iron carbon diagram
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Prepared by
Prof. Naman M. Dave
Assistant Professor,
Mechanical Engg. Dept.
Gandhinagar Institute of Technology.
MATERIAL SCIENCE &
METALLURGY
2131904
Please do not blindly follow
the presentation files only, refer
it just as reference material.
More concentration should
on class room work and text
book-reference books.
• In an almost pure form, known as Ingot or Wrought Iron, Iron has limited
applications like roofing, ducts, drainage culverts and as a base enamel in
refrigerator cabinets, stoves, washing machines, etc.
• In an alloyed form, Carbon is mixed with Iron to form alloys. Alloys of the
Iron-Carbon system are known as Ferrous Alloys. They include Plain Carbon
Steels, Alloy Steels and Cast Iron.
• The metal Iron is a primary constituent of some of the most important
engineering alloys and hence it is important to study the Iron-Carbon Diagram.
• Iron – Carbon Diagram is also known as Iron – Carbon Phase Diagram or Iron
– Carbon Equilibrium diagram or Iron – Iron Carbide diagram or Fe-Fe3C
diagram.
Carbon % Form of material
Below 0.08 Ingot or Wrought Iron
0.08 to 2.1% PCS or CS.
0.08 to 2.1% + some other
elements (like Cr, V, Mo, etc.
Alloy Steel.
2.1 to 6.67% CI.
Above 6.67% Pig Iron
Prof. Naman M. Dave
Polymorphism is a physical phenomenon where a material may have
more than one crystal structure i.e. its crystal structure may change
with change in temperature or external pressure or both.
If the change in structure is reversible, then the polymorphic change
is known as allotropy.
One familiar example is found in carbon: graphite is the stable
polymorph at ambient conditions, whereas diamond is formed at
extremely high pressures.
The best known example for allotropy is iron.
When iron crystallizes at 1539 C it is B.C.C. (δ-iron), at 1404 C the structure changes to
F.C.C. (γ-iron or austenite), and at 910 C it again becomes B.C.C. (α-iron or ferrite).
Prof. Naman M. Dave
1539
1404
910
768
(OC
)
CURIE TEMP.
a = 2.93 AO
a = 3.63 AO
a = 2.87 AO
(FERRITE)
(AUSTENITE)
Prof. Naman M. Dave
• Austenite γ
• Ferrite α
• Pearlite
• Cementite
Fe3C
• Ledeburite
Iron
Carbon
Diagram
Prof. Naman M. Dave
Eutectic Reaction in
Iron Carbon
Diagram
Prof. Naman M. Dave
Eutectoid Reaction Peritectic Reaction
Imp. Points / Drawing Technique
1. Draw a box 2. Mark %C on X &
temp on Y
3. Draw 3 hori.
lines & vert.lines & draw diagram
4. Mark 3 Imp.
Reaction pts.
5. Mark 5 pure
phases
6. Mark 5 Imp
Micro-strs.
7. Mark 7 Mixed
phases
8. Mark 8 Imp.
Temps
9. Mark 8 imp
curves
10. Mark 9 Imp.
C% & different types of ferrous alloys
Solidus
0.008%
Iron Carbon
Diagram
Ferrite (Light) + Cementite (Dark) or
a+Fe3C or
Pearlite
Austenite + Cementite or
γ +Fe3C or
Ledeburite
Micro-str. of various phases of Fe-C dig
Prof. Naman M. Dave
Micro-str. of various phases
Solid Phases
Phases in Fe–Fe3C Phase Diagram α-ferrite - solid solution of C in BCC Fe • Stable form of iron at room temperature. • The maximum solubility of C is 0.022 wt% • Transforms to FCC γ-austenite at 912 °C Average properties: 40,000 psi TS, 40 % elong. in 2 inch, < RC 0 or < RB 90 hardness. γ-austenite - solid solution of C in FCC Fe • The maximum solubility of C is 2.14 wt %. • Transforms to BCC δ-ferrite at 1395 °C • Is not stable below the eutectoid temperature (727 °C) unless cooled rapidly Average properties: 150,000 psi TS, 10 % elong. in 2 inch, RC 40 hardness, high toughness. δ-ferrite solid solution of C in BCC Fe • The same structure as a-ferrite • Stable only at high T, above 1394 °C • Melts at 1538 °C Fe3C (iron carbide or cementite) • This intermetallic compound is metastable, it remains as a compound indefinitely at room T, but decomposes (very slowly, within several years) into α-Fe and C (graphite) at 650 - 700°C
Prof. Naman M. Dave
3.4 Micro-str. of various phases of Fe-C dig.
Prof. Naman M. Dave
Tie-Line at the room temp.
Amount of ferrite & perlite
%5.49792.0
392.0
008.080.0
008.040.0
pearlitef%5.50
792.0
40.0
008.080.0
40.080.0
ferritef
f a f p 0.4
0.008 0.8
By Applying Lever
Rule
Prof. Naman M. Dave
3.4 Micro-str. of various phases of Fe-C dig.
Prof. Naman M. Dave
(1) Cooling of 0.38% C (Hypo-eutectoid) Steel
Prof. Naman M. Dave
Microstructure of Hypoeutectoid steel (II)
Hypoeutectoid alloys contain proeutectoid ferrite (formed above the eutectoid temperature) plus the eutectoid perlite that contain eutectoid ferrite and cementite.
(2) Cooling of 0.8% C (Eutectoid) Steel
Prof. Naman M. Dave
(3) Cooling of 1.4% C (Hyper-eutectoid) Steel
Prof. Naman M. Dave
Microstructure of hypereutectoid steel (II)
Hypereutectoid alloys contain proeutectoid cementite (formed above the eutectoid temperature) plus perlite that contain eutectoid ferrite and cementite.
3.4 Micro-str. of various phases of Fe-C dig. Micro-Str. Of Plain Carbon Steels
Medium Carbon Steel (0.3-0.6%C)
High Carbon Steel (0.6-1.4%C)
Prof. Naman M. Dave
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