chapter 2 jf302
TRANSCRIPT
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JF302 –
MATERIALS
TECHNOLOGY 1
CHAPTER 3
FERROUS MATERIAL STRUCTURE &
BINARY ALLOY SYSTEM
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Understand metal production – iron and steel
Understand the process of iron and steel production
Understand plain carbon
Understanf alloy steel
Understand cast iron
LEARNING OUTLINE
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IRON
Iron is an element and can be pure.
Iron can be extracted from iron ores such as rocks, mineral.
The extracted process can be done through Blast Furnace.
Basic constituent of steel.
Iron ores content: -
Magnetite
Iron Carbonate
Hematite
Limonite
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Chemical Formula is (Fe 3O4).
Also called as Black Iron Ore - because the colour is black.
Percentage of Iron; 72 – 62% Fe (Iron)
MAGNETITE
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Also know as sindrite
Chemical formula (FeCO3)
Its color is yellowish green
Percentage of iron; 35 – 40% Fe (Iron)
IRON CARBONATE
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Chemical formula (Fe2O3)
Also known as Red Iron Ore.
Percentage of Iron; 70% Fe (Iron).
HEMATITE
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Chemical formula is (FeO(OH).n(H2O))
Also known as Brown Iron Ore
LIMONITE
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The purpose of use blast furnace is to reduce and convert iron
oxides into liquid iron called “hot metal”.
The appearance of blast furnace is huge, steel stack lined
with refractory brick.
Iron ores, coke and limestone are put into the top and
preheated air blown into the bottom.
Iron can be extracted by blast furnace because it can be
displaced by carbon.
It more efficient and more cost effective.
BLAST FURNACE
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BLAST FURNACE
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To ensure the process of extraction there are combined
mixture of subtances needed and called as charge.
Charge:
Iron ore, haematite - often contains sand with iron oxide, Fe2O3.
Limestone (calcium carbonate).
Coke - mainly carbon
The charge is placed a giant chimney called a blast furnace.
The blast furnace is around 30 metres high and lined with
fireproof bricks. Hot air is blasted through the bottom.
THE PROCESS OF BLAST FURNACE
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Oxygen in the air reacts with coke to give carbon dioxide:
C(s) + O 2(g) CO2(g)
The limestone breaks down to form carbon dioxide :
CaCO3(s) CO2 (g) + CaO(s)
Carbon dioxide produced in 1 + 2 react with more coke to produce carbon monoxide:
CO2(g)
+ C(s)
2CO(g)
The carbon monoxide reduces the iron in the ore to give molten iron :
3CO(g)
+ Fe2O
3(s) 2Fe
(l) + 3CO
2(g)
The limestone from 2, reacts with the sand to form slag (calcium silicate ):
CaO (s) + SiO (s) CaSiO3(l)
REACTION OF IRON PRODUCTION
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Both the slag and iron are drained from the bottom of the
furnace.
• The slag is mainly used to build roads.
• The iron whilst molten is poured into moulds and left to
solidify - this is called cast iron and is used to make railings
and storage tanks.
• The rest of the iron is used to make steel.
REACTION OF IRON PRODUCTION
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It’s included in the term ferrous metal
It’s a combination of iron & carbon( 0.01 – 1%)
Contains varying amounts of manganese, phosphorus, sulfur,
silicon & 20 other alloys
Alloys added to produce steel of dif ferent characteristics .
To produce useful steel, pig iron need to be oxidized in
another furnace at about 1650°C.
Molten iron is not useful because it’s weak and brittle
although it’s very hard .
STEEL
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Fastest steelmaking process – can make 250 tons of steel / hour
Melted molten iron and scrap are poured (charged) into a vessel.
Fluxing agents are added, like limestone.
The molten metal is blasted with pure oxygen. This produces iron oxide which then reacts with carbon to produce CO and CO2. The slag floats to the top of the metal.
Higher steel quality than open hearth. Used to make plate, sheet, I -beam, tubing and channel.
BASIC OXYGEN FURNACE
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ELECTRIC FURNACE
Uses electric arc from electrode to metal to heat and melt it.
Can produce 60-90 tons of steel per day.
Steel is higher quality than open-hearth and BOF
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IRON – CARBON PHASE DIAGRAM
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PHASE IN FE-C PHASE DIAGRAM
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The following phases are involved in the transformation, occurring with
iron-carbon alloys:
L - Liquid solution of carbon in iron;
δ-ferrite – Solid solution of carbon in iron.
Austenite – interstitial solid solution of carbon in γ -iron.
α-ferrite – solid solution of carbon in α-iron
Cementite – iron carbide, intermetallic compound, having fixed
composition Fe3C.
PHASE IN TRANSFORMATION OF IRON –
CARBON ALLOY
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Maximum concentration of carbon in δ-ferrite is 0.09% at 2719 ºF (1493ºC) – temperature of the peritectic transformation.
The crystal structure of δ-ferrite is BCC (cubic body centered).
FERRITE
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Austenite has FCC (cubic face centered) crystal structure, permitting high solubility of carbon – up to 2.06% at 2097 ºF (1147 ºC).
Austenite does not exist below 1333 ºF (723ºC) and maximum carbon concentration at this temperature is 0.83%.
Solubility is higher when compared to ferrite.
AUSTENITE
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α-ferrite has BCC
crystal structure
low solubility of
carbon – up to
0.025% at 1333 ºF
(723ºC).
α-ferrite exists at
room temperature.
FERRITE
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It is an intermetallic
compound
Cementite is a hard and
brittle substance,
influencing on the
properties of steels and cast
irons.
Low tensile strenght and
high comprehensive
strength.
Crystal structure is
orthormobic.
CEMENTITE
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T h e f o l l o w i n g p h a s e t r a n s f o r m a t i o n s o c c u r w i t h i r o n - c a r bo n a l l o y s :
A l l o y s , c o n t a i n i n g u p t o 0 . 5 1 % o f c a r b o n , s t a r t s o l i d i f i c a t i o n w i t h f o r m a t i o n o f c r y s t a l s o f δ - f e r r i t e .
C a r b o n c o n t e n t i n δ - f e r r i t e i n c r e a s e s u p t o 0 . 0 9 % i n c o u r s e s o l i d i f i c a t i o n , a n d a t 2 7 1 9 º F ( 1 4 9 3 º C )
r e m a i n i n g l i q u i d p h a s e a n d δ - f e r r i t e p e r f o r m p e r i t e c t i c t r a n s f o r m a t i o n , r e s u l t i n g i n f o r m a t i o n o f
a u s t e n i t e .
A l l o y s , c o n t a i n i n g c a r b o n m o r e t h a n 0 . 5 1 % , b u t l e s s t h a n 2 . 0 6 % , f o r m p r i m a r y a u s t e n i t e c r y s t a l s i n
t h e b e g i n n i n g o f s o l i d i f i c a t i o n a n d w h e n t h e t e m p e r a t u r e r e a c h e s t h e c u r v e A C M p r i m a r y c e m e n t i t e
s t a r s t o f o r m .
I r o n - c a r bo n a l l o y s , c o n t a i n i n g u p t o 2 . 0 6 % o f c a r b o n , a r e c a l l e d s t e e l s .
A l l o y s , c o n t a i n i n g f r o m 2 . 0 6 t o 6 . 6 7 % o f c a r b o n , e x p e r i e n c e e u t e c t i c t r a n s f o r m a t i o n a t 2 0 9 7 º F
( 1 1 4 7 º C ) . T h e e u t e c t i c c o n c e n t r a t i o n o f c a r b o n i s 4 . 3 % .
I n p r a c t i c e o n l y h y p o e u te c t i c a l l o y s a r e u s e d . T h e s e a l l o y s ( c a r b o n c o n t e n t f r o m 2 . 0 6 % t o 4 . 3 % ) a r e
c a l l e d c a s t i r o n s . W h e n t e m p e r a t u r e o f a n a l l o y f r o m t h i s r a n g e r e a c h e s 2 0 9 7 º F ( 1 1 4 7 º C ) , i t
c o n t a i n s p r i m a r y a u s t e n i t e c r y s ta l s a n d s o m e a m o u n t o f t h e l i q u i d p h a s e . T h e l a t t e r d e c o m p o s e s b y
e u t e c t i c m e c h a n i s m t o a f i n e m i x t u re o f a u s t e n i t e a n d c e m e n t i t e , c a l l e d l e d e b u r i t e .
A l l i r o n - c a r bo n a l l o y s ( s t e e l s a n d c a s t i r o n s ) e x p e r i e n c e e u t e c t o i d t r a n s f o r m a t i o n a t 1 3 3 3 º F
( 7 2 3 º C ) . T h e e u t e c t o i d c o n c e n t ra t i o n o f c a r b o n i s 0 . 8 3 % .
W h e n t h e t e m p e r a t u re o f a n a l l o y r e a c h e s 1 3 3 3 º F ( 7 3 3 º C ) , a u s t e n i t e t r a n s f o r m s t o p e a r l i t e ( f i n e
f e r r i t e - c e m e n t i t e s t r u c t u re , f o r m i n g a s a r e s u l t o f d e c o m p o s i t i o n o f a u s t e n i t e a t s l o w c o o l i n g
c o n d i t i o n s ) .
PHASE TRANSFORMATIONS OCCUR WITH
IRON - CARBON ALLOYS
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Classification. Three types of ferrous alloys :
Iron: less than 0.008 wt % C in α−ferrite at room T
Steels: 0.008 - 2.14 wt % C (usually < 1 wt % ) α-ferrite + Fe3C at
room T (Chapter 12)
Cast iron: 2.14 - 6.7 wt % (usually < 4.5 wt %)
TYPES OF FERROUS ALLOYS
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Critical temperatures
Upper critical temperature (point) A3 is the temperature,
below which ferrite starts to form as a result of ejection from
austenite in the hypoeutectoid alloys.
Upper critical temperature (point) ACM is the temperature,
below which cementite starts to form as a result of ejection
from austenite in the hypereutectoid alloys.
Lower critical temperature (point) A1 is the temperature of
the austenite-to-pearlite eutectoid transformation. Below this
temperature austenite does not exist.
Magnetic transformation temperature A2 is the temperature
below which α -ferrite is ferromagnetic.
CRITICAL TEMPERATURES
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TO BE CONTINUED
NEXT CLASS
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Alloy steels are iron-carbon alloys, to which alloying elements
are added with a purpose to improve the steels properties as
compared to the carbon steels.
Purpose of alloying
Increase hardenability
Improve strength at ordinary temperature
Improve mechanical properties at either high or low temperatures
Improve toughness at any minimum hardness or strength
Increase wear resistance
Increase corrosion resistance
Improve magnetic properties
ALLOY STEELS