1. Engineering Materials
Haseeb Ullah 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. Hot gases (CO, H2, CO2, H2O, N2, O2, and fuels)
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 + O heat + 2CO
Using hematite as the starting ore:
Fe2O3 + CO FeO + CO2
CO2 reacts with coke to form more CO:
CO2 + C (coke) CO
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 pig iron) contains over 4% C, plus other impurities: % Si, % Mn, % P, and % S
Further refinement is required for cast iron and steel
A furnace called a cupola is commonly used for converting pig iron into gray cast iron
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, 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