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13) FERROUS METAL

Iron Steel Stainless steel

IRON

One of the most abundant metallic material in the earths crust (about 4-5%) Found in the form of ores as oxides, carbonates, silicates, and sulfides The most important iron-bearing minerals or iron ores are hematite and magnetite The most commonly used ore is Hematite (Fe2O3) Contains about 70% of pure iron Specific gravity in the range of 4.5 to 5.3

PRODUCTION OF IRON

Iron is produced in a blast furnace The main function of the blast furnace is to reduce

the ore to metal, followed by separation of themetal from the impurities

The iron ore in the form of pellets is charged intothe furnace with coke and limestone

The mined ore is crushed to small particles of size25 mm

These particles are further reduced to fine powder,which is later converted to pellets or sinters

Sintering is a process of application of neat thatresults in the conversion of fine ore into hard and

porous lumps (10 to 50 mm)

Pelletizing is a process of forming balls of 10 to 20mm in diameter in the presence of moisture and

additives such as bentonite or lime

Blast furnace

BLAST FURNACE

The main function of the blast furnace is to reduce the ore to metal, followed by the separation ofmetal from the impurities

In the furnace : Iron ore + coke + limestone Cokea carbonaceous solid produced from coal, petroleum, or other raw materials by thermaldecomposition Limestoneact as a flux that holds the silica and alumina impurities of the ore and coke A powerful air blast through the bottom raises the temperature sufficiently to burnt coke, melt iron,

and burn off oxygen

Temperature increases to 1650 C (3000 F), enough to melt the iron Molten iron collected at the bottom of the furnace (contain high carbon content), called as pig iron A nonmetallic product, consisting essentially silicates and aluminates of calcium and other bases, is

produced simultaneously with the molten iron

This product is called slag

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Pig Iron

Is not pure iron Saturated with carbon (3.5 to 4.5 % - taken from the coke) Contains manganese (0.25-1%), silicon(1-2%), and other materials Melting point 1670 C

Pure Iron

Carbon content0.010.02% Siliconless than 0.01% Manganese0.010.02 Melting point1535 C Tensile strength335 MPa

Steel Making Process

Iron Products

Come in three commercial forms1) Wrought iron (has the least carbon)2) Steel (0.25-1.7%)3) Cast iron (has the most carbon -5%)

Carbon affects the microstructure and properties of iron products

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STEEL

Is a combination of iron and carbon Carbon content may range between about 0.01 and 1% Manganese (less than 1.6%) Phosphorous, sulfur, and silicon (less than 0.6%) Produced in a basic oxygen furnace (BOF), open hearth furnace, or electric arc furnace

Steel alloys

The alloys are added to molten steel to produce steel of different characteristics, such as hardness,tensile strength, and toughness

Alloy materialsManganesegives strength and toughness to steelSiliconprovides strength and hardening propertiesChromium and nickelcorrosion resistant (stainless steel)Molybdenumimproves tensile and hardening properties

Steel Products

The semi-finishedproducts of

varying widths,

lengths, and

thickness

It comes in threetypes:

1)Blooms2)Slabs3)Billets

Iron-Bearing properties

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Steel Properties

Steel usually contain less than 1% carbon by weight. Structural steel has less than 0.25% by weight of carbon Manganese is the principal alloying element and is added when the steel is in the molten condition in

amounts up to about 1.6%

Carbon content

Affect the microstructure and properties of steel Increase in carbon content will:

Increase the hardness, strength, and abrasion resistance BUTDecrease the ductility, toughness, and impact resistanceDuctilitymeasured by the percent elongation during the tension testToughnessmeasured by he area under the stress-strain diagram

Effect of Carbon Content

Properties of Steel

Are greatly affected by three factors Chemical composition Heat treatment Mechanical workhot work, cold work

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Working Steel

Hot workingmechanical deformation at temperatures slightly above the transformation temperature Cold workingmechanical deformation at temperatures below the transformation temperature

(Transformation temperaturerecrystallization temperature)

Cold working increase the strength properties but decreases the ductilityMechanical Properties

Yield pointis a stress at which there is a marked increase in strain without an increase in strain Yield strengthis measured as stress corresponding to a known strain or an offset (proof stress)

Stress-Strain

Steel sections

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Structural shapes

Applications

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