In the last session, we had learned Different Types of steels, Methods for Manufacturing of Steel & Mechanical Properties of Metals whereas in today's session, we are going to discuss Iron- Carbon Phase Diagram with four Phase Transformations.
Carbon is added to iron as an interstitial inclusion to improve the strength of iron. The maximum solubility of Carbon(C) in Iron(Fe) is 6.67% called critical concentration.
If carbon is added to Iron, it produces Iron Carbide(Fe3C) phase which is hard and brittle also called Cementite.
Note:
In this article, I will be explaining all the important concepts which are either underlined or bolded are useful for all types of examinations. Compulsory, 2 marks will be given from this Iron-Carbon Diagram Theory in any exam.
If the percentage of the carbon is in the range of 0 to 2.11 % then it is called Steel and if the percentage of carbon is in the range of 2.11 to 6.67% then it is called Cast iron.
As the carbon content increases, it produces more Iron-Carbide volume and that phase will exhibit high hardness.
Phase diagrams are graphical representations of the phases present in an alloy at different conditions of chemical composition, temperature, or pressure.
The various phases of the Iron-Carbon Phase Diagram are as follows.
The maximum solubility of carbon is 0.1% at 1493 degrees centigrade.
The four Phase Transformations in Fe-C Diagram are as follows.
The Detailed Explanation of all the above phases is presented below.
The Eutectoid Phase Transformation is as follows.
At ‘S’ point: (Eutectoid Point)
S1--> [S2 + S3]
γFe-->[(αFe) + Fe3C] at 0.8%C @723 Degree Centigrade
Note: (αFe) + Fe3C is called as Pearlite.
In the Iron-Carbon Diagram, the austenite phase(γFe) can undergo a Eutectoid transformation to produce ferrite and cementite called as Pearlite.
The Eutectic Phase Transformation is as follows.
At ‘C’ point:(Eutectic Point)
L (Fe+C)--> [(γFe) + Fe3C] at 4.3%C @1147 Degrees Centigrade
L--> [S2 + S3]
A eutectic reaction is a three-phase reaction, by which on cooling, a liquid transforms into two solid phases at the same time.
The Peritectic Phase Transformation is as follows.
At ‘J’ point:(Peritectic Point)
(δFe+ L)--> (γFe) at 0.17%C @1493 Degree Centigrade
(S1+L )-->S2
The Peritectoid Phase Transformation is as follows.
(S1+S2 )-->S3
Note:
A mixed-phase of (γFe + Fe3C) existing from 4.3% to 6.67% between 723 Degree Centigrade to 1145 Degree Centigrade is known as Ledeburate Phase.
If carbon is added to Iron, it produces Iron Carbide(Fe3C) phase which is hard and brittle also called Cementite.
Phase diagrams are graphical representations of the phases present in an alloy at different conditions of chemical composition,temperature, or pressure.
In the Iron-Carbon Diagram, the austenite phase(γFe) can undergo a Eutectoid transformation to produce ferrite and cementite called as Pearlite.
So this is the detailed explanation of the Iron Carbon Phase Diagram which was explained successfully with the help of important points in bolded and underlined text. If you have any doubts w.r.t. the Iron-Carbon Diagram Theory, you can ask us in the comments section.
More Resources:
Mechanical Properties of Metals
Non-Ferrous Metals
Macroscopic and Microscopic Properties
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