate shrinkage during casting and cooling. Cast irons have wide range of strengths and hardness and in most cases are easy to machine. These can be alloyed to produce superior wear, abrasion, and corrosion resistance.

  10. CAST IRONS & THEIR TYPES Cast irons, however, have relatively low impact resistance and ductility, and this limits their use of some applications. The wide industrial use of cast irons is due mainly to their comparatively low cost and versatile engineering properties. There are following five types of cast irons which can be differentiated from each other by the distribution of carbons in their microstructures. White Cast Iron Gray Cast Iron Malleable Cast Iron Ductile Cast Iron High Alloy Cast Iron

  11. White cast iron is formed when much of the carbon in a molten cast iron on solidification forms iron carbide instead of graphite. White cast irons are so called because they fracture to produce a “white” or bright crystalline fractured surface. White cast iron contains 2.5 – 3.0% of carbon and 0.5 – 1.5% of silicon. White cast irons are most often used for their excellent resistance to wear and abrasion. White cast iron also serves as the raw material for malleable cast irons. Gray cast iron also forms on solidification in a specific way. The fractured surface of gray cast iron appears gray because of the exposed graphite. Gray cast iron is an important engineering material because of its relatively low cost and useful engineering properties such as excellent machinability at hardness levels that have good wear resistance and excellent vibrational damping capacity

  12. Malleable cast irons are first cast as white cast irons that contain large amounts of iron carbides and no graphite. There is 2.0 – 2.6% of carbon and 1.1 – 1.6% of silicon in malleable cast iron. Malleable cast irons are important engineering materials since they have the desirable properties of castability, machineability, moderate strength, toughness, corrosion resistance for certain applications. Ductile cast iron combines the processing advantages of gray cast iron with the engineering advantages of steel. Carbon content is from 3.0 – 4.0% and silicon is present from 1.8 – 2.0 %. Ductile cast irons have good fluidity & castability, excellent machinability, and good wear resistance.. This type of iron also has properties such as high strength, toughness, ductility, hot workability and hardenability.

  13. High alloy cast irons are produced by adding other elements in handsome amount such as chromium, nickel and molybdenum. Addition of these metals produce desirable properties such as high strength, hard and abrasion resistance, corrosion resistance and as well as high temperature resistance. The addition of 5% of nickel produces a martensitic structure which makes this type of iron very suitable for the manufacture of metal working rolls. The best irons for corrosion resistance are those which have 15 – 20% of nickel. This type of iron has austenitic structure and are non-magnetic.

  14. IRON ORE AND ITS EXTRACTION Steel making process is basically a oxidation process in which the present impurities in iron are oxidized away. This process is carried out in a larger converter using oxygen as the oxidizing agent or in electric arc furnace. At the end of the refining process the amounts of carbon, silicon, manganese, sulphur and phosphorus in the iron will be very small, less than 0.05%. At this stage iron is in a highly oxidized state. For producing steels the liquid metal must be deoxidized and for this purpose silicon and manganese are added in sufficient quantity to leave some residual silicon and manganese in the steel. Aluminium is also used as oxidizing agent.

  15. PRODUCTION OF STEELS Steels are essentially alloys of iron and carbon but they will contain some silicon and manganese, traces of sulphur and phosphorus and also may contain other elements such nickel or chromium as alloying additions. Plain Carbon or Non Alloy steels are steels containing up to 1.5% of carbon together with not more than 0.5% of silicon and not more than 1.5% of manganese, and with only traces of other elements. Plain Carbon steels are further divided into further categories of mild or low carbon steels, medium carbon steels, and high carbon steels or tool steels.

  16. PRODUCTION OF STEELS Mild or low carbon steels contain up to 0.3% of carbon, medium carbon steels contain carbon between 0.3 to 0.6% and high carbon steels have more 0.6% of carbon. Plain-carbon steels are most commonly designated by a four-digit AISI-SAE code. The first two digits are 10 which indicate that the steel is a plain-carbon steel. The last two digits indicate the nominal content of the steel in hundredths of a percent. All plain-carbon steels contain manganese as an alloying element to enhance strength. The content of this alloy ranges from 0.30 to 0.95% in plain-carbon steels. Plain-carbon steels also contain impurities of sulfur, phosphorus, silicon, and some other elements.

  17. PRODUCTION OF STEELS Very low carbon plain-carbon steels have relatively low strengths but very high ductilities. These steels are used for sheet material for forming applications such as fenders and body panels for automobiles. With increasing the content of carbon in plain-carbon steels, steels become stronger but less ductile. Medium-carbon steels find applications for the shafts and gears. High carbon steels are used for springs, die blocks, cutters and shear blades. Plain-carbon steels are relatively low in cost but have some limitations such as low corrosion and oxidation resistance, poor impact resistance at low temperature etc.

  18. PRODUCTION OF STEELS In order to overcome the deficiencies of plain-carbon steels, alloy steels have been developed by adding different elements such as manganese, nickel, chromium, molybdenum and tungsten. Some other elements are also added. Alloy steels may contain up to 50% of alloying elements. These steels are mainly automotive and construction type steels. Alloy steels are usually designated by the four-digit AISI-SAE system. The first two digits designate the principal alloying element or groups of elements and the last two digits indicate the hundredths of percentage of carbon in alloying steels.

  19. PRODUCTION OF STEELS Alloy Steels are steels that contain either silicon or manganese in amounts in excess of the values as mentioned above, or that contain any other element or elements. Alloy steels can further be divided into main groups – low alloy and high alloy steels. Alloy Steels are steels that contain either silicon or manganese in amounts in excess of the values as mentioned above, or that contain any other element or elements. Alloy steels can further be divided into main groups – low alloy and high alloy steels. Low alloy steels contain up to 3 to 4% of one or more alloying elements while high alloy steels are those which have more 5% of alloy content.

  20. PRODUCTION OF STEELS Low alloy steels have enhanced properties such as increased strength without loss of toughness and increased hardenability. The application of low alloy steels are similar to plain carbon steels of equivalent carbon content. A major group of low alloy steels is the high-strength low-alloy steels (HSLA) which are the strongest and toughest steels and have been developed by making micro-alloying additions of aluminium, niobium and vanadium. Another important range of structural steels are those low alloy steels which are weather resistant. Unlike other steels, after exposure to wind and rain, these do not corrode with the formation of the usual porous and flaky rust deposit.

  21. High alloy steels are those which differ considerably from those of plain-carbon steels. In general these alloy steels have more than 5% of alloying elements. These alloys have very excellent properties as compared to plain-carbon and low alloy steels. These are very hard and can maintain their hardness up to 600 degrees C. These are the hardest, strongest, and yet least ductile of the carbon steels. These are used in hardened and tempered conditions for sharp cutting tools. These are also used for dies form forming and shaping materials. These materials can give tensile strength of up to 1900 MPa. These can become very soft and machineable with ease after some heat treatment. These have high resistance to abrasion.

  22. STAINLESS STEELS Stainless steels are selected as engineering materials mainly because of their excellent corrosion resistance in very aggressive environments. This anti corrosion resistance is because of added material of chromium. In order to make steels as stainless steels at least 12% of chromium content is required. In fact chromium forms a surface oxide that prevents the such steels from corroding. Corrosion resistance may also be enhanced by adding nickel and molybdenum elements. A wide range of mechanical properties along with excellent corrosion and elevated temperature resistance make stainless steels very much suitable and versatile in their applicability for different engineering applications.

  23. There are following main three types of stainless steels depending upon the predominant phase constituent of the microstructures: Ferritic Stainless Steels Martensitic Stainless Steels Austenitic Stainless Steels Ferritic stainless steels are basically iron-chromium binary alloys containing about 12 to 30% of chromium. The ferritic stainless steels are relatively low in cost and are mainly used in construction industry. Martensitic stainless steels are essentially iron-chromium alloys containing 12 to 17% of chromium. These steels have the highest hardness of any corrosion resisting steel. This steel is used for machine parts such as pumps, shafts, bolts and bushings.

  24. Austenitic stainless steels are basically iron-chromium-nickel ternary alloys containing about 16 to 25% of chromium, and 7 to 20% nickel. Austenitic stainless steels have better corrosion resistance than ferritic and martensitic steels. These steels have high degree of formability as compared to other steels. All these stainless steels are frequently used for elevated temperature applications as they resist oxidation and maintain their mechanical integrity. Because of this particular property these are used in turbines, boilers, heat-treating furnaces, aircraft, missiles and also nuclear power generating units.

  25. QUESTIONS AND QUERIES IF ANY! IF NOT THEN GOOD BYE NEXT WOULD DISCUSSED NON FERROUS ALLOYS

  26. ASSIGNMENT N0. 03 Q. NO. 01 – HOW DO YOU GET CAST IRON FROM ORE IRON? WHY DO WE CALL IT CAST IRON? WHAT ARE ITS TYPES? Q. NO. 02 – WHAT IS THE PERCENTAGE OF CARBON IN DIFFERENT TYPES OF PLAIN CARBON STEELS? WRITE BRIEFLY ABOUT DIFFERENT TYPES OF CARBON STEELS. Q. NO. 03 – HOW DOES STAINLESS STEEL DIFFER FROM CAST IRON AND PLAIN CARBON STEELS? WHAT ARE THE SPECIFIC PROPERTIES OF STAINLESS STEEL?

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