Topic related to material science and metallurgy, Includes basic information about steel.Also the Iron-Iron Carbon Diagrams and its structures with various features of fe-c diagram.

1. Mechanical Engineering

2. STEEL
Sub:- Material Science & Metallurgy
Prepared By: -
Sagathiya Naisarg

3. STEEL
Steel is also produced from pig iron by
removing the impurities and by decreasing
the carbon content.
Pig iron is again heated and the excess
carbon is removed as CO2 gas and the
oxides of other impurities form a slag on top
of the molten steel.

4. Steel Production
• Ferrous metals are those metals that
contain Iron.
• The steel production process might be
divided into three phases:
• Reduction of iron to pig iron
• Refining pig iron to steel
• Forming the steel into products

5. Composition of Steel
• The essential difference between cast iron and
steel is in the amount of carbon contained in the
constituency of the metal.
• Steel is fundamentally an alloy of iron and carbon
with carbon content less than 1.5% while cast
iron is an alloy of iron and carbon with carbon
content ranging between 1.5 to 4% .

6. FACTORS THAT AFFECT
PROPERTIES OF STEELS
 Carbon content
 Heat treatment and shaping method
 Presence of harmful elements
 Presence of alloying materials.

7. Allotropic forms of iron
• Elements or compounde exist in more
than one crystalline form under different
conditions of temperature and pressure.
• This phenomenon is called allotropy or
polymorphism.
• Allotropy is characterised by a change
in atomic structure which occure at a
difinite transformation temperature.

8. Fe-C True Equilibrium
Diagram
8
A phase diagaram
shows us the
microstructure
within a material
as function of the
material
composition and
material
temperature
1600
1400
1200
1000
800
600
400
0 1 2 3 4 90
L
g +L
 + Graphite
Liquid +
Graphite
(Fe) Co, wt% C
0.65
740°C
T(°C)
g + Graphite
100
1153°Cg
Austenite 4.2 wt% C
 + g

9. IRON IRON-CARBON
DIAGRAM
Ferrite
Austenite
Steel Cast iron
Pearlite
Pearlite and
Cementine
Pearlite and
Carbide
Eutectic
eutectoid

10. Definition of structures
Various phases that appear on the Iron-
Carbon equilibrium phase diagram are
as under:
•Austenite
•Ferrite
•Pearlite
•Cementite
•Martensite*
•Ledeburite

11. Definition of structures
• Ferrite is known as α solid solution.
• It is an interstitial solid solution of a small
amount of carbon dissolved in α (BCC) iron.
• stable form of iron below 912 deg.C
• The maximum solubility is 0.025 % C at
723C and it dissolves only 0.008 % C at
room temperature.
• It is the softest structure that appears on the
diagram.

12. Definition of structures
• Pearlite is the eutectoid mixture
containing 0.80 % C and is
formed at 723°C on very slow
cooling.
• It is a very fine platelike or
lamellar mixture of ferrite and
cementite.
• The white ferritic background or
matrix contains thin plates of
cementite (dark).

13. Definition of structures
• Austenite is an interstitial solid solution of
Carbon dissolved in g (F.C.C.) iron.
• Maximum solubility is 2.0 % C at 1130°C.
• High formability, most of heat treatments
begin with this single phase.
• It is normally not stable at room
temperature. But, under certain conditions it
is possible to obtain austenite at room
temperature.

14. Definition of structures
• Cementite or iron carbide, is very hard,
brittle intermetallic compound of iron &
carbon, as Fe3C, contains 6.67 % C.
• It is the hardest structure that appears on the
diagram, exact melting point unknown.
• Its crystal structure is orthorhombic.
• It is has
• low tensile strength (approx. 5,000 psi),
but
• high compressive strength.

15. Definition of structures
 Martensite - a super-saturated solid solution of
carbon in ferrite.
It is formed when steel is cooled so rapidly that
the change from austenite to pearlite is
suppressed.
 The interstitial carbon atoms distort the BCC
ferrite into a BC-tetragonal structure (BCT).;
responsible for the hardness of quenched steel

16. Definition of structures
• Ledeburite is the eutectic mixture
of austenite and cementite.
• It contains 4.3 percent C and is
formed at 1130°C.

17. Various Features of Fe-C diagram
Peritectic L + d = g
Eutectic L = g + Fe3C
Eutectoid g =  + Fe3C
Phases present
L
Reactions
d
BCC structure
Paramagnetic
g austenite
FCC structure
Non-magnetic
ductile
 ferrite
BCC structure
Ferromagnetic
Fairly ductile
Fe3C cementite
Orthorhombic
Hard
brittle
Max. solubility of C in ferrite=0.022%
Max. solubility of C in austenite=2.11%

18. The Iron-Iron Carbide
DiagramThe diagram shows three horizontal lines which
indicate isothermal reactions (on cooling /
heating):
• First horizontal line is at 1490°C, where peritectic
reaction takes place:
Liquid + d ↔ austenite
• Second horizontal line is at 1130°C, where
eutectic reaction takes place:
liquid ↔ austenite + cementite
• Third horizontal line is at 723°C, where eutectoid
reaction takes place:
austenite ↔ pearlite (mixture of ferrite &
cementite)

19. The Iron-Iron Carbide Diagram
• A map of the temperature at which different
phase changes occur on very slow heating
and cooling in relation to Carbon, is called
Iron- Carbon Diagram.
• Iron- Carbon diagram shows
• the type of alloys formed under very slow
cooling,
• proper heat-treatment temperature and
• how the properties of steels and cast irons
can be radically changed by heat-treatment.

20. Three Phase Reactions
• Peritectic, at 1490 deg.C, with low wt% C
alloys (almost no engineering importance).
• Eutectic, at 1130 deg.C, with 4.3wt% C,
alloys called cast irons.
• Eutectoid, at 723 deg.C with eutectoid
composition of 0.8wt% C, two-phase mixture
(ferrite & cementite). They are steels.

21. References
1. ) Article of Properties of steel from
Wikipedia
2) Book Of Material Science and
Metallurgy By K. I. Parashivamurthy
3) Photos from Google.

22. THANKS