Chapter 2:

Ferrous Metals

2.0 Iron Productions

1. Iron ores are main material in iron ingot production.

2. In mining process, the iron ore are in pure state. It also found

along with other substances such as oxide, sulphade, sulphur,

silicon, etc.

2.1 Types of Irons

2.2 Iron Ores Characteristics

1. GRADE – containing as much as possible iron oxide

2. COMPACTABILITY – not too compact or too brittle

3. PURITY – containing as less as possible impurities

4. SIMILARITY – containing similar composition to one another

2.3 Iron Production Process

Blast Furnace

1. It’s divided into 2 parts :

i. combustion chamber/ stove where the hot air from, blast into

the furnace

ii. fire bricks (furnace) to form a wide space (shaft) to

accommodate and discharge the heat

Types Characteristic

Magnetite Irons containing 72.4% irons, has magnetic properties and black

in colours.

Carbonate Irons containing less than 30% irons, others are carbon and

phosphorus.

Hematite Irons containing 40% - 65% irons and dark brown reddish in

colours and sometimes added with magnetite sulphade.

Limonite Irons containing 20% - 55% irons and 40% water, yellow

brownish in colours.

Pyrite Irons containing 50% irons and 50% sulphur, gold in colours

and found in crystalline structure.

Taconite Irons containing only 25% to 30% irons, reddish or blackish in

colours.

Sulphate Irons containing 50% sulphur, gold in colours and has few types

such as Phyrito Pyrite, Marcasite and Phynorite

Silicate Irons containing 50% silicon and divided into a few types such

as Kamosite, Stillprunite, Gururite and Minnesotite.

Siderite Irons containing 30% iron, yellow brownish in colours.

Part Function

Top The outside wall made by heat-proof material and the inside

wall covered with heat-proof ceramic

Supporting Part hearth – coated with carbon

bosh

stack - coated with aluminium silica

Pipe Channel waste gas pipe - to expel used gases

tuyere - to channeled hot air into the furnace

taphole - to expelled hot melt metal

slag taphole - to expelled slags

Melting process:

Raw materials (coke, pellet, sintered ore, iron ore, limestone)

solid raw materials used in this furnace and carried by a skip

car to the top of the furnace

1. tuyere made by brass and cooled with water

2. hot air blast stove used to heat the air up to 1100C

3. the air cooled and the used hot gases will flow repeatedly to the

opposite way from each other through the furnace

4. with the help of hot gases, the bricks lining will become hot and

will expelled heat to reheat the cooled air and it’s called

regeneration

5. the hot metal produced from the furnace every 2 hours

6. clays used to shut the hole will be drilled and after all the works

done, it will be shut back using clay gun

Chemical reaction in iron production from the blast furnace :

Iron ores + cokes + limestones + air slags + gases

3 important chemical processes in the blast furnace :

i. carbon from the coke burning with oxygen in the air blast

ii. oxide reduction to the irons

iii. flushing the gauge and ashes from the iron ores using the

limestone

The disadvantages:

i. high in cost and capital for operation

ii. controlling iron composition are weak

iii. small furnace using coke are uncompetant, huge production

from bigger furnace are no necessity.

The output (products) of the blast furnace :

i. the iron ingots contains 93% of basic irons, 3% - 5% of carbon,

silica, sulphur, phosphorus and manganese.

ii. besides, slags also can be used when separated from melting

irons in the furnace such as road ways and building blocks

2.4 Steel Production

Basic Oxygen Process Furnace (BOP)

Using pure oxygen.

Basic oxygen process operation :

1. It can move horizontally and vertically

2. Melting metals and 30% scraps was charging into the furnace

before it changed into vertical position

3. High speed oxygen was blow in directly to the melting metal surface

as shown in figure 3. The oxygen was cooled with water

4. Half of the carbon in the materials changes into oxide in gases form

which then expelled from the furnace through its own channel

5. Other impurities also became oxide and then react with limestones

to form slags

6. The furnace was leaned to horizontal position to discharge melting

steels and then change into inverted position to disposed the slags

as shown in figures 4, 5 and 6

Basic oxygen process outputs :

1. It can produce high quality steel faster with 80 tones per hour

2. The melting steel usually used to make steel ingots

Electric Arc Furnace

This furnace has high ability in production and easier to handle.

Low in oxygen rates made it suitable in producing steel alloy

because the metal did not react with the oxygen in the furnace.

This furnace used widely and suitable for upgrading the steel,

produces tool steel and high quality alloy steel without using

charging materials.

It can produce upto 120 tones of steels within 4 hours.

Fig 1 Fig 3 Fig 2

Fig 4 Fig 5 Fig 6

Electric Arc Furnace operation

1. Charging

Charge materials which containing steel scraps, iron ores, oxide irons

and limestones were added into the furnace.

Electric current flow to the carbon electrode to supply the electric arc.

2. Melting

The electric arc will melted the oxidize charge materials.

Silicon, manganese and phosphorus will start to oxidize and combined

with limestones to form slags.

Only the carbon electrodes are burning, therefore there is no metal

lost.

3. Slagging

The limestones, fluorspars and oxide irons are added to form slags.

After the reaction, it will form the needed steel compositions.

Sulphur then added to the slags as calcium sulphade.

The reaction are shown as below :

FeS + CaO + C CaS + Fe + CO

4. Finishing or tapping

The steel oxidized by aluminium, ferro-silicon or ferro-manganese to

retracted the steels.

Slags will be plucked or poured start from its surface and then will be

separated or tapped through a hole/ exit channel by leaning the

furnace.

The advantages of electric arc furnace :

i. blazing process can be controlled and arranged efficiently

ii. no oxidation gases, so can produce high quality steels

iii. the temperature can be control accurately

iv. free from soils and smokes

Fig 24 : Melting process

2.5 Plain Carbon Steel

Plain carbon steel is an iron carbon alloy containing 0.02 to 2%

carbon. All commercial plain carbon steels contains manganese,

sulphur, phosphorus and silicon impurities.

2.5.1 Iron-Carbon Phase Equilibrium Diagram

1. The Iron-Carbon Phase Diagram are a phase diagram that shows

the connection between amount of carbon and the changes of

internal structure by irons and steels while heated until reaching

their melting point.

2. Only ferrous metals could show the changes while it is heated.

3. First stage/ phase called lower critical temperature and the second

stage of changes called upper critical temperature.

4. The levels of lower critical temperature for every eutectoid steels

(0.8% carbon) are the same which it is about 723°C.

5. However, the upper critical temperatures are different depends on

the amount of carbon. The higher the amount (more than 0.8%),

the higher the temperature.

2.5.1.1 Irons, Steels and Cast Irons in the Iron-Carbon Phase

Equilibrium Diagram

1. Between the temperature of 1400C and 1537C, the solid irons

exist in body-centered cubic (BCC) and called as pearlite.

2. The temperature between 910C and 1400C, the crystalline

structures are face-centered cubic (FCC) called austenite.

3. The temperature 910C and below, the iron structures are body–

centered cubic (BCC) called ferrite.

4. At 1125C, cementite dissolvability in austenite irons is limited at

2% carbon only.

5. Cementite solid solutions in austenite called ferrite.

6. Eutectoid composition for ferrite and cementite called pearlite

which containing a lamellar structure consisting of alternate layers

of cementite and ferrite.

7. Ferrite and cementite only transformed from austenite with slow

cooling process. But with fast cooling process, the martensite will

transformed from austenite.

steel cast iron

Fig 1: Iron-Carbon Phase Equilibrium Diagram

liquid

1.0 2.0 3.0 4.0 5.0

700

900

1100

1300

1500

500

+ Fe3C

liquid +

+

+ Fe3C

(pearlite)

liquid + Fe3C

+

liquid +

Led

ebu

rite

oC

% C 0

2.6 Terminologies in Phase Diagram

1. Ferrite / (alpha-iron)

Ferrite is very soft, ductile and of relatively low strength

2. Austenite / (gamma iron)

Austenite is also a soft and ductile phase but stronger and less ductile

than ferrite

3. Cementite / Fe3C (iron carbide)

It is combinations of carbon with iron (Fe) to form iron carbide (Fe3C)

Cementite is a hard and brittle compound

4. Pearlite / + Fe3C

A lamellar structure consisting of alternate layers of ferrite and

cementite

A pearlite has a variable hardness

5. Martensite

The fast cooling of steel from austenite phase results in the formation

of a martensite

Hard and brittle

6. Ledeburite

Consisting of a mixture of two phases, austenite and cementite.

7. Lower Critical Temperature

It is the temperature, during heating, at which pearlite changes to

austenite. This transformation occurs at a fixed temperature of 723C

irrespective of the composition of the alloy

8. Upper Critical Temperature

It is the temperature, during heating, at which last traces of cementite

change into austenite and the alloy becomes completely austenite and

it varies from 723C to 1148C depending upon the carbon content in

the alloy

Fig 2: Microstructure for various phase of steel

Ferrite

Austenite

Cementite

Pearlite

Martensite

2.7 Types of Carbon Steels

Types Characteristic

Low carbon steel Contains less than 0.3% carbon (<0.3% C)

Low strength, good machinability, high ductility,

formability and weldability

Applications : bridge structures, buildings, ships, vehicles,

nails, rivets

Good fabrication ductility characteristic and usually used

in annealing and normalizing conditions

Medium carbon steel Contains 0.3 – 0.8% carbon

High strength and ductility after heat treatment, stability,

tough and tensile strength

Applications : railways, wheels, shafts, gears, bolts

It can be quenched to form martensite and bainite if using

media for quenching such as water and brine

High carbon steel Contains more than 0.8% carbon (>0.8% C)

Low in strength, high in hardness and wear resistance

after heat treatment

Applications : moulds, hammers, knives, milling cutters

Also known as tool steel

Tempering process can accelerate martensite formation

and maintain the low strength properties

2.8 Alloy Steels

1. Alloy steel may be defined as carbon steel to which one or more

elements are added to get some beneficial effects.

2. Main purposes :

i. to improve the quality of steels

ii. to improve steel characteristics

iii. to make it suitable for engineering works

iv. to make it easier for heat treatment process

3. The commonly added elements to achieve these properties :

i. increase tensile strength

ii. increase hardness and toughness

iii. higher hardenability

iv. changeability for critical temperature

v. increase wear and abrasive resistance

vi. higher corrosion and oxidation resistance

vii. maintaining higher hardness (red hardness) at temperatures

up to 600C, due to the presence of alloy carbides

viii. higher temperability, and maintain the hardness and strength

at elevated temperatures (creep strength)

2.8.1 Alloying elements and the effects

Nickel increase the strength, hardness and toughness

increase the machineability in finishing process

improves the corrosion resistance of steels

Chromium increase the strength and hardness

machineability

Manganese increase hardness and machineability

act as oxidation agent at higher temperature

high finishability

Silicon deoxidizer, fixing oxidation resistance at high

temperature increase the critical temperature for

heat treatment

Molybdenum easier for hardnessability

increase the tensile strength and creep at higher

temperature

Vanadium deoxidation, promotes the fine grain formation

Cuprum gives resistance to corrosion and act as strengthened

agent

Aluminium deoxidation, promotes the fine grain formation and

formed as nitriding steel

Boron increase the hardenability properties

Plumbum repairing the machineability properties

Bismuth repairing the machineability properties

2.8.2 Main Classes, Element Contents and Alloy Steels

Applications

Stainless steel Contains at least 12% chromium.

Chromium or nickel forms an oxide layer which protects the

underlying steel alloy from corroding.

App:

Tool steel Contains 0.6-1.5% carbon

High hardenability, Wear and corrosion resistance, Cannot

be reshaping, Require high toughness and resistance to

shock.

App:

Structural steel Contents : nickel, manganese, chromium, molybdenum.

High strength ,toughness, resistance to softening at elevated

temperatures, resistance to corrosion, good weldability,

workability , high hardenability.

App:

Magnetic steel Form in 2 methods :

Hard magnet – used to produce permanent magnet

Soft magnet – use to produce impermanent magnet

Heat resistance

steel

Contains chromium, nickel, silicon and manganese, others

are carbon and bismuth (30% carbon, 3.5% bismuth).

High resistance to corrosion and oxidation.

High in hardness and used for high temperature cutting.

2.9 Cast Irons

1. An alloy of iron and carbon containing 2 – 4% carbon.

2. Carbon content form in two ways:

a) cementite (Fe3C)

b) graphite (Fe+C) as free carbon when the cementite is

decomposed

2.9.1 Factors In Carbon Forming

Cooling / Solidifying Process Rate

The cooling rate depends on the thickness and type of die/mould.

1. Slow cooling : caused the carbon separated as graphite,

producing grey cast iron

2. Rapid cooling : prevent the change of graphite and maintain it

hardness and difficult to machined, producing white cast iron

Heat Treatment

1. With long heating process, white cast iron will be forming

graphite structure and are used to produce malleable steel.

High Carbon Contents

1. With high carbon contents, the cast irons will have the

tendency to solidify as grey cast irons.

2. The strength and hardness of irons increased with the

increasing of carbon.

Alloying Elements

Silicon - The higher silicon contents, causing higher resistance and

good magnetic properties

Sulphur - Causing the cast irons to be harden, embrittle and weak

Phosphorus - Increasing strength, hardness and improving the

resistance of corrosion

Manganese - Causing strength, toughness and high wear resistance,

hard to machine because of the hardness

2.9.2 Structures, Properties and the Usages of Cast Irons

Grey cast iron Present in the form of graphite flakes,

and shows a grey surface on the fracture.

Properties : easy to machine, good wear

resistance, high compressive strength

(140 -415 MPa)

Applications : gear boxes, base plates,

bearing brackets

White cast iron Present in the form of cementite, it is

called white cast iron because it shows a

white fractured surface.

Properties : brittle, low in impact

resistance, low in shock resistance

Applications : wearing plates, pump

liners, grinding balls

Malleable cast iron White cast irons heat treated to produce

castings which are bendable or malleable,

increase ductility.

The heat treatment will : increase tensile

strength, improve the ductility, improve

the malleability.

Applications : automobiles (steering

brackets, support brackets, shafts

brackets, camshafts), agricultural

machineries (tractors), machine tools and

electrical industries.

Nodular cast iron Contains large amounts of carbon in the

form of graphite nodules (spheres).

Properties : high strength, high toughness

and ductility, can be welded and

machined.

Applications : automotive parts (piston,

crankshafts, gears), dies (punch dies,

sheet metal dies).

2.10 The Advantages of Cast Irons

1. Widely used in industries as for :

i. cheaper and machineable

ii. low melting point (1140 - 1200oC) compared to steels

iii. liquidity and formability in casting

iv. wear resistance and moistureability