i c diagram

8/19/2019 I C Diagram

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Prepared by

Prof. Naman M. Dave

Assistant Professor,

Mechanical Engg. Dept.

Gandhinagar Institute of Technology.

MATERIAL SCIENCE &

METALLURGY

2131904


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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.


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• 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-Fe3Cdiagram.

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


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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


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1539

1404

910

768

( O C )

CURIE TEMP.

a = 2.93 AO

a = 3.63 AO

a = 2.87 AO

(FERRITE)

(AUSTENITE)

Prof. Naman M. Dave


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• Austenite γ

• Ferrite α

• Pearlite

• Cementite

Fe3C• Ledeburite

Iron

Carbon

Diagram

Prof. Naman M. Dave


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Eutectic Reaction in

Iron Carbon

Diagram

Prof. Naman M. Dave


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Eutectoid ReactionPeritectic Reaction


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Imp. Points /

Drawing

Technique1. 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 ImpMicro-strs.

7. Mark 7 Mixedphases

8. Mark 8 Imp.Temps

9. Mark 8 impcurves

10. Mark 9 Imp.C% & different

types of

ferrous alloys

Solidus

0.008%

Iron Carbon

Diagram


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Ferrite (Light) + Cementite (Dark)

orFe3C

or

Pearlite

Austenite + Cementite

orγ Fe3C

or

Ledeburite

Micro-str. of various phases of Fe-C dig

Prof. Naman M. Dave


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Micro-str. of various phases

Solid Phases


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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 °CAverage 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°CProf. Naman M. Dave


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3.4 Micro-str. of various phases of Fe-C dig.

Prof. Naman M. Dave


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Tie-Line at the room temp.

Amount of ferrite & perlite

%5.49792.0

392.0

008.080.0

008.040.0

pearlite f %5.50792.0

40.0

008.080.0

40.080.0

ferrite f

f a

f p

0.4

0.008 0.8

By Applying Lever

Rule

Prof. Naman M. Dave


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Prof. Naman M. Dave


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https://www.youtube.com/watch?v=NLLpn7ZEWNY

https://www.youtube.com/watch?v=NLLpn7ZEWNYhttps://www.youtube.com/watch?v=NLLpn7ZEWNY


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(1) Cooling of 0.38% C (Hypo-eutectoid) Steel

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Microstructure of Hypoeutectoid steel (II)

Hypoeutectoid alloys

contain proeutectoid

ferrite (formed above

the eutectoid

temperature) plus theeutectoid perlite that

contain eutectoid

ferrite and cementite.


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(2) Cooling of 0.8% C (Eutectoid) Steel

Prof. Naman M. Dave


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(3) Cooling of 1.4% C (Hyper-eutectoid) Steel

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Microstructure of hypereutectoid steel (II)

Hypereutectoid alloys contain

proeutectoid cementite

(formed above the eutectoid

temperature) plus perlite that

contain eutectoid ferrite and

cementite.


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Micro-Str. Of Plain Carbon Steels

Medium Carbon Steel (0.3-0.6%C)

High Carbon Steel (0.6-1.4%C)

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i c diagram

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