Fe-Fe 3C Equilibrium Phase Diagram

Fe-Fe3C Equilibrium Phase Diagram

Panya Buahombura School of Metallurgical Engineering Suranaree University of Technology School of Metallurgical Engineering, SUT

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Allotropic Transformation in Iron (Fe) 1536 oC 1400 oC

910 oC 760 oC

School of Metallurgical Engineering, SUT

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  กกก  (Fe-Fe3C equilibrium diagram) School of Metallurgical Engineering, (Materials Science and Metallurgy, 4th edition, Pollack,SUT Prentice-Hall, 1988.)

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Iron-Carbon Alloy System Fe-Fe3C Phase Diagram - Not a true equilibrium diagram - Fe3C is meta-stable phase (meta-stable condition) - Fe3C will decompose into Fe and C (graphite) but take very long time - Fe-Fe3C diagram consider as representing the equilibrium diagram School of Metallurgical Engineering, SUT

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α -Ferrite • Interstitial solid solution
ก

ก   

•      

0.025%  723 ºC ! " 0.008% 

• Body-Centered Cubic (BCC) crystal structure

• Tensile strength: 28 kg/mm2 • Elongation: 40%

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α-Ferrite

Microstructure of Ferrite Magnification: 100x

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δ-Ferrite • Interstitial solid solution
 กก   

•     δ-Ferrite   0.10%  1495 ºC • Body-Centered Cubic (BCC) crystal structure

• Stable at high temperature

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γ (Austenite) • Interstitial solid solution
ก

ก   

•    #  2.0%  1148 ºC • Face-Centered Cubic (FCC) crystal structure

• Not stable at room temperature

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γ (Austenite)

Microstructure of Austenite Magnification: 500x

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Fe3C (Cementite) • Iron carbide → Fe3C • Intermetallic compound • 6.67 %C • Orthorhombic crystal structure • Hard and brittle • Stable at room temperature

School of Metallurgical Engineering, SUT

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Pearlite (Eutectoid mixture) •
กกก   eutectoid   γ (0.80 %C)

ก α (0.025 %C) ก Fe3C (6.67 %C)

 723 ºC

• Lamellar mixture of α ferrite and Fe3C • Tensile strength: 80 kg/mm2 • Elongation: 20%

School of Metallurgical Engineering, SUT

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Pearlite (Eutectoid mixture)

2500X

17000X

Microstructure of Pearlite School of Metallurgical Engineering, SUT

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Ledeburite (Eutectic mixture) •
กกก   eutectic   Liquid (4.3 %C) ก γ (2.0 %C) ก

Fe3C (6.67 %C)  1148 ºC • Eutectic mixture of γ and Fe3C • Not stable at room temperature

School of Metallurgical Engineering, SUT

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$%ก  !&กก    (Reaction in Fe-Fe3C Phase Diagram)

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Peritectic Reaction (at 1495 ºC) Liquid (0.50%C) + δ (0.10%C) → γ (0.18%C)

Eutectic Reaction (at 1148 ºC) Liquid (4.30%C) → γ (2.00%C) + Fe3C (6.67%C)

Eutectoid Reaction (at 723 ºC) γ (0.80%C) → α (0.025%C) + Fe3C (6.67%C)

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Steel (%Carbon ≤ 2.0%) • Eutectoid Steel (0.8 %C) • Hypo-eutectoid steel (< 0.8 %C) • Hyper-eutectoid steel (0.8% < %C ≤ 2.0%)

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Cast Iron (%Carbon > 2.0%) • Hypo-eutectic cast iron (2.0% < %C < 4.3%) • Hyper-eutectic cast iron (4.3% < %C < 6.67%)

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+   
กก    (Structures of Carbon Steel)

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Eutectoid Steel $,กก    %C = 0.80% α Ferrite

+    Pearlite 100%

Fe3C School of Metallurgical Engineering, SUT

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Hypo-eutectoid Steel $,กก    %C < 0.80% α Ferrite

Pearlite

+    Ferrite + Pearlite School of Metallurgical Engineering, SUT

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Hypo-eutectoid Steel $,กก    %C < 0.80%

• Proeutectoid α • Eutectoid α

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Hyper-eutectoid Steel $,กก    %C > 0.80% !#.

≤ 2.0%

Fe3C

Pearlite

+    Pearlite + Fe3C School of Metallurgical Engineering, SUT

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Hyper-eutectoid Steel

$,กก    %C > 0.80% !#.

≤ 2.0%

Proeutectic Fe3C Eutectic Fe3C Proeutectoid Fe3C Eutectoid Fe3C Tertiary Fe3C

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 #
กก    (Properties of Carbon Steel)

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 %C ≤ 0.8% ก $     5 ก
3461 กก    2 #  ! 3!2 !
 
34 "6 ก$   pearlite +    5 ก
34 !#. elongation 6#1 

 %C > 0.8% ก Fe3C (!
!#.$ )  ก/0"#.ก $, network # 
 ก 
 pearlite &1 2 #   ! 3#1  ก 4 elongation ก.   #1 20.ก  !#.2 !
 5 
34# $  
 Fe3C  5 ก
34

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AISI – SAE Steel Specification Series 10xx 11xx 12xx 13xx 23xx 25xx 31xx 33xx ……. 247)

Steel Type Plain carbon steel Plain carbon steel (high S, low P) Plain carbon steel (high S, high P) Mn-Steel (Mn 1.75%) Ni-Steel (Ni 3.00%) Ni-Steel (Ni 5.00%) Ni-Cr Steel (Ni 1.25%, Cr 0.60%) Ni-Cr Steel (Ni 3.50%, Cr 1.50%) (See in Table 7.3 and 7.4, P. 244School of Metallurgical Engineering, SUT

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AISI – SAE Steel Specification

10xx Carbon content/100 Steel type

%Alloying element

2520 20/100 = 0.2 %C Ni-Steel

5.00 %Ni AISI (American Iron and Steel Institute) SAE (Society of Automotive Engineering) JIS ⇨ Japanese Standard DIN ⇨ German Standard School of Metallurgical Engineering, TIS ⇨ Thai Standard SUT

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