Engineering Materials

1. Engineering Materials HaseebUllah Khan Jatoi Department of Chemical Engineering UET Lahore

2. Iron and Steel

3. Metal Alloy • An alloy is a mixture or metallic solid solution composed of two or more elements. • An alloy will contain one or more of the three: a solid solution of the elements (a single phase); a mixture of metallic phases (two or more solutions); an inter-metallic compound with no distinct boundary between the phases. • May or may not be homogenous depending upon thermal history of the material • May be substitution alloy, or interstitial alloy • Brass (Copper + Zinc) • Pewter (Tin 85-99% + Copper + Antimony + Bismuth) • Phosphor Bronze (Copper + Tin + Phosphorus) • Amalgam ( Mercury + Metal)

4. Phase Diagram • To understand design and control of heat treating procedures • To understand properties and microstructure of alloys • Components (Pure constituents) • System (E.g. Iron-Carbon System) • Solubility Limit (May be temp dependent or composition etc.) • Phase (homogenous portion of system having uniform physical and chemical properties) • Homogenous and heterogeneous • Most metallic alloys are heterogeneous

6. Microstructure of alloy • Microstructure is subject to direct microscopic observation, using optical or electron microscopes • Depends on: • Alloying elements present • Their concentration • Heat treatment of alloy (Temperature, heating time, cooling rate)

7. Phase Diagram • Temperature , Pressure, and Composition are three parameters that are played • One component diagram (Unary) • Two component diagram (Binary) • Multi-component diagram

8. Single phase

9. Binary system

10. L = homogeneous liquid solution composed of both copper and nickel • α= substitution solid solution consisting of both copper and nickel • Liquidus and solidus • Two extremities represent melting temperatures of two components

11. Information from phase diagram • Phases present • Phase composition (Tie Line) • Phase amounts (Lever Rule)

13. Exercise

14. Microstructure (Cooling or solidification)

15. Eutectic phase diagram • α= solid solution rich in copper or pure copper • β = solid solution rich in silver or pure silver • Eutectic (easily melted) point and eutectic reaction • Solvus, solidus, liquidus, invariant point

17. Metal Alloys Classification

18. Ferrous Alloys • Iron is the prime constituent • Produced largely and abundantly used as engineering construction materials • ‘All-purpose alloys’, but one big disadvantage i.e. Corrosion. • Why prefer ferrous alloys? • Iron-containing compounds exist in abundant quantities within the earth’s crust ( ores are cheaper) • Metallic iron and steel alloys may be produced using relatively economical extraction, refining, alloying, and fabrication techniques • They are extremely versatile (can be fashioned to have versatile desired properties)

19. Iron and Steel production • Iron making – Iron is reduced from its ores • Steel making – Iron is then refined to obtain desired purity and composition (Alloying)

20. Iron Ores required in Iron making • The principal ore used in the production of iron and steel is hematite (Fe2O3) • Other iron ores include magnetite (Fe3O4), siderite (FeCO3), and limonite (Fe2O3-xH2O, where x is typically around 1.5) • Iron ores contain from 50% to around 70% iron, depending on grade (hematite is almost 70% iron) • Scrap iron and steel are also widely used today as raw materials in iron and steel making

21. Iron Ores

22. Other Raw Materials in Iron-making • Coke • Supplies heat for chemical reactions and produces carbon monoxide (CO) to reduce iron ore

23. Limestone (CaCO3) • Used as a flux to react with and remove impurities in molten iron as slag • Hot gases (CO, H2, CO2, H2O, N2, O2, and fuels) • Used to burn coke

24. Iron-making in a Blast Furnace • Blast furnace - a refractory-lined chamber with a diameter of about 9 to 11 m (30 to 35 ft) at its widest and a height of 40 m (125 ft) • To produce iron, a charge of ore, coke, and limestone are dropped into the top of a blast furnace • Hot gases are forced into the lower part of the chamber at high rates to accomplish combustion and reduction of the iron

25. Blast Furnace

26. Chemical Reactions in Iron-Making • Using heated air (O2) with coke: 2C + O2 heat + 2CO • Using hematite as the starting ore: Fe2O3 + CO 2FeO + CO2 • CO2 reacts with coke to form more CO: CO2 + C (coke) 2CO • This accomplishes final reduction of FeO to iron: FeO + CO Fe + CO2

27. Iron from the Blast Furnace • Iron tapped from the blast furnace (called pigiron) contains over 4% C, plus other impurities: 0.3-1.3% Si, 0.5-2.0% Mn, 0.1-1.0% P, and 0.02-0.08% S • Further refinement is required for cast iron and steel • A furnace called a cupola is commonly used for converting pig iron into graycastiron • For steel, compositions must be more closely controlled and impurities brought to much lower levels

28. Steel-making • Since the mid-1800s, a number of processes have been developed for refining pig iron into steel • Today, the two most important processes are – Basic oxygen furnace (BOF) – Electric furnace • Both are used to produce carbon and alloy steels

29. Basic Oxygen Furnace (BOF) • Accounts for almost 70% of steel production in U.S • Adaptation of the Bessemer converter • Bessemer process used air blown up through the molten pig iron to burn off impurities • BOF uses pure oxygen • Typical BOF vessel is typically 5 m (16 ft) inside diameter and can process 150 to 200 tons per heat • Cycle time (tap-to-tap time) takes almost 45 min

30. Basic Oxygen Furnace

31. Electric Arc Furnace • Accounts for 30% of steel production in U.S. • Scrap iron and scrap steel are primary raw materials • Capacities commonly range between 25 and 100 tons per heat • Complete melting requires about 2 hr; tap-to-tap time is 4 hr • Usually associated with production of alloy steels, tool steels, and stainless steels • Noted for better quality steel but higher cost per ton, compared to BOF

32. Electric arc furnace

33. Casting Processes in Steel-making • Steels produced by BOF or electric furnace are solidified for subsequent processing either as cast ingots or by continuous casting • – Casting of ingots – a discrete production process • – Continuous casting – a semi-continuous process

34. Casting of Ingots • Steel ingots = discrete castings weighing from less than one ton up to 300 tons (entire heat) • Molds made of high carbon iron, tapered at top or bottom for removal of solid casting • The mold is placed on a platform called a stool • After solidification the mold is lifted, leaving the casting on the stool

37. Continuous Casting • Continuous casting is widely applied in aluminum and copper production, but its most noteworthy application is steel-making • Dramatic productivity increases over ingot casting, which is a discrete process • For ingot casting, 10-12 hr may be required for casting to solidify • Continuous casting reduces solidification time by an order of magnitude

41. Steel • An alloy of iron containing from 0.02% and 2.11% carbon by weight • Often includes other alloying elements: nickel, manganese, chromium, and molybdenum • Steel alloys can be grouped into four categories: 1. Plain carbon steels 2. Low alloy steels 3. Stainless steels 4. Tool steels

42. Next Lecture • Steel and its application in chemical engineering