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Draw Iron carbon phase equilibrium diagram; identify phases of steels and cast iron on diagram to interpret their significance.
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2. Pure metal
A pure metal is a substance that contains atoms of only one type of metallic element, such as aluminum, gold, copper, lead or zinc.
Alloy
An alloy is a material composed of two or more metals or a metal and a nonmetal.
Phase
a phase is a region of space , throughout which all physical properties of a material are essentially uniform.
In a system consisting of ice and water in a glass jar, the ice cubes are one phase, the water is a second phase, and the humid air over the water is a third phase. The glass of the jar is another separate phase

3. Solid solubility
The degree to which one solid component can dissolve another. or
The extent to which one metal is capable of forming solid solutions with another.

4. Solid Solutions 4

5. Solid Solutions 5

6. Iron changes its crystal structure from BCC to
Allotropy of Iron
Iron changes its crystal structure from BCC to
FCC at 910 c , then again to BCC at 1400 c and further heating , it melts at 1539 c . This change of crystal structure Is called allotropy.

7. Temp
1539 0C
14000C
910 0C
Time

8. Allotropy of Iron
1539
1400
910
768

9. α-ferrite Phases in Steel
Interstitial solid solution of carbon dissolve in α-iron having BCC structure.
Maximum solubility of carbon in α-iron is 0.02% (at 7270C)
At room temperature solubility is 0.008%

10. Phases in Steel 0.025 wt% C   Fe3C (cementite) L T(°C)  +L
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L 
(austenite)  +L
+ Fe3C 
L+Fe3C 
Co , wt% C
1148°C
T(°C)
727°C R S
CFe C 3 C

11. Properties of α-ferrite
Phases in Steel
Properties of α-ferrite
Soft and ductile phase
Ferromagnetic upto temperature(7680C)
Tensile Strength
40,000psi
Elongation
40% (2in GL)
Hardness
80 BHN
Toughness
Low

12. Microstructure of α-ferrite
Phases in Steel
Microstructure of α-ferrite

13. Austenite (γ) Phases in Steel
Interstitial solid solution of carbon dissolve in γ-iron having FCC structure.
Maximum solubility of carbon in γ-iron is 2% (at 11470C)
Stable only above 7270C

14. Phases in Steel CO = 2 wt% C   Fe3C (cementite) L T(°C)  +L
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L 
(austenite)  +L
+ Fe3C 
L+Fe3C 
Co , wt% C
1147°C
T(°C)
727°C S

15. Properties of Austenite
Phases in Steel
Properties of Austenite
Soft and ductile phase
Non magnetic
Tensile Strength
1,50,000psi
Elongation
10%
Hardness
Rc 40
Toughness
High

16. Microstructure of Austenite
Phases in Steel
Microstructure of Austenite

17. δ-ferrite Phases in Steel
Interstitial solid solution of carbon dissolve in δ-iron having BCC structure.
Maximum solubility of carbon in δ-iron is 0.1% (at 14920C)
Stable only above 14000C

18. Phases in Steel CO = 0.1 wt% C  1492  Fe3C (cementite) L T(°C)  +L
1600
1400
1200
1000
800
600
400 1 2 3 4 5 6
6.7 L 
(austenite)  +L
+ Fe3C 
L+Fe3C 
Co , wt% C
1147°C
T(°C)
727°C
1492 S

19. Iron Carbide (Cementite)
Phases in Steel
Iron Carbide (Cementite)
compound of iron and carbon with fixed carbon content of 6.67% and having orthorhombic structure.
Chemical formula Fe3C

20. Properties of Iron Carbide (Cementite)
Phases in Steel
Properties of Iron Carbide (Cementite)
Extremely hard and brittle phase
Ferromagnetic upto 2100C
Tensile Strength
5000psi
Elongation 1%
Hardness
VHN
Toughness
Very Low
Compressive Strength
Very High

21. Transformations Peritectic reaction: S1 + L S2 Eutectic reaction:
L S1 + S2
Eutectoid reaction:
S S2 + S3
9-5

22. Transformations Peritectic reaction: S1 + L S2 General Reaction:
Reaction in steel:
Liquid δ γ
0.55%C % C % C
BCC FCC
14920C
Cooling
9-5

23. Iron-Carbon System
c10f28

24. Transformations Eutectic reaction: L S1 + S2 General Reaction:
Reaction in steel:
Liquid γ Fe3C
4.3%C % C % C
FCC Orthorhom
11470C
Cooling
9-5

25. Iron-Carbon System
c10f28

26. Transformations Eutectoid reaction: S1 S2 + S3 General Reaction:
Reaction in steel:
γ α Fe3C
0.8%C % C % C
FCC BCC Orthorhombic
7270C
Cooling
9-5

27. Eutectoid reaction: γ α + Fe3C 7270C 0.8%C 0.02% C 6.67% C
FCC BCC Orthorhombic
This eutectoid mixture is called Pearlite due to its pearly appearance under microscope.
Pearlite: It is a eutectoid mixture of alpha ferrite
and cementite formed from austenite containing
0.8%C while cooling at 7270C
7270C
Cooling
9-5

28. Iron-Carbon System
c10f28

29. Properties of Pearlite
Phases in Steel
Properties of Pearlite
Good Hardness and T.S.
magnetic
Tensile Strength
1,20,000psi
Elongation
20% (2in GL)
Hardness
Rc 20 (250 BHN)
Toughness
High

31. Why Solubility of Carbon in Austenite is Very High?
α-ferrite
BCC 31

32. Why Solubility of Carbon in Austenite is Very High?
FCC 32

33. Classification of Steels
Steels are classified base on various criterions:
Amount of carbon
Amount of alloying elements
Amount of deoxidation
Grain Coasening Characteristics
Method of Manufacturing
Depth of Hardening
Form and use 33

34. Classification of Steels
Amount of carbon
Low carbon steel
(0.008 – 0.3 %C)
Medium carbon steel
(0.3 – 0.6 %C)
High carbon steel
(0.6 – 2 %C) 34

35. Classification of Steels
On the basis of alloying elements
Low alloy steels
(Total alloying elements are less than 10%)
High alloy steels
(Total alloying elements are more than 10%) 35

36. Classification of Steels
On the basis of alloying elements and carbon content
Low carbon Low alloy steels
Low carbon High alloy steels
Medium carbon Low alloy steels
Medium carbon High alloy steels
High carbon Low alloy steels
High carbon High alloy steels 36

37. Classification of Steels
On the basis of form and us
Based on form:
Cast steels
Wrought steels
Based on Use:
Boiler steels
Case hardening steels
Corrosion and heat resistant steels
Deep drawing steels
Electrical steels
Free Cutting steels
Machinery steels
Structural steels
Tool steels 37

38. Specification of Steels
Steels are specified on the basis of criteria like:
Chemical Composition
Mechanical Properties
Method of manufacturing
Heat Treatment
Quality
Majority of specifications are based on chemical composition. 38

39. Iron-Carbon System
c10f28

40. Cooling curve of pure metal
Liquid metal cools from P to Q. Crystal begin to form at Q. Between Q and R the mass is partly liquid and partly solid. From R to S metal solidifies. Temperature remains constant from Q o R.

41. Cooling curve for binary solid solution
Here temperature does not remain constant but drop along the line QR.

42. Cooling curve for binary eutectic system
In this system , the two components are completely soluble in liquid state but entirely in soluble in in solid state. At point Q one component that is in excess will crystallize and temperature will drop along QR. at point R, two components crystallize simultaneously from solution
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