Iron carbon phase diagrams Essay

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The Iron–Iron Carbide (Fe–Fe3C) Phase Diagram


In their simplest form, steels are alloys of Iron (Fe) and Carbon (C).



The Fe-C phase diagram is a fairly complex one, but we will only consider the steel part of the diagram, up to around 7% C b d Carbon.



Phases present α-ferrite, γ-ferrite, δ-ferrite, Fe3C (iron carbide or cementite)
Fe-C liquid solution

School of Mechanical and Building Sciences, VIT University, Vellore

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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%
• T
Transforms t FCC γ-austenite at 912 °C f to t it t γ-austenite - solid solution of C in FCC Fe

Fe3C (iron
…show more content…
PM

L(0.53% C) + δ (
(
)
(BCC Ferrite of 0.1% C)
)

B

→ γ (FCC Austenite of 0.18% C)
(
)
N



The maximum solubility of carbon in BCC δ-iron is 0.1% (point M) whereas in FCC γ-iron, it is greater. The presence of carbon influences the allotropic changes. As carbon is increased or added to the iron, the temperature increases from 1400ºC to 1493ºC at
0.1%
0 1% carbon. b School of Mechanical and Building Sciences, VIT University, Vellore

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Peritectic reaction - Fe–Fe3C System
Consider the portion NMPB in Peritectic Reaction


On cooling, the portion NM represents the beginning of the crystal structure change from BCC δ iron to FCC γ iron for alloys

PM

B

containing less than 0 1% carbon
0.1% carbon.


Line MP represents the beginning of crystal structure change by

N

means of peritectic reaction for the alloys between 0.1 & 0.18%
Carbon.


Line NP represents the end of crystal structure change for alloys containing less than 0.18% C.



Portion PB represents the end of crystal structure by means of peritectic reaction for the alloys between 0.18- 0.5% carbon. Here the reaction takes place isothermally (i.e.) at constant temperature.



At the peritectic reaction point, liquid of 0.53% C combines with δ ferrite of 0.1% C to form FCC γ austenite of 0.18% C
School of Mechanical and Building Sciences, VIT University, Vellore

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Eutectic reaction -
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