Iron-carbon phase diagram and the iron-carbon systems are most important binary systems in engineering. Steels, cast irons and various kinds of applications of them are dependent of the iron-carbon systems. We also explained the tin-lead phase diagram and nickel-copper phase diagrams which are also very important in metallurgy and engineerin. In this article we will explain the iron-carbon phase diagram.
The iron carbon phases and phase diagram is slightly complex, compared with other diagrams. The horizontal axis of the Fe-C diagram shows the percentage of carbon inside the Fe-C systems. The solubility limit of carbon inside the iron is very low. So the diagram above shows up to 6.11% of carbon content which is also the solubility limit of carbon inside iron. The two of vertical axes are showing the temperature in which right side Celsius, the left side is Fahreneit.
If we take a look at the pure iron from the left side, there are lots of phases. The first phase that starts from the ambient temperature of pure iron is called alpha solid phase which is also called as ferrite. At 912 Celsius degrees of temperature, the austenite phase of iron is formed. At 1394 celsius degrees, delta phase occurs up to the melting point of pure iron which is 1539 Celsius degrees.
If we take a look at the lattice structures of the phases, the alpha and beta phases of pure iron has BCC lattice structure, and the gamma phase which is between these phases has FCC lattice structure.
As we explained in another article, if the carboın content of the iron-carbon alloy between 0-2.07%, this alloy is called as steel. Steel is one of the most important metals in industry.
At the 0.77% carbon and 723 celsius degrees point, called as eutectoid composition. Steels that has carbon content bigger than 0.77% are called as hyper-eutectoid and other ones are called as hypo-eutectoid steels. There is an another point is called as eutectic point that is occuring at 4.3% of carbon and 1130 celsius degrees temperature.
If the carbon content is between 2.07-6.11%, the alloy is called as cast iron.
There is a F3C phase at the diagram above is prominent at the low temperatures called as cementite. Cementite is the hard and brittle phase of iron-carbon alloy which is solid also.
There general explanation of iron-carbon phase diagram can be like above. Leave your comments and questions about ‘iron-carbon phase diagram’ below!
Image Source: Fundamentals Of Modern Manufacturing