BeginnerTopic 17 of 100Materials & Chemical
Iron-carbon diagram
Describes steels and cast irons including ferrite, austenite and cementite.
In depth
Fe-Fe₃C diagram shows ferrite (α, BCC, max 0.022% C), austenite (γ, FCC, up to 2.14% C), cementite (Fe₃C, 6.67% C), eutectoid at 0.76% C and 727 °C (pearlite) and eutectic at 4.3% C. Steels are below 2.14% C, cast irons above.
Key points
- Pearlite is lamellar ferrite+cementite
- Hypo and hypereutectoid steels
- A1, A3, Acm lines
ExampleA 0.4% C steel cooled slowly is about half ferrite and half pearlite.
What is Iron-carbon diagram?
Describes steels and cast irons including ferrite, austenite and cementite.
Why is it important to understand iron-carbon diagram?
The iron-carbon diagram underlies all steels and cast irons, so it is the reference for nearly every heat treatment and microstructure.
What is the eutectoid composition?
About 0.76 percent carbon, where austenite transforms into pearlite on slow cooling.
What is the difference between steel and cast iron on the diagram?
Steels have less than about 2.1 percent carbon, while cast irons have more and contain a eutectic constituent.
How is Iron-carbon diagram used in practice?
Typical applications include predicting the microstructure of a 0.4 percent carbon steel after slow cooling, choosing a cast iron composition for a machine base and identifying the eutectoid point for a heat treatment design.
What should I learn before Iron-carbon diagram?
Study "Lever rule" first (topic 16 of 100 in Materials & Chemical). It covers the groundwork this topic builds on.
What are the key points of Iron-carbon diagram?
Pearlite is lamellar ferrite+cementite. Hypo and hypereutectoid steels. A1, A3, Acm lines.
Can you give an example of Iron-carbon diagram?
A 0.4% C steel cooled slowly is about half ferrite and half pearlite.
What comes after Iron-carbon diagram?
The next topic is "Steel types", which builds directly on this one.
How difficult is Iron-carbon diagram?
It is classed as Beginner in Materials & Chemical (topic 17 of 100). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.